Optical Spectroscopy of Pr3+ Ion Singly Doped LiLuF4 Single Crystal by Bridgman Method

High quality LiLuF4 single crystals doped with various Pr3+ ions were synthesized by a vertical Bridgman method in completely sealed platinum crucibles. The excitation spectra spans from 420 nm to 500 nm. The prepared single crystals exhibit a blue band at 480 nm(3P0→3H4), a green band at 522 nm (3P1→3H5), and a red band at 605 nm (1D2→3H4)when excited at 446 nm;their corresponding average lifetimes are 38.5μs, 37.3μs, and 36.8μs, respectively, which are much longer than those in oxide single crystals. The effects of excitation wavelength and doping concentration on emission intensities and chromaticity coordinates are investigated. The optimal Pr3+ concentration is confirmed to be 0.5%.The temperature dependent emission shows that the emission intensity constantly decreases with the increase of temperature from 298 K to 443 K due to the enhancement of nonradiative quenching at high temperature. The 3P0→3H4 transition is the most vulnerable to temperature, followed by the 3P1→3H5 transition and 1D2→3H4 transition.

Upconversion Luminescence from Ho3＋ and Yb3＋ Codoped α-NaYF4 Single Crystals

The Ho3＋/yb3＋ co-doped a-NaYF4 single crystal was grown successfully for the first time by a modified Bridgman method in which KF was used as assisting flux and a large temperature gradient （70-90℃ /cm） of solid-liquid interface was adopted. Upconversion emissions at green -544 nm, red -657 and -751 nm were obtained under 980 nm laser diode excitation. The intensity at -544 nm was much stronger than those of -657 and -751 nm. The mechanisms of the upconversion emissions were investigated by studying the relationship between the upconversion intensity and pump power. The optimized Yb3＋ concentration was about 8.08moi% when Ho3＋ concentration was hold at about 1.0mol%. The results showed that Ho3＋/yb3＋ doped α-NaYF4 single crystal was a possible candidate upconversion material for the green solid-state laser.

Luminescent Properties and Energy Transfer Mechanism of Gd^(3+) and Eu^(2+) Co-doped Phosphate Glasses

The phosphate glasses doped with Eu2＋, Gd3＋, respectively, and co-doped with Gd3＋ and Eu2＋ were prepared by high-temperature melting method. The transmission spectra, the excitation spectra, the emission spectra and the fluorescent decay time were investigated. The energy transfer process between Gd3＋ and Eu2＋ was studied. From the excitation spectra and the emission spectra of the phosphate glasses doped with Eu2＋, we observed that the emission intensity of Eu2＋ shows higher for 0.02 mol% Eu2＋-doped phosphate glass. According to the excitation spectra and the emission spectra and the fluorescence decay curves, when the concentration of Eu2＋ was 0.02 mol%, the optimal con- centration of Gd3＋ was 0.3 tool%. Based on Dexter theory, it is shown that the energy transfer between Gd3＋ and Eu2＋ was nonradiation energy transfer by analyzing the energy-level diagram. The fluorescence decay curves of Gd3＋ were expressed by the Inokuti-Hirayama＇s model and were used to analyze energy transfer mechanism between Gd3＋ and Eu2＋. And the energy transfer efficiency was also calculated.