A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observe...A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.展开更多
In this work, we have studied the concentration quenching in transparent glass ceramics containing Er^3＋：NaYF4 nanocrystals. For different concentrations, the emission spectra and decay curves of the ^4I/3/2 → ^4I1...In this work, we have studied the concentration quenching in transparent glass ceramics containing Er^3＋：NaYF4 nanocrystals. For different concentrations, the emission spectra and decay curves of the ^4I/3/2 → ^4I15/2 emission were measured. The Er-concentration dependence of integrated intensity and lifetime of ^4I13/2→^4I15/2 emission are showed. With the increase of the Er^3＋ doping concentration, the 1.5 μm fluorescence emission first increases, then decreases, and the lifetime falls gradually. With 980 nm excitation, the efficiency of the energy transfer from Er^3＋ to quenching centers reaches 73.73% for the sample with 4 mol% Er^3＋. Meanwhile, owing to the relation of fluorescence integrated intensity and Er-concentration, a dipole-dipole quenching mechanism in the framework of a limited diffusion regime has been proved. Using the limited diffusion case, the critical concentration for quenching has been determined from a fitting equation of the lifetime and Er-concentration. The fit- ting result shows the critical concentration for quenching is higher than the values obtained in Er-doped different glass by an order of magnitude.展开更多
The doping concentration of lanthanide ions is important for manipulating the luminescence properties of upconversion nanoparticles （UCNPs）. However, the serious concentration quenching in highly doped UCNPs remains...The doping concentration of lanthanide ions is important for manipulating the luminescence properties of upconversion nanoparticles （UCNPs）. However, the serious concentration quenching in highly doped UCNPs remains a vital restriction for further enhanced upconversion luminescence （UCL）. Herein, we examined the effect of temperature on the concentration quenching of rare-earth UCNPs, an issue that has been overlooked, and we show that it is significant for biomedical or optical applications of UCNPs. In this work, we prepared a series of UCNPs by doping Er3. luminescent centers at different concentrations in a NaLuF4：Yb3＋ matrix. At room temperature （298 K）, steady-state photoluminescence （PL） spectroscopy showed substantial concentration quenching of the Er~ emission with increasing doping concentrations. However, the concentration quenching effect was no longer effective at lower temperatures. Kinetic curves obtained from time-resolved PL spectroscopy further showed that the concen- tration quenching dynamics were vitally altered in the cryogenic temperature region, i.e., below 160 K. Our work on the temperature-switchable concentration quenching mechanism may shed light on improving UCL properties, promoting their practical applications.展开更多
YbF（2.357, YbF3, Ba2 YbF7, and Ba 2 upconversion nanocrystals doped with emitter Er^3＋ ion were synthesized in the same solvent system just with changing the molar ratio of Ba^2＋ to Yb^3＋ in the precursor, which c...YbF（2.357, YbF3, Ba2 YbF7, and Ba 2 upconversion nanocrystals doped with emitter Er^3＋ ion were synthesized in the same solvent system just with changing the molar ratio of Ba^2＋ to Yb^3＋ in the precursor, which corresponed to the crystal phases of rhombohedral, orthorhombic, tetragonal, and cubic, respectively. All the samples emitted both 660 nm red light and 543/523 nm green light which originated from Er^3＋-4f^n electronic transitions ~4F（9/2-~4I（15/2 and ~4S（3/2/~2H（11/2-~4I（15/2, respectively. It was worth mentioning that YbF 3：Er^3＋, Ba2 YbF7：Er^3＋, and BaF2：Er^3＋ could emit dazzlingly bright light even under the excitation of a 980 nm CW laser with output power of 0.1 W. Upconversion emission mechanism analysis indicated that the intensity ratio of red to green light highly depended on the synergistic effect of crystal structure, concentration quenching, and particle size, but were not sensitive to crystallinity as previously reported for NaL nF4（Ln=lanthanide.展开更多
The efficient Eu2＋ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 ℃ for 12h. Photoluminescence （PL） properties sh...The efficient Eu2＋ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 ℃ for 12h. Photoluminescence （PL） properties showed a broad emission band with a peak of 525 nm and the full width of half-emission maximums （FWHM） of 70 nm under 460 nm light irradiation. The X-ray diffraction patterns （XRD） and scanning electron microscope （SEM） images of the synthesized powder demonstrated its pure phase and excellent crystallization. Quenching concentration in this phosphor was found to be 0.3. The mechanisms of concentration quenching and redshift of emission peak with increasing concentration of Eu2＋ were studied. The temperature dependence measurement of this green phosphor revealed excellent thermal quenching property compared to silicate green phosphor. It is believed that Ba3 Si6O12N2 ：Eu2＋ is an excellent green phosphor for UV or blue chip based white LEDs.展开更多
