Ho3＋/yb3＋ co-doped LiYF4 single crystals with various Yb3＋ concentrations and ,-~ 0.98 mol% Ho3＋ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a tem...Ho3＋/yb3＋ co-doped LiYF4 single crystals with various Yb3＋ concentrations and ,-~ 0.98 mol% Ho3＋ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient （40 ~C/cm-50 ~C/cm） for the solid-liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3＋ single-doped LiYF4 crystal, the Ho3＋/yb3＋ co-doped tiYf4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3＋ to Ho3＋ and the optimum fluorescence emission around 2.0 p-m of Ho3＋ ions are investigated. The maximum emission cross section of the above sample at 2.0 p.m is calculated to be 1.08 × 10-20 cm2 for the LiYF4 single crystal of 1-mol% Ho3＋ and 6-mo1% Yb3＋ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3＋ to Ho3＋ ion in the sample co-doped by Ho3＋ （1 mol%） and Yb3＋ （8 tool%） demonstrates that the Yb3＋ ions can efficiently sensitize the Ho3＋ ions.展开更多
The LiYF4 single crystal codoped with thulium and holmium ions was successfully grown by the Cz method. The optimal technical parameters obtained were as follows： the pulling rate was 0.16 mm/h; the rotation speed wa...The LiYF4 single crystal codoped with thulium and holmium ions was successfully grown by the Cz method. The optimal technical parameters obtained were as follows： the pulling rate was 0.16 mm/h; the rotation speed was 3 rpm; the cooling rate was 15 °C/h. The result of XRD curve showed that as-grown Tm,Ho：LiYF4 laser crystal belonged to the monoclinic system with scheelite-type structure and space group I41/a. The cell parameters calculated were： a=0.52160 nm, c=1.09841 nm and Z=4. Absorption and fluorescence spectra of Tm,Ho：LiYF4 laser crystal at room temperature were measured and analysed. The absorption cross section, FWHM and absorption coefficient at 779.3 nm calculated were 7.44×10–21 cm2, 8.7 nm and 2.23 cm–1, respectively. An intensive fluorescence emission peak appeared near 2045 nm. The emission cross section and fluorescence lifetime were 0.87×10–20 cm2 and 10.8 ms, respectively. The ratio of Tm–Ho transfer to its back-transfer process was 10.6.展开更多
The LiYF4 single crystals singly doped Ho3＋ and co-doped Ho3＋, Pr3＋ ions were grown by a modified Bridgman method. The Judd-Ofelt strength parameters （Ω2, Ω4, Ω6） of No3＋ were calculated according to the abso...The LiYF4 single crystals singly doped Ho3＋ and co-doped Ho3＋, Pr3＋ ions were grown by a modified Bridgman method. The Judd-Ofelt strength parameters （Ω2, Ω4, Ω6） of No3＋ were calculated according to the absorption spectra and the Judd-Ofelt theory, by which the radiative transition probabilities （A）, fluorescence branching ratios （β） and radiative lifetime （τ rad） were obtained. The radiative lifetimes of 5/6 and 5/7 levels in Ho3＋ （1 mol%）：LiYF4 are 10.89 and 20.19 ms, respectively, while 9.77 and 18.50 ms in Ho3＋/pr3＋ doped crystals. Hence, the τ rad of 5/7 level decreases significantly by introduction of Pr3＋ into Ho3＋：LiYF4 crystal which is beneficial to the emission of 2.9 μm. The maximum emission cross section of Ho3＋：LiYF4 crystal located at 2.05 μm calculated by McCumber theory is 0.51 ×10-20 cm2 which is compared with other crystals. The maximum emission cross section at 2948 nm in Ho3＋/pr3＋ co-doped LiYF4 crystal obtained by Fuchtbauer- Ladenburg theory is 0.68 × 10-20 cm2, and is larger than the value of 0.53 × 10-20 cm2 in Ho3＋ singly doped LiYF4 crystal. Based on the absorption and emission cross section spectra, the gain cross section spectra were calculated. In the Ho3- ions singly doped LiYF4 crystal, the gain cross sections for 2.05 μm infrared emission becomes positive once the population inversion level reaches 30%. It means that the pump threshold for obtaining 2.05 μm laser is probably lower which is an advantage for Ho3＋-doped LiYF4 2.05 μm infrared lasers. The calculated gain cross section for 2.9 μm mid-infrared emission does not become positive until the population inversion level reaches 40% in Ho3＋/pr3＋：LiYF4 crystal, but 50% in Ho3＋ singly doped LiYF4 crystal, indicating that a low pumping threshold is achieved for the H03＋：5/6 → 5/7 laser operation with the introduction of Pr3＋ ions. It was also demonstrated that Pr3＋ ion can deplete rapidly the lower laser Ho3＋：5/7 level and has influence on the Ho3＋：5/6 level. The Ho3＋/pr3＋：LiYF4 crystal may be a potential media for 2.9 μm mid-infrared laser.展开更多
The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is propo...The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51472125 and 51272109)the K.C.Wong Magna Fund in Ningbo University,China(Grant No.NBUWC001)
文摘Ho3＋/yb3＋ co-doped LiYF4 single crystals with various Yb3＋ concentrations and ,-~ 0.98 mol% Ho3＋ concentration are grown by the Bridgman method under the conditions of taking LiF and YF3 as raw materials and a temperature gradient （40 ~C/cm-50 ~C/cm） for the solid-liquid interface. The luminescent performances of the crystals are investigated through emission spectra, infrared transmittance spectrum, emission cross section, and decay curves under excitation by 980 nm. Compared with the Ho3＋ single-doped LiYF4 crystal, the Ho3＋/yb3＋ co-doped tiYf4 single crystal has an obviously enhanced emission band from 1850 nm to 2150 nm observed when excited by a 980-nm diode laser. The energy transfer from Yb3＋ to Ho3＋ and the optimum fluorescence emission around 2.0 p-m of Ho3＋ ions are investigated. The maximum emission cross section of the above sample at 2.0 p.m is calculated to be 1.08 × 10-20 cm2 for the LiYF4 single crystal of 1-mol% Ho3＋ and 6-mo1% Yb3＋ according to the measured absorption spectrum. The high energy transfer efficiency of 88.9% from Yb3＋ to Ho3＋ ion in the sample co-doped by Ho3＋ （1 mol%） and Yb3＋ （8 tool%） demonstrates that the Yb3＋ ions can efficiently sensitize the Ho3＋ ions.
