The Structure And Properties Research On Er:YbVO₄ Crystal

Because it combines semiconductor with solid, the laser diode pump solid-state laser(DPSSL) possess the merits of both semiconductor and solid.DPSSL has the properties of high pumping efficiency, stable output power and all solid state. DPSSL have found many important application fields e.g.in material processing.control and guide,medicine,optical communications ,laser display and laser nuclear fusion.So far as DPSSL is concerned, laser materials are important and they are the key factor for designing all solid-state lasers for DPSSL and decide the properties of lasers. Er:YbVO₄ crystal is also a laser crystal with excellent laser properties.Due to the erbium (Er) ion 1.5μm infrared emitting light good security and eye-safe, in the optical information, the optical communication, the medicine health and the national defense military , it has the very big potential application. The Yb ion has the extremely simple energy level structure (an excited state) and the energy gap is approximately 10000cm^-1, which is ideally suited for LD pumping near 976nm (commercialized),and it efficiently sensitizes the Er ion, thus it greatly reduces the doping density of the Er ion,and effectively reduces reabsorption at 1.5μm and avoids the quenching effect.Therefore we grew the Er:YbVO₄ crystal by using the Czochralski method. The Er:YbVO₄ crystal has the broad absorption band and high thermal conductivities. It is suitable for the high power laser application which is pumped by the laser diode. In a word, in this thesis, our work can be summarized by follows: 1. The YbVO₄ and Er:YbVO₄ crystals were grown by using the Czochralski method. The YbVO₄ and Er:YbVO₄ crystals are both the zircon crystals.The point group is 4/mmm, the space group is I4₁/amd.2.Based on the space group theory, the lattice vibration modes of YbVO₄ and Er:YbVO₄ are predicted.The YbVO₄ and Er:YbVO₄ crystals has the same structure .It comprise 4 units per cell,has 24 atoms and 72 lattice vibration modes.They were: Γ=5A_1g+2A_2g+2A_1u+7A_2u+7B_1g+2B_2g+2B_1u+5B_2u+10E_g+10E_u There are 72 modes, which equal to the movement degrees of freedom 72 of the 24 atoms. From the character table of the point group 4mmm, we know that 1A_2u and 1E_u are acoustical modes, 5A_1g, 7B_1g and 2B_2g are optical mode, 10E_g are dual degenerate mode,the others are dual degenerate optical modes.Theoretically,we can observe 32 active optical modes at the most from the crystal ,they areΓ_Vib= 5A_1g+7B_1g+2B_2g+10E_gwe determine the Raman scattering spectra of YbVO₄ and Er:YbVO₄ at room temperature by JASCONRS-1000DT micro Raman spectrophotometer, excellent agreement has been achieved between vibrational frequencies predicted by the theory and those observed in experiment. And we give some explain for that of Er:YbVO₄ crystal. 3. The thermal properties of Er:YbVO₄ single crystal were systemically studied, the specific heat was measured by the method of differential scanning calorimetry ,which value was 0.41Jg^-1 K^-1 at the temperature of 330K. The thermal expansion of Er:YbVO₄ single crystal was measured by using a thermal dilatometer and the average linear thermal expansion coefficient for all three crystallographic directions were calculated in the temperature range from 298.15K to 900K , which values areα_a= 4.244×10^-6/k, α_b=4.07834×10^-6/k, α_c=7.0×10^-6 /k. We analysis the anisotropic property of Er:YbVO₄ single crystal with structure feature of the crystal.we measured the thermal diffusion coefficient of Er:YbVO₄ single crystal and calculated the thermal conductivities of the crystal. At 303.15K, the thermal diffusion coefficients are 1.573mm²/s and1.956mm²/s along the Er:YbVO₄ single crystal [100] and [001] directions, the thermal conductivities are 3.87W/m·Kand 4.81W/m·K,correspondingly. The influences of these thermal properties on optical applications was analyzed.4.After be in go riented, cut and polished,The polarization and non-polarization absorption spectra and fluorescence spectra of the crystal were measured at room temperature.According to the absorption spectra, the phenomenological intensity parameters Ω of Er³⁺ ions have been fited based on the Judd-Ofelt theory. Moreover.the spectral parameters of Er³⁺ ions including radiative transition probabilities A_jj, oscillator strengths P_jj , radiative lifetime τ and integrated emission cross- section Σ have been calculated. From the parameters mentioned above, the laser emission probability of Er:YbVO₄ crystal was discussed.5. The Er:YbVO₄ crystal has the fine spectrum performance nearl.5jim. Chose the fine quality crystal to carry on the laser performance..But there was no laser, it produce 的 the fluorescence, we give explanation according to the energy level of the Er³⁺ ion.