Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,th...Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,the huge efficiency losses caused by integrating the PD and QLED together hasn’t been studied sufficiently.This work revealed at least three origins for the efficiency losses.First,the PD unit and QLED unit usually didn’t work under optimal conditions at the same time.Second,the potential barriers and traps at the interconnection between PD and QLED units induced unfavorable carrier recombination.Third,much emitted visible light was lost due to the strong visible absorption in the PD unit.Based on the understandings on the loss mechanisms,the infrared up-conversion photodetectors were optimized and achieved a breakthrough photon-to-photon conversion efficiency of 6.9%.This study provided valuable guidance on how to optimize the way of integration for up-conversion photodetectors.展开更多
Cowpea (Vigna unguiculata L. Walp) is a multi-purpose legume with high quality protein for human consumption and livestock. The objective of this work was to develop near-infrared spectroscopy (NIRS) prediction models...Cowpea (Vigna unguiculata L. Walp) is a multi-purpose legume with high quality protein for human consumption and livestock. The objective of this work was to develop near-infrared spectroscopy (NIRS) prediction models to estimate protein content in cowpea. A total of 116 cowpea breeding lines with a wide range of protein contents (19.28 % to 32.04%) were selected to build the model using whole seed and ground seed samples. Partial least-squares discriminant analysis (PLS-DA) regression technique with different pre-treatments (derivatives, standard normal variate, and multiplicative scatter correction) were carried out to develop the protein prediction model. Results showed: 1) spectral plots of both the whole seed and ground seed showed higher spectral scatter at higher wavelengths (>1450 nm), 2) data pre-processing affects prediction accuracy for bot whole seed and ground seed samples, 3) prediction using ground seed samples (0.64 R<sup>2</sup> 0.85) is better than the whole seed (0.33 R<sup>2</sup> 0.78), and 4) the data pre-processing second derivative with standard normal variate has the best prediction (R<sup>2</sup>_whole seed = 0.78, R<sup>2</sup>_ground seed = 0.85). The results will be of interest in cowpea breeding programs aimed at improving total seed protein content.展开更多
A quadrature modulator and an up-conversion mixer for an 802. lla wireless LAN system are designed and fabricated in 0.18μm gate length standard CMOS technology. A current feedback loop with a transconductor is used ...A quadrature modulator and an up-conversion mixer for an 802. lla wireless LAN system are designed and fabricated in 0.18μm gate length standard CMOS technology. A current feedback loop with a transconductor is used to improve the linearity of the quadrature modulator;An LC resonant tank is used as the load of the upconversion mixer to improve its gain and increase the voltage swing. The measurement results show that the input P1dB achieves -3.6dBm, the transducer power gain of the circuit is -3.6dB,and the current consumes about 45.8mA with a 1.8V power supply.展开更多
Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·（4.8-x） GdFy0.1NdF3.xYbF3·0.1TmF3 （x=-0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8） in molar ratio was deve...Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·（4.8-x） GdFy0.1NdF3.xYbF3·0.1TmF3 （x=-0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8） in molar ratio was developed. When the oxyfluoride glasses were heat-treated at the first crystallization temperature, the glasses gave transparent glass-ceramics in which rare earth containing fluorite-type nanocrystals of about 17.2 nm in diameter uniformly precipitated in the glass matrix. Compared with the glasses before heat treatment, the glass-ceramics exhibited very strong blue up-conversion luminescence under 800 nm light excitation. Rare earth containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass, the size of precipitated nanocrystals could be controlled by laser power and scan speed. The intensity of the blue up-conversion luminescence was strongly dependent on the precipitation of β-PbF2 nanocrystal and the YbF3 concentration. The reasons for the highly efficient Tm^3＋ up-conversion luminescence after laser irradiation were discussed.展开更多
Frequency up-conversion is an effective method of mid-infrared(MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light c...Frequency up-conversion is an effective method of mid-infrared(MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light carrying orbital angular momentum(OAM) from a difference frequency generation process and perform up-conversion on it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.展开更多
Er3 +/Yb3 +-codoped oxyfluoride crystallite glass was prepared with melting technique. The compositions and the melting temperature and the annealing temperature of the rare earth-doped crystallite glass were studied ...Er3 +/Yb3 +-codoped oxyfluoride crystallite glass was prepared with melting technique. The compositions and the melting temperature and the annealing temperature of the rare earth-doped crystallite glass were studied in detail. The emission spectra of samples were measured with the Hitachi F-4500 fluorescent photometer pumped by 980 nm wavelength laser. The up-conversion luminescence mechanism was illuminated on the view of the photophysics. By measuring the relationship between luminescent intensity and pump power, it is confirmed that the emission peaks at 550 nm belong to two-photon process, while that at 665 nm belongs to three-photon process. Moreover, the distributions of crystalline were determined by SEM.展开更多
