Babu Reddy J N, Ganesh Kamath K, Vanishri S, Bhat H L, Elizabeth Suja
Department of Physics, Indian Institute of Science, Bangalore 560012, India.
J Chem Phys. 2008 Jun 28;128(24):244709. doi: 10.1063/1.2943648.
Near-stoichiometric lithium niobate (SLN) crystals doped with up to 1.6 mol % Zn and codoped with various Nd concentrations in the melt (0.2, 0.5, 0.9, and 1.5 mol %) (Nd:Zn:SLN) are grown from 58.6 mol % Li(2)O using conventional Czochralski technique. Crystals are pulled at the rate of 0.35 mmh with seed rotation at 9 rpm. Concentrations of Zn and Nd in the crystal are varied by adding appropriate amounts of ZnO and Nd(2)O(3) to the starting composition. Unit cell parameters of the grown crystals are calculated by Rietveld refinement method using FULLPROFF software. Domain structure studies are carried out by chemical etching followed by microscopic examination. Dielectric studies reveal the existence of piezoelectric resonance at high frequencies. Enhancement in dielectric constant and tan delta in Nd doped samples has been attributed to the space charge polarization. Nd doped samples exhibit reduction in the relative permittivity after oxygen annealing. Transmission spectra of Nd:Zn:SLN crystals in the UV region exhibit blueshift in the cutoff wavelength. In Mid Infrared (MIR) region crystals doped with 1.6 mol % Zn have shift in the OH absorption peak from 2873 to 2833 nm. Judd-Ofelt analysis carried out on the absorption spectra of codoped crystal yields the lifetime of 104 mus for the metastable state (4)F(32). The branching ratio for the electronic transition from (4)F(32) to (4)I(112) is high compared to that for (4)F(32) to (4)I(132), indicating a higher emission cross section for the former transition. Laser damage threshold evaluated using 532 nm, 5 ns pulsed neodymium doped yttrium aluminum garnet laser, shows an increase by two orders of magnitude for crystals doped with 1.6 mol % Zn. Photorefractive damage threshold for these crystals shows an enhancement of four orders of magnitude due to increase in the photoconductivity.
采用传统的提拉法，从58.6摩尔%的Li₂O中生长出掺杂量高达1.6摩尔%的锌且在熔体中与不同浓度的钕（0.2、0.5、0.9和1.5摩尔%）共掺杂的近化学计量比铌酸锂（SLN）晶体（Nd:Zn:SLN）。晶体以0.35毫米/小时的速率提拉，籽晶转速为9转/分钟。通过向起始成分中添加适量的ZnO和Nd₂O₃来改变晶体中锌和钕的浓度。使用FULLPROFF软件通过Rietveld精修方法计算生长晶体的晶胞参数。通过化学蚀刻然后进行显微镜检查来进行畴结构研究。介电研究揭示了在高频下存在压电共振。钕掺杂样品中介电常数和损耗角正切的增强归因于空间电荷极化。钕掺杂样品在氧退火后相对介电常数降低。Nd:Zn:SLN晶体在紫外区域的透射光谱在截止波长处呈现蓝移。在中红外（MIR）区域，掺杂1.6摩尔%锌的晶体中OH吸收峰从2873纳米移至2833纳米。对共掺杂晶体的吸收光谱进行的Judd-Ofelt分析得出亚稳态⁴F₃/₂的寿命为104微秒。从⁴F₃/₂到⁴I₁₁/₂的电子跃迁分支比高于从⁴F₃/₂到⁴I₁₃/₂的分支比，表明前一种跃迁具有更高的发射截面。使用532纳米、5纳秒脉冲掺钕钇铝石榴石激光评估的激光损伤阈值表明，掺杂1.6摩尔%锌的晶体增加了两个数量级。由于光电导率增加，这些晶体的光折变损伤阈值提高了四个数量级。
