Ni^(2+)掺杂近化学计量比铌酸锂晶体的生长及光谱特性

Growth and Optical Properties of Near-Stoichiometric Ni^(2+)-Doped Lithium Niobate Crystal

以K2O为助熔剂,在较大的固液界面温度梯度条件下,应用坩埚下降法技术生长了初始Ni2+掺杂摩尔分数为0.5%的近化学计量比铌酸锂晶体。测定了晶体的吸收光谱,观测到由Ni2+离子在八面体中3A2g(F)→3T1g(P)、3A2g(F)→3T1g(F)、3A2g(F)→3T2g(F)能级的正常自旋允许跃迁所产生的381 nm,733 nm,1280 nm吸收峰和3A2g(F)→1T2g(D)和3A2g(F)→1E(D)能级的自旋禁戒跃迁产生的430 nm与840 nm吸收峰。从晶体紫外吸收边的位置初步估算其摩尔分数比x(Li+)/x(Nb5+)为0.981。根据晶体分裂场理论和吸收光谱,计算了Ni2+在该铌酸锂晶体中的晶格场分裂参量Dq=781 cm-1、Racah参量B=1096 cm-1与C=4353 cm-1。研究了在不同激发波长下晶体在可见光波段的荧光特征,观察到500~630 nm的绿色与800~850 nm的红色荧光发射带,它们归结为1T2g(D)→3A2g(F)与1T2g(D)→3T2g(F)的能级跃迁所致。

The near-stoichiometric LiNbO3 （SLN） single crystals doped Ni^2＋ in 0.5% molar fraction in the raw compositions were grown by the Bridgman method under the conditions of taking K2O as flux and at a big temperature gradient for solid-liquid interface. The absorption spectrum of Ni^2＋ doped crystal was measured. The 381 nm, 733 nm and 1280 nm, which are ascribed to spin allowed ^3A2g （F）→^3T1g （P）, ^3A2g （F）→^3 T^g （ F）, ^3A2g （F）→^3T2g （F） transitions of Ni^2＋ ions in octahedral co-ordination, and 430 nm and 840 nm, which are attributed to spin forbidden ^3A2g （F）→^1T2g （D） and ^3A2g （F）→^1E （ D ） transitions, were observed. The molar fraction ratio of x（Li^＋ ）/x（Nb^5＋） was estimated from the absorption edge of the crystal to be 0. 981. The crystal field strength of Ni^2＋ doped in SLN crystal, Dq =781 cm^-1 , the Racah parameter B=1096 cm^-1 and C=4353 cm^-1 were calculated from the absorption spectrum and crystal splitting theory. The emission spectra of crystal in the visible region were investigated under various light excitation, and the emission bands at 500-630 nm, 800~850 nm were observed and ascribed to the d- d transition ^1T2g （D）→^3A2g （F）, ^1T2g （D）→^3 T2g （F） of Ni^2＋ in octahedral sites, respectively.