High-temperature diffusion doping as a method of fabrication of Ca3(VO4)2:Mn single crystals

Abstract

Calcium orthovanadate Ca3(VO4)2 crystals doped with manganese ions have been fabricated by high-temperature diffusion doping. Nominally pure CVO plates were prepared from the Czochralski grown single crystal. They were used as an effective matrix for diffusion impurity ions from solid phase (Mn2O3 powder) to solid phase (CVO single crystal). The high-temperature diffusion conditions were optimized to obtain the doped crystals of optical quality under using open and closed annealing zones. Diffusion coefficients of manganese ions were calculated for different conditions (temperature interval 1150–1300 °C, annealing time 24 h, 48 h, directions [001], [100]) of diffusion doping of CVO samples. The diffusion coefficient D varied from (3.7 ± 0.6) · 10−8 cm2s−1 at 1150 C up to (1.3 ± 0.2) · 10−7 cm2s−1 at 1300 C. The diffusion activation energy was determined to be 1.7 ± 0.4 eV and 3.3 ± 0.4 eV for the processes based on Fick’s laws during [100] and [001] direction, respectively. The ultimate solubility of manganese in CVO crystals at T = 1300 °C was 3 · 1020 cm−3. The absorption spectrum of diffusion doped Ca3(VO4)2:Mn samples is characterized by a combination of absorption bands specific for Mn2+, Mn3+ and Mn5+ ions. It was indicated that Mn5+ concentration in the diffusion doped CVO:Mn is higher than in CZ-grown Mn-doped materials.