Study On Growth And Properties Of Er:Lu_xgd_1-xVO₄Series Laser Crystals

Laser crystals doped with different stimulated rare earth elements are important for many optical applications, especially as laser host, polarizer and phosphor. Vanadatfamiy crystal is a kind of attractive laser hosts for diode-laser pumped all solid state lasers, which make lasers to low threshold, high slope efficiency and compactness in size. Among rare earth active laser ions, erbium is of special interest because Er3+doped vanadate crystals generate two important laser emissions:4I13/2�'4I15/2and4I11/2�'4I13/2, at around1.5and3.0μm which are useful for high speed optical fiber communication systems and gas sensing application respectively. Compared with other vanadate crystals, Er:GdVO4has a large thermal conductivity along the c-axis directions [2] and the crystal-field splitting of the4I15/2level of Er3+in Er:LuVO4is slightly higher than those in the Er:YVO4and Er:GdVO4crystals [3]. LuVO4and GdVO4possess the same ZrSiO4structure, belonging to the tetragonal symmetry space group I41/amd, and their melting points are very close (～1800℃). These features enable the LuVO4-GdVO4mixed vanadate crystals to be grown as a solid solution system.1. Crystal growthA new series Er:LuxGd1-xVO4mixed laser crystals have been successfully grown by the Czochralski methods with1%Er concentration in the Er:LuxGd1-xVO4melt. Where x=0.1,0.24,0.48,0.57,0.79and0.9. In the growth process, V2O5, Lu2O3, Er2O3and Gd2O3powders with purity of99.99%were used as the raw Materials. Polycrystalline ErVO4and LuVO4and GdVO4were synthesized by the liquid-phase method. The factors related to the growth progress and quality of crystals were analyzed systematically based on the therories of thermodynamics and dynamics. The suitable temperature field, reasonable growing procedure, crystal seed with excellent quality is used. Raw materials and polycrystalline synthesized by the liquid-phase method with excellent quality are referred to such factors. The corresponding measures related to these factors appeared in crystal growth process were also presented for high quality crystal gowth.2. Structure and quality of Er:LuxGd1-xV04The structures of the as-grown Er:LuxGd1-xVO4crystals were determined by X-ray powder diffraction (XRPD). The XRPD results show that the as-grown crystals belong to the tetragonal crystal system with a space group of I41/amd. The lattice were calculated by the DICVOL program. The density(p) of Er:LuxGd1-xVO4with different x were measured by buoyancy method at room temperature. The quality of the as-grown Er:LuxGd1-xVO4crystals were characterized by high-resolusion X ray diffraction and chemical etching methods. The results show that the as-grown Er:LuxGd1-xVO4crystals with different x are of excellent quality, the main defects in these crystals are dislocation and grain boundary. For improving the crystal quality we came up with a series of measures, based on the defect formation mechanism.3. Thermal properties of Er:LuxGd1-xVO4crystalsThe thermal properties of Er:LuxGd1-xVO4crystals series crystals were investigated systematically, the influence of these properties on crystal growth and applications was also discussed.The special heat of Er:LuxGd1-xVO4crystals were measured from room temperature to300℃by differential thermal scanning calorimeter. Whereby the Constant molar heat capacity increased initially then reduced along with the x increased. But at normal temperatures it always bigger than Er:YVO4. At the room temperature, the heat capacity values in between0.497-0.578J/g·k for different components Er:LuxGd1-xVO4crystals. The molar heat capacities were measured by thermal dilatometer of different components Er:LuxGd1-xVO4crystals between30～500℃. The different components of the series of crystals, the thermal expansion coefficient were greater than a to c. Along with the components of Lu and Gd tend to consistent, the thermal expansion coefficient both tend to smaller along with a and c. In303.15～573.15K temperature range, the thermal diffusion coefficients of different components Er:LuxGd1-xVO4crystals with x=0.1,0.24,0.48,0.57,0.79,0.9were measured by laser pulse method. At room temperature, the thermal diffusion coefficients were X33=2.252,2.057,1.802,1.805,2.001,2.039与λ11=2.027,1.873,1.594,1.609,1.768,1.807with x=0.1,0.24,0.48,0.57,0.79,0.9respectively. The thermal conductive of different components Er:LuxGd1-xVO4crystals were calculated by the relevant formula. The results show that along with the components of Lu and Gd tend to consistent the value will become smaller.4、Optical properties of Er:LuxGd1-xVO4crystalsFor the vanadate crystals, they are the primary materials in the diode pumped solid state laser with middle to low output power, because of their large absorb and emission cross section. However, the relatively largr emission cross section and short up-level lifetime have constrained their application in Q-swiched lasers because it requires a large energy storagecapacity. We measured the Er:LuxGd1-xVO4crystals’ absorption spectrum and fluorescence spectrum with different x. The spectral parameters were calculated by J-O theory. The results shows that because of caused by the inhomogeneous spectrum broadening of Er3+ions in the mixed crystals, the stimulated emission cross sections decreased and fluoresces lifetime increased in the mixed crystals, which can enhance the energy storage capacity. In the Er3+doped Er:LuxGd1-xVO4mixed crystals, due to the random placement of different cations in the lattice, the spectra are inhomogeneously broadened, as the degree of molecular chaos lager, the spectrum width turned lager and lifetime turned longer.The temperature dependent fluorescence properties of Er:Luo.57Gdo.43V04mixed crystal were investigated in the temperature range of78to296K and the1.5μm band. The fluorescence lifetime and emission cross sections were achieved at different temperature. The inhomogeneous broadening in the spectra was discussed based on the random replacement of Lu3+and Gd3+ions in the same sites. The results indicate that the Er:Luo.57Gdo.43V04crystal possesses a large energy storage property and should be suitable for the pulsed lasers with high energy.