Yanfu Lin

Radiative-trapping and fluorescence-concentration quenching effects of Yb:YAl 3 (BO 3 ) 4 crystals

The effects of radiative-trapping and fluorescence-concentration quenching on the emission spectra and fluorescence lifetimes of Yb3+-doped YAl3(BO3)4 crystals with a series of Yb3+ concentrations were studied. The shift of barycenters in emission spectra, Δλ, was proposed as an appraisement of the radiative-trapping effect on the spectra, and an empirical relation between Δλ and Yb3+ concentration in the Yb:YAl3(BO3)4 crystals was deduced. The model of excitation random walk was used to analyze the effects of radiative trapping and concentration quenching on the fluorescence lifetimes. The relation between fluorescence lifetime and Yb3+ concentration was obtained.

Novel Garnet-Structure Ca2GdZr2(AlO4)3:Ce3+ Phosphor and Its Structural Tuning of Optical Properties

Aluminate garnet phosphors Ca2GdZr2(AlO4)3:Ce(3+) (CGZA:Ce(3+)) for solid-state white lighting sources are reported. The crystal structure and Mulliken bonding population of the CGZA:Ce(3+) have been analyzed. The larger 5d ((2)D) barycenter shift εc and smaller phenomenological parameter 10Dq of Ce(3+) in CGZA are related to the larger covalent character of Ce-O. The tuning spectral properties of the Ce(3+)-doped CGZA-based isostructural phosphors are presented. The splitting of cubic crystal field energy level (2)Eg in Ca2REZr2(AlO4)3:Ce(3+) (CREZA:Ce(3+)) (RE = Lu, Y, and Gd) increases as the radius of RE(3+) increases, and the splitting of (2)Eg may dominate the difference of spectroscopic red-shift D(A) in CREZA:Ce(3+). The splitting of the (2)Eg in CaGd2ZrSc(AlO4)3:Ce(3+) (CGZSA:Ce(3+)) phosphors increases seemly due to the decreasing of the covalent character of Ce-O. Thermal quenching properties of Ce(3+)-doped CGZA-based isostructural phosphors are also presented and analyzed. For CREZA:Ce(3+) phosphors, the increasing of the radius of RE(3+) results in an enhancement of thermal quenching. The quenching of CGZSA:Ce(3+) is obviously stronger mainly due to the smaller energy difference between the lowest 5d excited state and 4f ground state.

Spectroscopic analysis and laser performance of Tm3+ : NaGd(MoO4)2 crystal

Detailed polarized spectral properties of Tm3+ : NaGd(MoO4)2 crystal have been investigated. The room temperature absorption and fluorescence spectra were recorded. The fluorescence decay mechanisms of the 1G4 and 3H4 multiplets in Tm3+ : NaGd(MoO4)2 crystal were discussed. Room temperature quasi-cw 1.9 µm laser emission from the Ti : sapphire laser pumped Tm3+ : NaGd(MoO4)2 crystal has been demonstrated. The maximum output power of 170 mW has been achieved with a slope efficiency of 25%.

Enhanced efficiency of Er:Yb:Ce:NaGd(WO 4 ) 2 laser at 1.5–1.6 μm by the introduction of high-doping Ce 3+ ions

By the introduction of high-doping Ce3+ ions, the upconversion fluorescence of Er3+ ions was reduced, and the energy-transfer efficiency from Yb3+ to Er3+ ions was enhanced significantly in Er:Yb:Ce:NaGd(WO4)2 crystals. End pumped by a diode laser at 970 nm in a hemispherical cavity, a 2.0 W quasi-cw laser at 1.5-1.6 microm with slope efficiency of 19% and absorbed pump threshold of 2.0 W was achieved in a 1.7-mm-thick c-cut Er:Yb:Ce:NaGd(WO4)2 crystal. The results show that the Er.:Yb:Ce:NaGd(WO4)2 crystal with high-doping Ce3+ ions is a potential gain medium for a low-threshold 1.5-1.6 microm laser.

Polarized spectral properties and laser demonstration of Tm3+-doped LiGd(MoO4)(2) crystal

Trivalent thulium-doped LiGd(MoO4)2 single crystals have been grown by the Czochralski method. Room-temperature polarized absorption and fluorescence spectra of the crystals were analyzed. The fluorescence decay curves of the 1G4, 3H4, and 3F4 multiplets were measured, and the decay mechanisms of the 1G4 and 3H4 multiplets were discussed. Spectroscopic parameters related to the laser operation around 1.90 μm via the 3F4→3H6 transition have been evaluated. Finally, end-pumped by a Ti:sapphire laser at 795 nm, the room-temperature quasi-continuous wave 1.9 μm laser emission was demonstrated with a slope efficiency of 28%.