A series of highly Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have been investigated in order to develop a microchip laser at 1.54 μm under 980 nm excitation. Measurements of absorption, emission and upconversi...A series of highly Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have been investigated in order to develop a microchip laser at 1.54 μm under 980 nm excitation. Measurements of absorption, emission and upconversion spectra have been performed to examine the effect of Er^(3+)/Yb^(3+) concentration quenching on spectroscopic properties. In the glasses with Er^(3+) concentrations below 10 mol%, concentration quenching is very low and the Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have stronger fluorescence of 1.54μm due to the ~4I_(13/2)→~4I_(15/2) transition than that of Er^(3+) singly-doped glasses. As Er^(3+) concentrations above 10 mol% in the Er^(3+)/Yb^(3+) co-doped samples, concentration quenching of 1.54μm does obviously occur as a result of the back energy transfer from Er^(3+) to Yb^(3+). To obtain the highest emission efficiency at 1.54μm, the optimum doping-concentration ratio of Er^(3+)/Yb^(3+) was found to be approximately 1:1 in mol fraction when the Er^(3+) concentration is less than 10 mol%.展开更多
Luminescence quench is common in overdoped upconversion nanoparticles.Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence,but in upconversion nanoparticles t...Luminescence quench is common in overdoped upconversion nanoparticles.Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence,but in upconversion nanoparticles that are highly doped with both sensitizers and activators,the factors that contribute to the diminishing of the emission cannot be summarized by a single cause.Herein,a core-shell design is used to spatially separate the sensitizer(Yb^(3+))and activator(Er^(3+))and to modulate the emission by changes in the distribution position as well as the concentration of the dopant ions in order to probe the factors affecting the luminescence.When the sensitizer ions are located in the core,the luminescence intensity of the nanoparticles is significantly weaker than that of the other distribution,which implies that the effect of sensitizer and activator on luminescence in the highly doped state has a different and more complex mechanism.The intensity of the emission is more affected by Yb^(3+)than Er^(3+),which includes not only the self-quenching of Yb^(3+),but also the dominance in the Yb^(3+)-Er^(3+)cross-relaxation.In this finding may provide new ideas for revealing the reasons for the diminished luminescence of highly doped upconversion nanoparticles and thus for enhancing luminescence.展开更多
The new phosphors Bi2ZnB2O7:Ln3+ (Ln3+=Eu3+,Dy3+) were synthesized by solid-state reaction technique.The obtained phosphors were investigated by means of X-ray powder diffraction (XRD),photoluminescence excitation and...The new phosphors Bi2ZnB2O7:Ln3+ (Ln3+=Eu3+,Dy3+) were synthesized by solid-state reaction technique.The obtained phosphors were investigated by means of X-ray powder diffraction (XRD),photoluminescence excitation and emission spectra with the aim of enhancing the fundamental knowledge about the luminescent properties of Eu3+ and Dy3+ ions in the Bi2ZnB2O7 host lattice.XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7.The excitation and emission spectra of Bi2ZnB2O7:Ln3+ (Ln3+=Eu3+,Dy3+) at room temperature show the typical 4f-4f transitions of Eu3+ and Dy3+,respectively.The hypersensitive transitions of 5D0→7F2 (Eu3+) and 4F9/2→6H13/2 (Dy3+) are relatively higher than those of the insensitive transitions in Bi2ZnB2O7.It is conceivable that the Bi2ZnB2O7 structure provides asymmetry sites for activators (Eu3+,Dy3+).The optimum concentrations of Eu3+ and Dy3+ ions in Bi2ZnB2O7 phosphors are both x=0.05.展开更多
Y, Gd)Al 3(BO 3) 4∶Eu 3+ samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered ...Y, Gd)Al 3(BO 3) 4∶Eu 3+ samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd 3+ mole concentration in the range of 0.15 to 0.85 mol (and Eu 3+ mole concentration, 0.02 to 0.1 mol). The correlative data show that the concentration quenching occurs when the Eu 3+ mole concentration ranges from 0.02 to 0.1 mol, and the Gd 3+→Gd 3+, Gd 3+→Eu 3+ and host→Eu 3+, Gd 3+ energy transfers exist, and Gd 3+ mole concentration influences Eu 3+ emission.展开更多
The phosphors of （Bi1- x Smx ） 2ZnB2O7 （ x = 0. 01, 0. 03, 0. 05, 0. 07, and 0. 09） were synthesized by conventional solid state reaction. The purity of all samples was checked by X-ray powder diffraction （XRD）....The phosphors of （Bi1- x Smx ） 2ZnB2O7 （ x = 0. 01, 0. 03, 0. 05, 0. 07, and 0. 09） were synthesized by conventional solid state reaction. The purity of all samples was checked by X-ray powder diffraction （XRD）. XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7, indicating that the Bi^3＋ in Bi2ZnB2O7 can be partly replaced by the Sm^3＋ without the change of crystal structure. The excitation and emission spectra at room temperature show the typical 4f-4f transitions of Sm^3＋ . The dominant excitation line is around 404 nm due to ^6H5/2→^4K11/2 and the emission spectrum consists of a series of lines at 563, 599, 646, and 704 nm due to ^4G5/2→^6H5/2, ^6H7/2, ^6H9/2, and ^6H11/2, respectively. The optimal concentration of Sm^3＋ in Bi2ZnB2O7 is about 3mol% （relative to lmol Bi^3＋ ） and the critical distance Rc was calculated as 2.1 nm. The temperature dependence of the emission intensity of Bi1.94Sm0.06ZnB2O7 was examined in the temperature range between 100 and 450 K. The quenching temperature where the intensity has dropped to half of the initial intensity is 280 K. The lifetime for Sm^3＋ in Bi1.94Sm0.06ZnB2O7 is fitted as a value of 0.29 and 1.03 ms.展开更多
This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3＋-doped solid-state crystals mainly on cubic crystals with 99.99% pur...This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3＋-doped solid-state crystals mainly on cubic crystals with 99.99% purity which could be extended to laser ceramics of the same composition.展开更多