基金Project supported by Changchun Science and Technology Bureau (2009110)Jilin Provincial Education Department (2009JYT15)Jilin Pro-vincial Science and Technology Department (20100556)
文摘The LiYF4 single crystal codoped with thulium and holmium ions was successfully grown by the Cz method. The optimal technical parameters obtained were as follows： the pulling rate was 0.16 mm/h; the rotation speed was 3 rpm; the cooling rate was 15 °C/h. The result of XRD curve showed that as-grown Tm,Ho：LiYF4 laser crystal belonged to the monoclinic system with scheelite-type structure and space group I41/a. The cell parameters calculated were： a=0.52160 nm, c=1.09841 nm and Z=4. Absorption and fluorescence spectra of Tm,Ho：LiYF4 laser crystal at room temperature were measured and analysed. The absorption cross section, FWHM and absorption coefficient at 779.3 nm calculated were 7.44×10–21 cm2, 8.7 nm and 2.23 cm–1, respectively. An intensive fluorescence emission peak appeared near 2045 nm. The emission cross section and fluorescence lifetime were 0.87×10–20 cm2 and 10.8 ms, respectively. The ratio of Tm–Ho transfer to its back-transfer process was 10.6.
基金supported by the National Natural Science Foundation of China(Grant Nos.51272109 and 50972061)the Natural Science Foundation of Zhejiang Province(Grant Nos.R4100364)the Natural Science Foundation of Ningbo City(Grant No.2012A610115)
文摘The LiYF4 single crystals singly doped Ho3＋ and co-doped Ho3＋, Pr3＋ ions were grown by a modified Bridgman method. The Judd-Ofelt strength parameters （Ω2, Ω4, Ω6） of No3＋ were calculated according to the absorption spectra and the Judd-Ofelt theory, by which the radiative transition probabilities （A）, fluorescence branching ratios （β） and radiative lifetime （τ rad） were obtained. The radiative lifetimes of 5/6 and 5/7 levels in Ho3＋ （1 mol%）：LiYF4 are 10.89 and 20.19 ms, respectively, while 9.77 and 18.50 ms in Ho3＋/pr3＋ doped crystals. Hence, the τ rad of 5/7 level decreases significantly by introduction of Pr3＋ into Ho3＋：LiYF4 crystal which is beneficial to the emission of 2.9 μm. The maximum emission cross section of Ho3＋：LiYF4 crystal located at 2.05 μm calculated by McCumber theory is 0.51 ×10-20 cm2 which is compared with other crystals. The maximum emission cross section at 2948 nm in Ho3＋/pr3＋ co-doped LiYF4 crystal obtained by Fuchtbauer- Ladenburg theory is 0.68 × 10-20 cm2, and is larger than the value of 0.53 × 10-20 cm2 in Ho3＋ singly doped LiYF4 crystal. Based on the absorption and emission cross section spectra, the gain cross section spectra were calculated. In the Ho3- ions singly doped LiYF4 crystal, the gain cross sections for 2.05 μm infrared emission becomes positive once the population inversion level reaches 30%. It means that the pump threshold for obtaining 2.05 μm laser is probably lower which is an advantage for Ho3＋-doped LiYF4 2.05 μm infrared lasers. The calculated gain cross section for 2.9 μm mid-infrared emission does not become positive until the population inversion level reaches 40% in Ho3＋/pr3＋：LiYF4 crystal, but 50% in Ho3＋ singly doped LiYF4 crystal, indicating that a low pumping threshold is achieved for the H03＋：5/6 → 5/7 laser operation with the introduction of Pr3＋ ions. It was also demonstrated that Pr3＋ ion can deplete rapidly the lower laser Ho3＋：5/7 level and has influence on the Ho3＋：5/6 level. The Ho3＋/pr3＋：LiYF4 crystal may be a potential media for 2.9 μm mid-infrared laser.
文摘The refractive index change and color centers formation in LiYF4 crystal at room temperature are induced by a femtosecond laser irradiation. A mechanism for refractive index change and color centers formation is proposed.