Energy transfer in Yb3+-Er3+-codoped bismuth borate glasses

The mechanism of energy transfer from Yb3+ to Er3+ ions has been studied in bismuth borate glasses with a serial Yb3+ concentration. The analysis of the donor fluorescence decay with a low concentration has been used to determine the multipole character of the energy transfer. The energy-transfer microparameters were determined and used to calculate the migration-assisted energy-transfer rates on the basis of the hopping model, which are in agreement with those obtained by fitting the fluorescence decay curves. An efficient energy transfer from Yb3+:2F5/2 to Er3+:I11/2 in the bismuth borate glasses has been demonstrated.

Spectroscopic and laser properties of Er 3+ :Yb 3+ :LuAl 3 (BO 3 ) 4 crystal at 1.5-1.6 μm

An Er(3+):Yb(3+):LuAl(3)(BO(3))(4) crystal doped with 24.1 at.% Yb(3+) and 1.1 at.% Er(3+) ions was grown by the flux method. The polarized spectroscopic properties related to the operation of 1.5-1.6 microm laser of the crystal were evaluated at room temperature. The laser properties of a 0.7-mm-thick, c-cut crystal were investigated in diode-end-pumped hemispherical and plano-plano cavities, respectively. Compared with those of Er(3+):Yb(3+):YAl(3)(BO(3))(4) crystal obtained under similar experimental conditions, higher maximum output peak power, higher slope efficiency, and lower threshold were achieved in the Er(3+):Yb(3+):LuAl(3)(BO(3))(4) crystal.

High efficient 1.56 µm laser operation of Czochralski grown Er:Yb:Sr3Y2(BO3)4 crystal

An Er:Yb:Sr(3)Y(2)(BO(3))(4) crystal doped with 0.9 at.% Er(3+) and 18.6 at.% Yb(3+) ions was grown by the Czochralski method. End-pumped by diode laser at 970 nm in a hemispherical cavity, 1.3 W quasi-cw laser output around 1.56 microm was achieved in a 1.1-mm-thick Z-cut Er:Yb:Sr(3)Y(2)(BO(3))(4) crystal when the transmission of output coupler is 1.5%. The absorbed pump threshold and slop efficiency of the laser are 4.26 W and 20%, respectively. This crystal has flat and broad gain curve peaked around 1.56 microm, which shows that it is also a potential gain medium for tunable and short pulse lasers.

Tm 3+ /Ho 3+ co-doped LiGd(MoO 4 ) 2 crystal as laser gain medium around 2.0 μm

Tm3+/Ho3+ co-doped LiGd(MoO4)2 (LGM) crystals were investigated as gain media for the Ho3+ laser around 2.0 μm. Polarized spectroscopic parameters of Ho3+ ions in the crystals were calculated based on the absorption spectra by the Judd-Ofelt theory. Related fluorescence spectra and decay curves were measured and analyzed for the crystals with different Tm3+/Ho3+ co-doped concentrations, 5.4/1.4 and 4.6/0.6 at.%. Stimulated emission cross sections of the 5I7→5I8 transition of Ho3+ ions were derived according to the Fuchtbauer-Ladenburg formula. End-pumped by a pulsed diode laser at 795 nm, the Ho3+ laser at 2.05 μm with a slope efficiency of 20% was realized in a c-cut crystal sample with the Tm3+/Ho3+ concentrations of 4.6/0.6 at.%.

Growth, spectral properties, and laser demonstration of Yb3+:BaGd2(MoO4)4 cleavage crystal

Detailed polarized spectral properties of a 3.6 at. % Yb3+:BaGd2(MoO4)4 (Yb3+:BGM) cleavage crystal grown by the Czochralski method have been investigated, including the absorption cross section, the emission cross-section, and the fluorescence lifetime. The evaluation of the laser potentiality shows that the Yb3+:BGM crystal is promising for tunable and ultrashort laser generations around 1 μm. The room temperature quasi-CW laser operation of an unprocessed 3.6 at. % Yb3+:BGM cleavage plate has been demonstrated with diode pumping. The results indicate that the Yb3+:BGM crystal is a good candidate for microchip laser gain medium by cleavage technique.