Growth of Mn2+, Co2+ and Ni2+-doped near-stoichiometric LiNbO3 by Bridgman method using K2O flux

The near-stoichiometric LiNbO3 (SLN) single crystals doped Mn2+, Co2+ and Ni2+ in 0.5 mol% concentration in the raw compositions were grown by the Bridgman method under the conditions of taking K2O as flux, a high temperature gradient (90–100 °C/cm) for solid–liquid interface. The XRD, absorption spectra, excitation spectra and emission spectra have been carried out. From the absorption edges of Mn2+, Co2+ and Ni2+-doped SLN crystals, the molar ratio of [Li+]/[Nb5+] are estimated to be about 0.977. The absorption spectra of Mn2+:SLN have shown a broad absorption band centered at ∼571 nm (6A1g(6S) → 4T1g(4G)), three absorption peaks at 520, 549 and 612 nm (overlapping of the 4T1(F)–4A2(F), 4T1(F)–4T1(P)), and a wide absorption band at 1400 nm (4T1(F) → 4T2(F)) of Co2+:SLN, Ni2+:SLN, and five absorption peaks at 381 nm (3A2g(F) → 3T1g(P)), 733 nm (3A2g(F) → 3T1g(F)), 1280 nm (3A2g(F) → 3T2g(F)), 430 nm (3A2g(F) → 1T2g(D)), and 840 nm (3A2g(F) → 1E(D)) of Ni2+:SLN were observed. A red emission at 612 nm (4T1g(4G) → 6A1g(6S)) for Mn2+:SLN, a red emission at 775 nm (4T1(P) → 4T1(F)) for Co2+:SLN, and a green emission at 577 nm (1T2g(D) → 3A2g(F)) and a red emission at 820 nm (1T2g(D) → 3T2g(F)) for Ni2+:SLN were observed under excited by 416, 520 and 550 nm lights, respectively. The concentration distribution of Mn2+, Co2+and Ni2+ ion in SLN crystals was investigated primarily from the absorption and emission spectra for various parts. The effective distribution coefficient for Mn2+ was less than 1. While, for Co2+ and Ni2+ were more than 1.