Nanocrystalline monoclinic and cubic Gd 2O 3∶Eu with different Eu 3+ concentration were prepared using glycine-nitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, p...Nanocrystalline monoclinic and cubic Gd 2O 3∶Eu with different Eu 3+ concentration were prepared using glycine-nitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, pure monoclinic and cubic Gd 2O 3∶Eu with particle size less than 40 nm can be easily formed. Under ultraviolet excitation, main emission of Eu 3+ ( 5D 0→ 7F 2) locates at 624 nm in monoclinic Gd 2O 3∶Eu and 611 nm in cubic sample. In excitation spectrum two broad bands corresponding to the host absorption and charge transfer state (CTS) and f-f transitions of Gd 3+ and Eu 3+ were observed and discussed. The quenching concentration of monoclinic and cubic Gd 2O 3∶Eu is 10% and 15%, respectively, both of which are much higher than that of bulk Gd 2O 3∶Eu.展开更多
Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate ...Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate as precipitant. The phase evolution and morphology of the precursor were characterized with X-ray diffractometer （XRD） and transmission electron microscopy （TEM）. The resultant LuAG：Pr^3＋ powder was sintered into translucent ceramic without any additives in vacuum at 1150 ℃ and then in nitrogen atmosphere at 1700 ℃. spectra of LuAG：Pr^3＋ powder and ceramic were measured at room temperature in vacuum ultraviolet （VUV） and ultraviolet （VU） region. For the 5d-4f transition of Pr^3＋ ions, dominant emission of ceramic samples peaking round 311 um had higher luminescence intensity. And the host absorption in ceramic samples was not as intensive as that in powder samples. The luminescent intensity of LuAG：Pr^3＋ varied with the Pr^3＋ contents and the quenching concentration was about 1.0at.% for ceramic and 3.0at.% for powder, which was much higher than 0.24at.% for LuAG：Pr^3＋ single crystals. This phenomenon showed that the ceramic had some superiority over single crystals.展开更多
The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emissi...The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emission intensity and the yellow to blue intensity ratio (Y/B) of Dy^(3+) were investigated too. The results obtained indicate that Ce^(3+) can sensitize the luminescence of Dy^(3+). The optimum concentration of Dy^(3+) in Ba_3La(BO_3)_3 is x_(Dy)=0.06. According to the dependence of the concentration of Dy^(3+) in Ba_3La(BO_3)_3 under the excitation of 350 nm, it is confirmed that the mechanism of concentration selfquenching of Dy^(3+) () (()~4F_(9/2)→()~6H_(15/2),) (()~6H_(13/2)) transition is electric dipole-quadrupole interaction.展开更多
The structure and photoluminescence （PL） properties of Sr3 SiO5： Sm3＋ and Li＋-doped Sr3SiOs： Sm3＋ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL s...The structure and photoluminescence （PL） properties of Sr3 SiO5： Sm3＋ and Li＋-doped Sr3SiOs： Sm3＋ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm3＋ concentration is beyond 1.3 mol% in Sr3SiOs： Sm3＋ phosphor without doping Li＋ ions. The concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of Sm3＋ ions. The incorporation of Li＋ ions into Sr3SiOs： Sm3＋ phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm3＋ with concentration increased from 1.3 tool% to 1.7 tool%.展开更多
Tb3+ doped boro-alumina-silicate glasses were synthesized in air by high temperature process. Optical absorption, emission and excitation spectra of the glasses have been measured. Effect of concentration quenching on...Tb3+ doped boro-alumina-silicate glasses were synthesized in air by high temperature process. Optical absorption, emission and excitation spectra of the glasses have been measured. Effect of concentration quenching on the lifetime and fluorescence yield of 5D3 and 5D4 level has been discussed. The absorption spectrum shows four poor peaks in the UV-Vis region. With excitation at 377 nm, the fluorescence spectrum of the sample has four major emission bands at 488, 542, 584 and 621 nm, which correspond to the 5D4→7Fj (j=6, 5, 4, 3) transitions respectively. The emission from the 5D3→7Fj (j=5, 4, 3) transitions around 415, 437 and 458 nm are very feeble. When Tb3+ concentration beyond a particular value (2%, mole fraction), the concentration quenching phenomenon of 5D3 state occurred, due to the dipole-dipole interaction among the Tb3+. The energy transfer process (5D3+7F6→5D4+7F0) leads to a high quenching concentration (up to 20%) of 5D4 state. The lifetime of 5D4 level in boro-alumina-silicate glass is about 3ms that can be used for new type of long-lasting phosphorescence device.展开更多
Dy3+-doped boroaluminasilicate(BAS) glasses with high effective visible fluorescence emission were synthesized. Optical absorption and fluorescence spectra of these glasses have been studied. Using J-O theory, the int...Dy3+-doped boroaluminasilicate(BAS) glasses with high effective visible fluorescence emission were synthesized. Optical absorption and fluorescence spectra of these glasses have been studied. Using J-O theory, the intensity parameters (×10-20 cm2) Ω2=4.75, Ω4=0.98 and Ω6=2.24 have been evaluated with a reasonable agreement between the measured and calculated f-value. These parameters were used to predict various spectroscopic properties of excited levels of Dy3+ in BAS glasses. The bright yellow emission at 575 nm (4F9/2→6H13/2) has been observed, apart from 4F9/2→6H15/2 (482 nm) and 4F9/2→6H11/2 (662 nm) emission transitions with excitation at 451 nm (6H15/2→4H15/2). Stimulated emission cross-sections of the emission bands have been computed based on the measured Δλ. Concentration quenching will occur when concentration of Dy3+ exceeds 1.0%(mole fraction) and the quenching mechanism involves quadrupole-quadrupole interaction.展开更多
