White light emission from Dy3+-doped LiLuF4 single crystal grown by Bridgman method

Lithium lutetium fluoride （LiLuF4） single crystals doped with different Dy3＋ ion concentrations were grown by Bridgman method. The Judd-Ofelt （J-O） strength parameters （Ω2, Ω4, Ω6） of Dy3＋ in LiLuF4 crystal are calculated according to the measured absorption spectra and the J-O theory, by which the asymmetry of the Dy3＋：LiLuF4 single crystal and the possibility of attaining stimulated emission from 4F9/2 level are analyzed. The capability of the Dy3＋：LiLuF4 crystal in generating white light by simultaneous blue and yellow emissions under excitation with ultra- violet light is produced. The effects of excitation wavelength and doping concentration on chromaticity coordinates and photoluminescence intensity are also investigated. Favorable CIE coordinates, x=0.319 3 and y=0.349 3, can be obtained for Dy3＋ ion in 2.701% molar doping concentration under excitation of 350 nm.     

Tunable emission,concentration quenching and crystallographic sites of Eu^2＋ in Sr3Y（PO4）3

A series of Sr3Y（PO4）3：Eu^2＋ samples are synthesized by the high temperature solid-state method. Sr3Y（PO4）3：Eu^2＋shows an asymmetrical emission band under excitation of 350 nm. The emission peaks at 426 nm and 497 nm are assigned to the nine-coordination Eu^2＋ and six-coordination Eu^2＋, respectively. The effects of Eu^2＋ doping content on the emission intensity and color are observed, and the concentration quenching effect is also observed. For two different Eu^2＋ luminescence centers, the quenching mechanisms are dipole-dipole interaction and quadrupole-quadrupole interaction, respectively. And the critical distance of energy transfer is calculated by concentration quenching and turns out to be about 3.67 nm. The results above show that the asymmetrical emission band of Sr3Y（PO4）3：Eu^2＋ comes from two different Eu2＋ luminescence centers in the lattice.     

日本红外光纤的进展

红外光纤由于其广泛的应用领域而具有很大的吸引力，现今无论在制备技术还是在光学损耗及结构特征等物理化学性能分析上都取得引人注目的进展。红外光纤可能发展为在中红外区域工作的超低损耗通讯用光纤，这就引起了研究者的兴趣。尽管为此目的还发展了如卤化物晶体和硫系玻璃等许多材料，但人们仍倾向于根据其应用范围来选择红外光纤材料。     

BiCl_3-KCl-As_2S_3系玻璃的形成、性质和结构

报道了BiCl_3-KCl-As_2S_3系玻璃的形成。以BiCl_3和As_2S_3为基础的玻璃的红外透过率直到11μm以后才开始下降,这对CO_2激光(10.6μm)传输非常有利。在BiCl_3-KCl系中引入As_2S_3可显著改善玻璃的化学稳定性。根据喇曼光谱结果,分别研究了BiCl_3-KCl系全氯化物玻璃及BiCl_3-KCl-As_2S_3混合系玻璃的结构。     

Enhanced emission at 2.85 μm of Ho3+/Pr3+ co-doped α-NaYF4 single crystal

The Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystals with various Pr³⁺ concentrations and constant Ho³⁺ molar percentage of ~1% were grown by an improved Bridgman method. Compared with the Ho³⁺ single-doped NaYF₄ crystal, an obviously enhanced emission band at 2.85 μm is observed under 640 nm excitation. The Judd-Ofelt strength parameters (Ω ₂, Ω ₄ and Ω ₆) are calculated, the radiative transition probabilities (A), the fluorescence branching ratios (β) and the radiative lifetime (τ _rad) are obtained in the meantime. The energy transfer from Pr³⁺ to Ho³⁺ and the optimum fluorescence emission of Ho³⁺ ions around 2.85 μm are investigated. Moreover, the maximum emission cross section of above samples at 2.85 μm is calculated to be 0.72×10^-20 cm² for the NaYF4 single crystal with Ho³⁺ molar percentage of 1% and Pr³⁺ molar percentage of 0.5% according to the measured absorption spectrum. All results suggest that the Ho³⁺/Pr³⁺ co-doped NaYF₄ single crystal may have potential applications in mid-infrared lasers.     

Growth and optical properties of Dy3+/Eu3+ co-doped NaYF4 single crystals with cubic lattice for white LED application

Dy3+/Eu3+ co-doped cubic lattice NaYF4 single crystal with high quality in the size of ~Φ1.0 cm×10.0 cm was grown by an improved Bridgman method using potassium fluoride (KF) as assistant flux. X-ray diffraction (XRD), absorption spectra, excitation spectra and emission spectra are measured to investigate the phase and luminescent properties of the crystal. The effects of excitation wavelength and concentrations of Dy3+ and Eu3+ ions on the luminescent characteristics are analyzed. The NaYF4 single crystal with the doping molar concentrations of 1.205% Dy3+ and 0.366% Eu3+ exhibits an excellent white light emission with chromaticity coordinates of x=0.321, y=0.332. It indicates that the Dy3+/Eu3+ co-doped cubic lattice NaYF4 single crystal can be a potential luminescent material for the ultraviolet (UV) light excited white light emitting diode (w-LED).     

Spectral properties and energy transfer in Er3+/Yb3+ co-doped LiYF4 crystal

Laser crystals of LiYF4 (LYF) singly doped with Er3+ in 2.0% and co-doped with Er3+/Yb3+ in about 2.0%/1.0% molar fraction in the raw composition are grown by a vertical Bridgman method. X-ray diffraction (XRD), absorption spectra, fluorescence spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. Compared with the Er3+ singly doped sample, obviously enhanced emission at 1.5 μm wavelength and green and red up-conversion emissions from Er3+/Yb3+ co-doped crystal are observed under the excitation of 980 nm laser diode. Meanwhile, the emission at 2.7 μm wavelength from Er3+ singly doped crystal is reduced. The fluorescence decay time ranging from 18.60 ms for Er3+ singly doped crystal to 23.01 ms for Er3+/Yb3+ co-doped crystal depends on the ionic concentration. The luminescent mechanisms for the Er3+/Yb3+ co-doped crystals are analyzed, and the possible energy transfer processes from Yb3+ to Er3+ are proposed.