The surface of an up-conversion luminescence material was modified by overcoating with SiOa, which was synthesized from a hydrolysis progress of telraethoxysilane （TEOS） in alkalescent condition. By analyzing the hy...The surface of an up-conversion luminescence material was modified by overcoating with SiOa, which was synthesized from a hydrolysis progress of telraethoxysilane （TEOS） in alkalescent condition. By analyzing the hydrolyzed mechanism of TEOS, it was found that there was not only physical adsorption but also chemical bonding between the up-conversion material and SiO2. At the same time, some adsorption bands at 1100, 475, 950, and 3500 cm^-1 were found by FI-IR, which were the characteristic bands of Si-OH and Si-O-Si. By analyzing the surface elements of the coated material by XPS, it was found that its surface only included Si, O, and C elements, and not F and Y. In the picture of XRD, there was no additional peak after surface modification, suggesting that the silica shell was amorphous. The small peak at 20 = 23° in the X-ray diffraction pattern of the coated material was caused by the amorphous SiO2 shell, and the TEM image also proved that the surface of the material was successfully modified by overcoating with SiO2. The amount of hydroxyls was then increased on the surface of the material, which made it easy to connect with other active groups.展开更多
The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time ...The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.展开更多
Er3＋/Yb3＋ co-doped Li3Ba2Gd3（MoO4）8 phosphors were synthesized by conven- tional solid state reaction method, and their structure and spectral properties were investigated. The diffuse reflectance spectra showed t...Er3＋/Yb3＋ co-doped Li3Ba2Gd3（MoO4）8 phosphors were synthesized by conven- tional solid state reaction method, and their structure and spectral properties were investigated. The diffuse reflectance spectra showed that the 4I15/2→4I11/2 transition of Er3＋ and the 2F7/2→2F5/2 transition of Yb3＋ ions were highly overlapped. Under the excitation of 980 nm, three up-conver- sion （UC） luminescence bands around 530, 555 and 660 nm were observed, corresponding to the 2H11/2→ 4I15/2, 4S3/2 → 4I15/2 and 4F9/2-→4I15/2 transitions of Er3＋ ions, respectively. The effects of the concentration and pumping power on the UC intensities of Li3Ba2Gd3（MoO4）8：Er3＋/yb3＋ phosphors were investigated, and the possible UC mechanism was proposed based on the results.展开更多
The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, h...The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, have been observed for the Er^3＋-doped silicate glass excited by a 978 nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296-673 K, which shows that Er^3＋-doped silicate glass can be used as a sensor in high-temperature measurement.展开更多
yb^3＋：Er^3＋ co-doped oxy-fluoride ceramics glass has been prepared. The mechanism of up-conversion emissions about Er^3＋ was discussed, and the temperature properties of green up-conversion fluorescence between 30...yb^3＋：Er^3＋ co-doped oxy-fluoride ceramics glass has been prepared. The mechanism of up-conversion emissions about Er^3＋ was discussed, and the temperature properties of green up-conversion fluorescence between 303 and 823 K were investigated. The results show that the sensitivity of this sample reaches its maximum value, about 0.0047 K^-1, when the temperature is 383 K, indicating that this kind of sample can be used as high temperature and high sensitivity optical temperature sensor.展开更多
Oxy-fluoride glasses with composition of 25SiO2-65PbF2-9.4AlF3-0.1HoF3-0.5YbF3 were prepared. Their up-conversion fluorescence characteristics were investigated by 980 nm laser. Two emission peaks were observed at 540...Oxy-fluoride glasses with composition of 25SiO2-65PbF2-9.4AlF3-0.1HoF3-0.5YbF3 were prepared. Their up-conversion fluorescence characteristics were investigated by 980 nm laser. Two emission peaks were observed at 540 and 650 nm. The up-conversion mechanism and processes were analyzed. The relationship between pumping power and relative intensity of emissions was discussed. From the dependence, it is known that the emissions centered at 540 and 650 nm are both attributed to two-photon process.展开更多
基金supported by the following research fundings including:the National Natural Science Foundation of China(Nos.62005114,62204078 and U22A2072)Natural Science Foundation of Henan-Excellent Youth Scholar(No.232300421092)Open Fund of the State Key Laboratory of Integrated Optoelectronics+(IOSKL2020KF01).
文摘Quantum dot-based up-conversion photodetector,in which an infrared photodiode(PD)and a quantum dot light-emitting diode(QLED)are back-to-back connected,is a promising candidate for low-cost infrared imaging.However,the huge efficiency losses caused by integrating the PD and QLED together hasn’t been studied sufficiently.This work revealed at least three origins for the efficiency losses.First,the PD unit and QLED unit usually didn’t work under optimal conditions at the same time.Second,the potential barriers and traps at the interconnection between PD and QLED units induced unfavorable carrier recombination.Third,much emitted visible light was lost due to the strong visible absorption in the PD unit.Based on the understandings on the loss mechanisms,the infrared up-conversion photodetectors were optimized and achieved a breakthrough photon-to-photon conversion efficiency of 6.9%.This study provided valuable guidance on how to optimize the way of integration for up-conversion photodetectors.