High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion(UC)nanocrystals(UCNC)like NaYF_(4):Yb,Er and first strategies were reported ...High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion(UC)nanocrystals(UCNC)like NaYF_(4):Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC.UC luminescence(UCL)is,however,controlled not only by dopant concentration,yet by an interplay of different parameters including size,crystal and shell quality,and excitation power density(P).Thus,identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy.Here,we quantify the dopant concentration dependence of the UCL quantum yield(ΦUC)of solid NaYF_(4):Yb,Er/NaYF_(4):Lu upconversion core/shell nanocrystals of varying Yb3+and Er3+concentrations(Yb3+series:20%‒98%Yb3+;2%Er3+;Er3+series:60%Yb3+;2%‒40%Er3+).To circumvent other luminescence quenching processes,an elaborate synthesis yielding OH-free UCNC with recordΦUC of~9%and~25 nm core particles with a thick surface shell were used.High Yb3+concentrations barely reduceΦUC from~9%(20%Yb3+)to~7%(98%Yb3+)for an Er3+concentration of 2%,thereby allowing to strongly increase the particle absorption cross section and UCNC brightness.Although an increased Er3+concentration reducesΦUC from~7%(2%Er3+)to 1%(40%)for 60%Yb3+.Nevertheless,at very high P(>1 MW/cm^(2))used for microscopic studies,highly Er3+-doped UCNC display a high brightness because of reduced saturation.These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.展开更多
Spherical(Y_(0.98)Er_(0.02))_(2)(OH)_(5)(NO_(3))·xH_(2)O particles were synthesized by controlled double-jet precipitation,with a“core”of pure layered yttrium hydroxide nitrate,and a“shell”of co-precipitated ...Spherical(Y_(0.98)Er_(0.02))_(2)(OH)_(5)(NO_(3))·xH_(2)O particles were synthesized by controlled double-jet precipitation,with a“core”of pure layered yttrium hydroxide nitrate,and a“shell”of co-precipitated yttrium-erbium layered hydroxide nitrates.With an increase in precipitation pH from 7 to 9.5,the size of layered“building units”decreases and the architecture of their assemblies changes from flower-like through network-like spherical to irregular agglomerates.From there,spherical particles gradually increase their diameter due to the continuous uniform growth of curved layered sheets on their surface.It was established that such growth behavior and network-like architecture of spherical particles was retained even when yttrium was replaced by erbium ions in the layered host lattice during the formation of an Er-enriched“shell”.Analysis of SEM,EDS,XPS,photoluminescence spectra and concentration quenching effects of heat-treated Y_(2)O_(3):Er(2 at.%)particles indicate that the radial distribution of erbium in particles is most controllable in a narrow pH range of co-precipitation of layered precursors(pH8).Вy widely varying the elemental composition of“building units”during co-precipitation,one can simultaneously finely control the composition of layered hydroxides in the radial direction of the spherical particles and grow multicomponent“multi-shell”powders with desired properties.展开更多
Yellow-emitting YAG：Ce3＋ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions （...Yellow-emitting YAG：Ce3＋ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions （MRCM）, pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 ℃. The phosphors exhibited the charactefistc broadband visible luminescence of YAG：Ce. The optimum concentration of Ce3＋ was 1.0 tool.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole （d-q）. Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem- perature. The Y3Al5O12：Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG：Ce.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10974013, 60978060, and 10804006)the Research Fund for the Doctoral Program of Higher Education, China (Grant No. 20090009110027)+5 种基金the Beijing Municipal Natural Science Foundation, China (Grant No. 1102028)the National Basic Research Program of China (Grant No. 2010CB327704)the National Natural Science Foundation for Distinguished Young Scholars (Grant No. 60825407)the Beijing Municipal Science and Technology Commission, China (Grant No. Z090803044009001)the Science Fund of the Key Laboratory of Luminescence and Optical Information, Beijing Jiaotong University, Ministry of Education, China (Grant No. 2010LOI12)the Excellent Doctor's Science and Technology Innovation Foundation of Beijing Jiaotong University, China (Grant No. 2011YJS073)
文摘A yellow phosphor, Ca2BO3CI：Eu2＋, is prepared by the high-temperature solid-state method. Under the condition of excitation sources ranging from ultraviolet to visible light, efficient yellow emission can be observed. The emission spectrum shows an asymmetrical single intensive band centred at 573 nm, which corresponds to the 4f65dl→4f7 transition of Eu2＋. Eu2＋ ions occupy two types of Ca2＋ sites in the Ca2BO3C1 lattice and form two corresponding emission centres, respectively, which lead to the asymmetrical emission of Eu2＋ in Ca2BO3C1. The emission intensity of Eu2＋ in Ca2BO3C1 is influenced by the Eu2＋ doping concentration. Concentration quenching is discovered, and its mechanism is verified to be a dipole-dipole interaction. The value of the critical transfer distance is calculated to be 2.166 nm, which is in good agreement with the 2.120 nm value derived from the experimental data.
