Pure and Tm3+-doped Ca3(VO4)2 crystals: Growth, statistical and local structure, and luminescent properties

Abstract

Pure and Tm3+-doped Ca3(VO4)2 crystals (CVO and CVO:Tm) were grown by the Czochralski method. Activator ions were introduced in the form of Tm2O3 (0.5 and 1.0 wt%) over CVO stoichiometry. The single-crystal X-ray diffraction analysis revealed for the first time the actual crystal compositions with a splitting of one Ca5 site into two, Ca5 and Ca5A, defective sites and a partial occurrence of Tm3+ ions in two, Ca3 and Ca4, sites. X-ray absorption spectroscopy showed that the Tm3+ ions have octahedral coordination with an additional oxygen atom (coordination number, 6 + 1) and the V5+ ions have tetrahedral coordination (coordination number, 4). The structure of CVO:Tm crystals is proposed based on the local structure of Tm3+ ions, taking into account their structural organization in Tm2O3 and structural features of the CVO crystal matrix. Spectral-luminescent properties of CVO:1.0 wt%Tm crystal are consistent with structural results obtained: two pronounced peaks at λ = 470.5 and 473.5 nm in the absorption spectra (77 K), two different fluorescence spectra for different excitation wavelengths, and two components with significantly different lifetimes (1380 and 370 μs) in the decay curves indicate the presence of two different Tm3+ optical centers in the Ca3(VO4)2 crystal with excellent spectroscopic properties.