文摘Cowpea (Vigna unguiculata L. Walp) is a multi-purpose legume with high quality protein for human consumption and livestock. The objective of this work was to develop near-infrared spectroscopy (NIRS) prediction models to estimate protein content in cowpea. A total of 116 cowpea breeding lines with a wide range of protein contents (19.28 % to 32.04%) were selected to build the model using whole seed and ground seed samples. Partial least-squares discriminant analysis (PLS-DA) regression technique with different pre-treatments (derivatives, standard normal variate, and multiplicative scatter correction) were carried out to develop the protein prediction model. Results showed: 1) spectral plots of both the whole seed and ground seed showed higher spectral scatter at higher wavelengths (>1450 nm), 2) data pre-processing affects prediction accuracy for bot whole seed and ground seed samples, 3) prediction using ground seed samples (0.64 R<sup>2</sup> 0.85) is better than the whole seed (0.33 R<sup>2</sup> 0.78), and 4) the data pre-processing second derivative with standard normal variate has the best prediction (R<sup>2</sup>_whole seed = 0.78, R<sup>2</sup>_ground seed = 0.85). The results will be of interest in cowpea breeding programs aimed at improving total seed protein content.
文摘A quadrature modulator and an up-conversion mixer for an 802. lla wireless LAN system are designed and fabricated in 0.18μm gate length standard CMOS technology. A current feedback loop with a transconductor is used to improve the linearity of the quadrature modulator;An LC resonant tank is used as the load of the upconversion mixer to improve its gain and increase the voltage swing. The measurement results show that the input P1dB achieves -3.6dBm, the transducer power gain of the circuit is -3.6dB,and the current consumes about 45.8mA with a 1.8V power supply.
基金supported by the National Natural Science Foundation of China (50572029) Natural Science Foundation Project of Yunnan Province (2007E036M)
文摘Rare earth ions doped oxyfluoride glass with composition of 28SiO2·22AlO1.5·40PbF2·10PbO·（4.8-x） GdFy0.1NdF3.xYbF3·0.1TmF3 （x=-0, 0.1, 0.2, 0.5, 1, 2, 3, 4 and 4.8） in molar ratio was developed. When the oxyfluoride glasses were heat-treated at the first crystallization temperature, the glasses gave transparent glass-ceramics in which rare earth containing fluorite-type nanocrystals of about 17.2 nm in diameter uniformly precipitated in the glass matrix. Compared with the glasses before heat treatment, the glass-ceramics exhibited very strong blue up-conversion luminescence under 800 nm light excitation. Rare earth containing nanocrystals were also space selectively precipitated upon laser irradiation in an oxyfluoride glass, the size of precipitated nanocrystals could be controlled by laser power and scan speed. The intensity of the blue up-conversion luminescence was strongly dependent on the precipitation of β-PbF2 nanocrystal and the YbF3 concentration. The reasons for the highly efficient Tm^3＋ up-conversion luminescence after laser irradiation were discussed.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 92065101 and 11934013)Anhui Initiative In Quantum Information Technologies (Grant No. AHY020200)。
文摘Frequency up-conversion is an effective method of mid-infrared(MIR) detection by converting long-wavelength photons to the visible domain, where efficient detectors are readily available. Here, we generate MIR light carrying orbital angular momentum(OAM) from a difference frequency generation process and perform up-conversion on it via sum frequency conversion in a bulk quasi-phase-matching crystal. The maximum quantum conversion efficiencies from MIR to visible are 34.0%, 10.4%, and 3.5% for light with topological charges of 0, 1, and 2, respectively, achieved by utilizing an optimized strong pump light. We also verify the OAM conservation with a specially designed interferometer, and the results agree well with the numerical simulations. Our study opens up the possibilities for generating, manipulating, and detecting MIR light that carries OAM, and will have great potential for optical communications and remote sensing in the MIR regime.
文摘Er3 +/Yb3 +-codoped oxyfluoride crystallite glass was prepared with melting technique. The compositions and the melting temperature and the annealing temperature of the rare earth-doped crystallite glass were studied in detail. The emission spectra of samples were measured with the Hitachi F-4500 fluorescent photometer pumped by 980 nm wavelength laser. The up-conversion luminescence mechanism was illuminated on the view of the photophysics. By measuring the relationship between luminescent intensity and pump power, it is confirmed that the emission peaks at 550 nm belong to two-photon process, while that at 665 nm belongs to three-photon process. Moreover, the distributions of crystalline were determined by SEM.
基金the National Natural Science Foundation of China (Nos. 50372006, 20273007, and 20407003).