基金supported by the Fujian Natural Science Foundation of China (Grant No. 2009J05139)the Fujian Science and Technology major projects of China (Grant No. 2007HJ0004-2)+1 种基金the Project of Education Department of Fujian Province of China (Grant No. JK2011008)the Innovation Project for Young Scientists of Fujian Province of China (Grant No. 2007F3027)
文摘In this work, we have studied the concentration quenching in transparent glass ceramics containing Er^3＋：NaYF4 nanocrystals. For different concentrations, the emission spectra and decay curves of the ^4I/3/2 → ^4I15/2 emission were measured. The Er-concentration dependence of integrated intensity and lifetime of ^4I13/2→^4I15/2 emission are showed. With the increase of the Er^3＋ doping concentration, the 1.5 μm fluorescence emission first increases, then decreases, and the lifetime falls gradually. With 980 nm excitation, the efficiency of the energy transfer from Er^3＋ to quenching centers reaches 73.73% for the sample with 4 mol% Er^3＋. Meanwhile, owing to the relation of fluorescence integrated intensity and Er-concentration, a dipole-dipole quenching mechanism in the framework of a limited diffusion regime has been proved. Using the limited diffusion case, the critical concentration for quenching has been determined from a fitting equation of the lifetime and Er-concentration. The fit- ting result shows the critical concentration for quenching is higher than the values obtained in Er-doped different glass by an order of magnitude.
基金This work was supported by the National Natural Science Foundation of China （Nos. 21373268, 21301121, and 21227803）, the open funding of Renmin University of China （Nos. 15XNLQ04 and 10XNI007）, and the open funding of the State Key Laboratory on Integrated Optoelectronics of Jilin University （No. IOSKL2015KF33）.
文摘The doping concentration of lanthanide ions is important for manipulating the luminescence properties of upconversion nanoparticles （UCNPs）. However, the serious concentration quenching in highly doped UCNPs remains a vital restriction for further enhanced upconversion luminescence （UCL）. Herein, we examined the effect of temperature on the concentration quenching of rare-earth UCNPs, an issue that has been overlooked, and we show that it is significant for biomedical or optical applications of UCNPs. In this work, we prepared a series of UCNPs by doping Er3. luminescent centers at different concentrations in a NaLuF4：Yb3＋ matrix. At room temperature （298 K）, steady-state photoluminescence （PL） spectroscopy showed substantial concentration quenching of the Er~ emission with increasing doping concentrations. However, the concentration quenching effect was no longer effective at lower temperatures. Kinetic curves obtained from time-resolved PL spectroscopy further showed that the concen- tration quenching dynamics were vitally altered in the cryogenic temperature region, i.e., below 160 K. Our work on the temperature-switchable concentration quenching mechanism may shed light on improving UCL properties, promoting their practical applications.
基金Project supported by the National Natural Science Foundation of China(11274263,21301058,11274263)
文摘YbF（2.357, YbF3, Ba2 YbF7, and Ba 2 upconversion nanocrystals doped with emitter Er^3＋ ion were synthesized in the same solvent system just with changing the molar ratio of Ba^2＋ to Yb^3＋ in the precursor, which corresponed to the crystal phases of rhombohedral, orthorhombic, tetragonal, and cubic, respectively. All the samples emitted both 660 nm red light and 543/523 nm green light which originated from Er^3＋-4f^n electronic transitions ~4F（9/2-~4I（15/2 and ~4S（3/2/~2H（11/2-~4I（15/2, respectively. It was worth mentioning that YbF 3：Er^3＋, Ba2 YbF7：Er^3＋, and BaF2：Er^3＋ could emit dazzlingly bright light even under the excitation of a 980 nm CW laser with output power of 0.1 W. Upconversion emission mechanism analysis indicated that the intensity ratio of red to green light highly depended on the synergistic effect of crystal structure, concentration quenching, and particle size, but were not sensitive to crystallinity as previously reported for NaL nF4（Ln=lanthanide.
基金Project supported by National Natural Science Foundation of China(51102021)the Natural Science Foundation of Beijing(2102022)the National High Technology Research and Development Program of China(2010AA03A404,2011AA03A101)
文摘The efficient Eu2＋ -doped Ba3 Si6O12N2 green phosphors were prepared by a traditional solid state reaction method under N2 /H2 atmosphere at a temperature up to 1350 ℃ for 12h. Photoluminescence （PL） properties showed a broad emission band with a peak of 525 nm and the full width of half-emission maximums （FWHM） of 70 nm under 460 nm light irradiation. The X-ray diffraction patterns （XRD） and scanning electron microscope （SEM） images of the synthesized powder demonstrated its pure phase and excellent crystallization. Quenching concentration in this phosphor was found to be 0.3. The mechanisms of concentration quenching and redshift of emission peak with increasing concentration of Eu2＋ were studied. The temperature dependence measurement of this green phosphor revealed excellent thermal quenching property compared to silicate green phosphor. It is believed that Ba3 Si6O12N2 ：Eu2＋ is an excellent green phosphor for UV or blue chip based white LEDs.
基金This work was supported by the Rising-Star Project(No. 04QMX1448) of Shanghai Municipal Science and Technology Commission the National Natural Science Foundation of China (No. 60207006).
