以K_2O为助熔剂,应用坩埚下降法生长出了Co~(2+) 初始浓度为0.5 mol%,以及ZnO分别为3 mol%与6 mol%的单掺与双掺杂SLN晶体(分别用SLN0, SLN3, SLN6表示).测定了晶体上下部位的吸收与发射光谱.在晶体的吸收光谱中均可观察到520 nm,549 nm,612 nm,1447 nm四个吸收峰,表明Co~(2+)处于晶体的八面体场中.ZnO的掺入明显地改变了吸收峰的相对强度.在520 nm光的激发下,观察到776 nm的荧光发射,其荧光强度的相对强弱也与ZnO的掺杂量有明显的联系.从吸收边带估算出SLN0, SLN3, SLN6晶体中Li2O的含量分别为49.06 mol%,49.28 mol%, 49.10 mol%.ZnO的掺杂量对Co~(2+)在铌酸锂晶体中的浓度分布有很大的影响作用,当ZnO的掺入量为3 mol%时,明显地抑制了Co~(2+)在LiNbO_3晶体中的掺入,当ZnO掺杂量达到6 mol%时,抑制作用减弱.本文从Zn~(2+)在LiNbO_3中随浓度变化的分凝情况以及对Co~(2+)的排斥作用解释了Co~(2+)在晶体中的分布特性以及光谱的变化情况.
Near-stoichiometric LiNbO_3 single crystals doped with 0.5mol% Co~(2+) and co-doped with Co~(2+) in 0.5mol% and Zn~(2+) in 3 mol% and 6 mol% (designated SLN0, SLN3, SLN6, respectively) in the raw compositions were grown by the Bridgman method under the conditions of taking K_2O as flux. The absorption spectra and emission spectra of upper and lower parts of crystals were measured. The absorption spectra showed the characteristic of Co~(2+) in octahedral co-ordination, and four absorption peaks at 520 nm, 549 nm, 612 nm, 1447 nm were observed in all the obtained crystals. However, the absorption intensity had an obvious change with the content of ZnO dopant. A sharp emission peak at 776 nm was observed under excitation of 520 nm light, and the emission intensity was also associated with the doping content of ZnO. The contents of Li2O were estimated from the absorption edge of SLN0, SLN3 and SLN6 to be 49.06 mol%,49.28 mol% and 49.1 mol%. The doping content of ZnO takes great effects on the distributing concentration of Co~(2+) in LiNbO_3 crystal. When 3% of ZnO in mole fraction is doped, the Co~(2+) are suppressed effectively to enter LiNbO_3 crystal sites, and the effect becomes weaker while the dopant of ZnO reaches to 6% mole fraction. The reasons for the concentration changes of Co~(2+) and spectra change can be interpreted by the suppressing effect of ZnO on the incorporation of Co~(2+) ions and the change of distribution coefficient of Zn~(2+) as its incorporating content.
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