文摘The surface of an up-conversion luminescence material was modified by overcoating with SiOa, which was synthesized from a hydrolysis progress of telraethoxysilane （TEOS） in alkalescent condition. By analyzing the hydrolyzed mechanism of TEOS, it was found that there was not only physical adsorption but also chemical bonding between the up-conversion material and SiO2. At the same time, some adsorption bands at 1100, 475, 950, and 3500 cm^-1 were found by FI-IR, which were the characteristic bands of Si-OH and Si-O-Si. By analyzing the surface elements of the coated material by XPS, it was found that its surface only included Si, O, and C elements, and not F and Y. In the picture of XRD, there was no additional peak after surface modification, suggesting that the silica shell was amorphous. The small peak at 20 = 23° in the X-ray diffraction pattern of the coated material was caused by the amorphous SiO2 shell, and the TEM image also proved that the surface of the material was successfully modified by overcoating with SiO2. The amount of hydroxyls was then increased on the surface of the material, which made it easy to connect with other active groups.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074003 and 20973001)the Key Program of Educational Commission of Anhui Province of China (Grant No. KJ2010A132)
文摘The ultrafast carrier relaxation processes in CdTe quantum dots are investigated by femtosecond fluorescence upconversion spectroscopy.Photo-excited hole relaxing to the edge of the forbidden gap takes a maximal time of ～ 1.6 ps with exciting at 400 nm,depending on the state of the photo-excited hole.The shallow trapped states and deep trap states in the forbidden gap are confirmed for CdTe quantum dots.In addition,Auger relaxation of trapped carriers is observed to occur with a time constant of ～ 5 ps.A schematic model of photodynamics is established based on the results of the spectroscopy studies.Our work demonstrates that femtosecond fluorescence up-conversion spectroscopy is a suitable and effective tool in studying the transportation and conversion dynamics of photon energy in a nanosystem.
基金supported by the Natural Science Foundation of Shandong Province(ZR2014JL029,BS2015CL012,ZR2015BM005)
文摘Er3＋/Yb3＋ co-doped Li3Ba2Gd3（MoO4）8 phosphors were synthesized by conven- tional solid state reaction method, and their structure and spectral properties were investigated. The diffuse reflectance spectra showed that the 4I15/2→4I11/2 transition of Er3＋ and the 2F7/2→2F5/2 transition of Yb3＋ ions were highly overlapped. Under the excitation of 980 nm, three up-conver- sion （UC） luminescence bands around 530, 555 and 660 nm were observed, corresponding to the 2H11/2→ 4I15/2, 4S3/2 → 4I15/2 and 4F9/2-→4I15/2 transitions of Er3＋ ions, respectively. The effects of the concentration and pumping power on the UC intensities of Li3Ba2Gd3（MoO4）8：Er3＋/yb3＋ phosphors were investigated, and the possible UC mechanism was proposed based on the results.
基金Project supported by the National Natural Science Foundation of China (Grant No 60477023)the Natural Science Foundation of Science and Technology Commission of Liaoning Province, China (Grant No 20062137)
文摘The green and red up-conversion emissions centred at about 534, 549 and 663 nm of wavelength, corresponding respectively to the ^2H11/2 → ^4I15/2, ^4S3/2 → ^4I15/2 and ^4F9/2 → ^4I15/2 transitions of Er^3＋ ions, have been observed for the Er^3＋-doped silicate glass excited by a 978 nm semiconductor laser beam. Excitation power dependent behaviour of the up-conversion emission intensity indicates that a two-photon absorption up-conversion process is responsible for the green and red up-conversion emissions. The temperature dependence of the green up-conversion emissions is also studied in a temperature range of 296-673 K, which shows that Er^3＋-doped silicate glass can be used as a sensor in high-temperature measurement.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10804015 )the Science Foundation of the Education Department of Liaoning Province of China (Grant No. 2009A417)
文摘yb^3＋：Er^3＋ co-doped oxy-fluoride ceramics glass has been prepared. The mechanism of up-conversion emissions about Er^3＋ was discussed, and the temperature properties of green up-conversion fluorescence between 303 and 823 K were investigated. The results show that the sensitivity of this sample reaches its maximum value, about 0.0047 K^-1, when the temperature is 383 K, indicating that this kind of sample can be used as high temperature and high sensitivity optical temperature sensor.
文摘Oxy-fluoride glasses with composition of 25SiO2-65PbF2-9.4AlF3-0.1HoF3-0.5YbF3 were prepared. Their up-conversion fluorescence characteristics were investigated by 980 nm laser. Two emission peaks were observed at 540 and 650 nm. The up-conversion mechanism and processes were analyzed. The relationship between pumping power and relative intensity of emissions was discussed. From the dependence, it is known that the emissions centered at 540 and 650 nm are both attributed to two-photon process.