文摘A series of highly Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have been investigated in order to develop a microchip laser at 1.54 μm under 980 nm excitation. Measurements of absorption, emission and upconversion spectra have been performed to examine the effect of Er^(3+)/Yb^(3+) concentration quenching on spectroscopic properties. In the glasses with Er^(3+) concentrations below 10 mol%, concentration quenching is very low and the Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have stronger fluorescence of 1.54μm due to the ~4I_(13/2)→~4I_(15/2) transition than that of Er^(3+) singly-doped glasses. As Er^(3+) concentrations above 10 mol% in the Er^(3+)/Yb^(3+) co-doped samples, concentration quenching of 1.54μm does obviously occur as a result of the back energy transfer from Er^(3+) to Yb^(3+). To obtain the highest emission efficiency at 1.54μm, the optimum doping-concentration ratio of Er^(3+)/Yb^(3+) was found to be approximately 1:1 in mol fraction when the Er^(3+) concentration is less than 10 mol%.
基金support from the National Natural Science Foundation of China(No.22275120)the Science and Technology Commission of Shanghai Municipality(No.22520711600).
文摘Luminescence quench is common in overdoped upconversion nanoparticles.Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence,but in upconversion nanoparticles that are highly doped with both sensitizers and activators,the factors that contribute to the diminishing of the emission cannot be summarized by a single cause.Herein,a core-shell design is used to spatially separate the sensitizer(Yb^(3+))and activator(Er^(3+))and to modulate the emission by changes in the distribution position as well as the concentration of the dopant ions in order to probe the factors affecting the luminescence.When the sensitizer ions are located in the core,the luminescence intensity of the nanoparticles is significantly weaker than that of the other distribution,which implies that the effect of sensitizer and activator on luminescence in the highly doped state has a different and more complex mechanism.The intensity of the emission is more affected by Yb^(3+)than Er^(3+),which includes not only the self-quenching of Yb^(3+),but also the dominance in the Yb^(3+)-Er^(3+)cross-relaxation.In this finding may provide new ideas for revealing the reasons for the diminished luminescence of highly doped upconversion nanoparticles and thus for enhancing luminescence.
基金supported by the National Natural Science Foundation of China (No.20501023)the Youth Research Fund Project of Guangzhou Research Institute of Non-ferrous Metals
文摘The new phosphors Bi2ZnB2O7:Ln3+ (Ln3+=Eu3+,Dy3+) were synthesized by solid-state reaction technique.The obtained phosphors were investigated by means of X-ray powder diffraction (XRD),photoluminescence excitation and emission spectra with the aim of enhancing the fundamental knowledge about the luminescent properties of Eu3+ and Dy3+ ions in the Bi2ZnB2O7 host lattice.XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7.The excitation and emission spectra of Bi2ZnB2O7:Ln3+ (Ln3+=Eu3+,Dy3+) at room temperature show the typical 4f-4f transitions of Eu3+ and Dy3+,respectively.The hypersensitive transitions of 5D0→7F2 (Eu3+) and 4F9/2→6H13/2 (Dy3+) are relatively higher than those of the insensitive transitions in Bi2ZnB2O7.It is conceivable that the Bi2ZnB2O7 structure provides asymmetry sites for activators (Eu3+,Dy3+).The optimum concentrations of Eu3+ and Dy3+ ions in Bi2ZnB2O7 phosphors are both x=0.05.
文摘Y, Gd)Al 3(BO 3) 4∶Eu 3+ samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd 3+ mole concentration in the range of 0.15 to 0.85 mol (and Eu 3+ mole concentration, 0.02 to 0.1 mol). The correlative data show that the concentration quenching occurs when the Eu 3+ mole concentration ranges from 0.02 to 0.1 mol, and the Gd 3+→Gd 3+, Gd 3+→Eu 3+ and host→Eu 3+, Gd 3+ energy transfers exist, and Gd 3+ mole concentration influences Eu 3+ emission.
基金Project supported by the National Natural Science Foundation of China (20501023) and the Guangdong Provincial NaturalScience Foundation (5300527)
文摘The phosphors of （Bi1- x Smx ） 2ZnB2O7 （ x = 0. 01, 0. 03, 0. 05, 0. 07, and 0. 09） were synthesized by conventional solid state reaction. The purity of all samples was checked by X-ray powder diffraction （XRD）. XRD analysis shows that all these compounds are of a single phase of Bi2ZnB2O7, indicating that the Bi^3＋ in Bi2ZnB2O7 can be partly replaced by the Sm^3＋ without the change of crystal structure. The excitation and emission spectra at room temperature show the typical 4f-4f transitions of Sm^3＋ . The dominant excitation line is around 404 nm due to ^6H5/2→^4K11/2 and the emission spectrum consists of a series of lines at 563, 599, 646, and 704 nm due to ^4G5/2→^6H5/2, ^6H7/2, ^6H9/2, and ^6H11/2, respectively. The optimal concentration of Sm^3＋ in Bi2ZnB2O7 is about 3mol% （relative to lmol Bi^3＋ ） and the critical distance Rc was calculated as 2.1 nm. The temperature dependence of the emission intensity of Bi1.94Sm0.06ZnB2O7 was examined in the temperature range between 100 and 450 K. The quenching temperature where the intensity has dropped to half of the initial intensity is 280 K. The lifetime for Sm^3＋ in Bi1.94Sm0.06ZnB2O7 is fitted as a value of 0.29 and 1.03 ms.
文摘This was an outlook on the prediction of the infrared laser potentiality from concentration dependences of the 2F5/2 experimental decay time in Yb3＋-doped solid-state crystals mainly on cubic crystals with 99.99% purity which could be extended to laser ceramics of the same composition.
文摘Nanocrystalline monoclinic and cubic Gd 2O 3∶Eu with different Eu 3+ concentration were prepared using glycine-nitrate combustion synthesis. By changing the ratio of glycine to nitrate and proper heat treatment, pure monoclinic and cubic Gd 2O 3∶Eu with particle size less than 40 nm can be easily formed. Under ultraviolet excitation, main emission of Eu 3+ ( 5D 0→ 7F 2) locates at 624 nm in monoclinic Gd 2O 3∶Eu and 611 nm in cubic sample. In excitation spectrum two broad bands corresponding to the host absorption and charge transfer state (CTS) and f-f transitions of Gd 3+ and Eu 3+ were observed and discussed. The quenching concentration of monoclinic and cubic Gd 2O 3∶Eu is 10% and 15%, respectively, both of which are much higher than that of bulk Gd 2O 3∶Eu.
基金supported by the National Natural Science Foundation of China (10774140)Funds for International Cooperation and Exchange of the National Nature Science Foundation of China (50711120504)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education (20060358054)Special Foundation for Talents of Anhui Province, China (2007Z021)
文摘Lutetium aluminum garnet （LuAG） precursors doped with different Pr^3＋ concentration （0.25at.%, 0.5at.%, 1.0at.%, 3.0at.%, 5.0at.%） were synthesized via a co-precipitation method using ammonium hydrogen carbonate as precipitant. The phase evolution and morphology of the precursor were characterized with X-ray diffractometer （XRD） and transmission electron microscopy （TEM）. The resultant LuAG：Pr^3＋ powder was sintered into translucent ceramic without any additives in vacuum at 1150 ℃ and then in nitrogen atmosphere at 1700 ℃. spectra of LuAG：Pr^3＋ powder and ceramic were measured at room temperature in vacuum ultraviolet （VUV） and ultraviolet （VU） region. For the 5d-4f transition of Pr^3＋ ions, dominant emission of ceramic samples peaking round 311 um had higher luminescence intensity. And the host absorption in ceramic samples was not as intensive as that in powder samples. The luminescent intensity of LuAG：Pr^3＋ varied with the Pr^3＋ contents and the quenching concentration was about 1.0at.% for ceramic and 3.0at.% for powder, which was much higher than 0.24at.% for LuAG：Pr^3＋ single crystals. This phenomenon showed that the ceramic had some superiority over single crystals.
文摘The photoluminescence of Dy^(3+) doped and Dy^(3+), Ce^(3+) codoped in Ba_3La(BO_3)_3 were studied. The dependence of the charge-to-radius ratio (z/r) for RE^(3+)(RE=La, Ce), the Ce^(3+), Dy^(3+) content on the emission intensity and the yellow to blue intensity ratio (Y/B) of Dy^(3+) were investigated too. The results obtained indicate that Ce^(3+) can sensitize the luminescence of Dy^(3+). The optimum concentration of Dy^(3+) in Ba_3La(BO_3)_3 is x_(Dy)=0.06. According to the dependence of the concentration of Dy^(3+) in Ba_3La(BO_3)_3 under the excitation of 350 nm, it is confirmed that the mechanism of concentration selfquenching of Dy^(3+) () (()~4F_(9/2)→()~6H_(15/2),) (()~6H_(13/2)) transition is electric dipole-quadrupole interaction.
基金supported by the National Natural Science Foundation of China (Grant No. 11204113)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20115314120001)+1 种基金the China Postdoctoral Science Foundation (Grant No. 2011M501424)the Natural Science Foundation of Yunnan Province, China (Grant No. 2011FB022)
文摘The structure and photoluminescence （PL） properties of Sr3 SiO5： Sm3＋ and Li＋-doped Sr3SiOs： Sm3＋ red-emitting phosphors were investigated. Samples were prepared by the high-temperature solid-state method. PL spectra show that the concentration quenching occurs when the Sm3＋ concentration is beyond 1.3 mol% in Sr3SiOs： Sm3＋ phosphor without doping Li＋ ions. The concentration-quenching mechanism can be explained by the electric dipole-dipole interaction of Sm3＋ ions. The incorporation of Li＋ ions into Sr3SiOs： Sm3＋ phosphors, as a charge compensator, improves the PL properties. The lithium ions also suppress the concentration quenching in Sm3＋ with concentration increased from 1.3 tool% to 1.7 tool%.
基金Trans-Century Training Programme Foundation for the Talents by the Ministry of EducationNatural Science Fund of Jiangsu Province (BK2004121)the Innovation Foundation for Graduate Students of Jiangsu Province
文摘Tb3+ doped boro-alumina-silicate glasses were synthesized in air by high temperature process. Optical absorption, emission and excitation spectra of the glasses have been measured. Effect of concentration quenching on the lifetime and fluorescence yield of 5D3 and 5D4 level has been discussed. The absorption spectrum shows four poor peaks in the UV-Vis region. With excitation at 377 nm, the fluorescence spectrum of the sample has four major emission bands at 488, 542, 584 and 621 nm, which correspond to the 5D4→7Fj (j=6, 5, 4, 3) transitions respectively. The emission from the 5D3→7Fj (j=5, 4, 3) transitions around 415, 437 and 458 nm are very feeble. When Tb3+ concentration beyond a particular value (2%, mole fraction), the concentration quenching phenomenon of 5D3 state occurred, due to the dipole-dipole interaction among the Tb3+. The energy transfer process (5D3+7F6→5D4+7F0) leads to a high quenching concentration (up to 20%) of 5D4 state. The lifetime of 5D4 level in boro-alumina-silicate glass is about 3ms that can be used for new type of long-lasting phosphorescence device.
基金Trans-Century Training Programme Foundation for the Talents by the Ministry of EducationNatural Science Fund of Jiangsu Province (BK2004121)
文摘Dy3+-doped boroaluminasilicate(BAS) glasses with high effective visible fluorescence emission were synthesized. Optical absorption and fluorescence spectra of these glasses have been studied. Using J-O theory, the intensity parameters (×10-20 cm2) Ω2=4.75, Ω4=0.98 and Ω6=2.24 have been evaluated with a reasonable agreement between the measured and calculated f-value. These parameters were used to predict various spectroscopic properties of excited levels of Dy3+ in BAS glasses. The bright yellow emission at 575 nm (4F9/2→6H13/2) has been observed, apart from 4F9/2→6H15/2 (482 nm) and 4F9/2→6H11/2 (662 nm) emission transitions with excitation at 451 nm (6H15/2→4H15/2). Stimulated emission cross-sections of the emission bands have been computed based on the measured Δλ. Concentration quenching will occur when concentration of Dy3+ exceeds 1.0%(mole fraction) and the quenching mechanism involves quadrupole-quadrupole interaction.
基金the German Science Foundation DFG(grants RE 1203/18-1 and HA 1649/7-1)the EU(COST 1403)for financial support.
文摘High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion(UC)nanocrystals(UCNC)like NaYF_(4):Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC.UC luminescence(UCL)is,however,controlled not only by dopant concentration,yet by an interplay of different parameters including size,crystal and shell quality,and excitation power density(P).Thus,identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy.Here,we quantify the dopant concentration dependence of the UCL quantum yield(ΦUC)of solid NaYF_(4):Yb,Er/NaYF_(4):Lu upconversion core/shell nanocrystals of varying Yb3+and Er3+concentrations(Yb3+series:20%‒98%Yb3+;2%Er3+;Er3+series:60%Yb3+;2%‒40%Er3+).To circumvent other luminescence quenching processes,an elaborate synthesis yielding OH-free UCNC with recordΦUC of~9%and~25 nm core particles with a thick surface shell were used.High Yb3+concentrations barely reduceΦUC from~9%(20%Yb3+)to~7%(98%Yb3+)for an Er3+concentration of 2%,thereby allowing to strongly increase the particle absorption cross section and UCNC brightness.Although an increased Er3+concentration reducesΦUC from~7%(2%Er3+)to 1%(40%)for 60%Yb3+.Nevertheless,at very high P(>1 MW/cm^(2))used for microscopic studies,highly Er3+-doped UCNC display a high brightness because of reduced saturation.These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.
基金Minobrnauki (project FEUZ-2020-0059)the Russian Science Foundation (agreement No.21-12-00392)for financial support.
文摘Spherical(Y_(0.98)Er_(0.02))_(2)(OH)_(5)(NO_(3))·xH_(2)O particles were synthesized by controlled double-jet precipitation,with a“core”of pure layered yttrium hydroxide nitrate,and a“shell”of co-precipitated yttrium-erbium layered hydroxide nitrates.With an increase in precipitation pH from 7 to 9.5,the size of layered“building units”decreases and the architecture of their assemblies changes from flower-like through network-like spherical to irregular agglomerates.From there,spherical particles gradually increase their diameter due to the continuous uniform growth of curved layered sheets on their surface.It was established that such growth behavior and network-like architecture of spherical particles was retained even when yttrium was replaced by erbium ions in the layered host lattice during the formation of an Er-enriched“shell”.Analysis of SEM,EDS,XPS,photoluminescence spectra and concentration quenching effects of heat-treated Y_(2)O_(3):Er(2 at.%)particles indicate that the radial distribution of erbium in particles is most controllable in a narrow pH range of co-precipitation of layered precursors(pH8).Вy widely varying the elemental composition of“building units”during co-precipitation,one can simultaneously finely control the composition of layered hydroxides in the radial direction of the spherical particles and grow multicomponent“multi-shell”powders with desired properties.
基金Project supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)Jiangsu Provincial Natural Sciences Fund (BK2007724)
文摘Yellow-emitting YAG：Ce3＋ nanocrystalline phosphors were prepared by citrate sol-gel combustion method using citric acid as the fuel and chelating agent. The influence of mole ratio of citric acid to metallic ions （MRCM）, pH value of the solution, calcination temperature and Ce-doped concentration on the structures and properties of as-prepared powders were investigated in detail. Higher crystallinity and better luminescence performance powders were obtained at MRCM=2, pH=3 and the calcination temperature of 1200 ℃. The phosphors exhibited the charactefistc broadband visible luminescence of YAG：Ce. The optimum concentration of Ce3＋ was 1.0 tool.%, and the concentration quenching was derived from the reciprocity between electric dipole and electric quadrupole （d-q）. Especially, the pH value of the solution was a key factor to obtain a stable sol-gel system and then obtain pure and homogeneous rare earth ions doped YAG phosphors at a lower tem- perature. The Y3Al5O12：Ce0.03 phosphor with optimized synthesis-condition and composition had a similar luminescence intensity with the commercial phosphor YAG：Ce.
