Influence of charge compensators on the photoluminescence and thermoluminescence of CaSO4:Tb,A (A=Na, K, Rb, F, Cl, Br) phosphors

Abstract

The influence of charge compensators on the luminescence properties of Tb-doped anhydrite CaSO₄ powders was studied for 9 phosphors synthesized by solid-phase reactions from the starting materials CaSO₄, (NH₄)₂SO₄, Tb₄O₇ or TbCl₃, MeCl (Me = K, Na, Rb), or NaHal (Hal = F, Cl, Br). A comprehensive analysis of the luminescence excitation spectra in the 4.8–45 eV region for the blue luminescence (BL) and green luminescence (GL) series of Tb³⁺ ions was performed. It was shown that the intensity of Tb³⁺ emission increases as the ionic radius of the charge-compensating Me ion decreases. The GL/BL ratio depends on the charge compensator and excitation energy and is determined by the relative concentrations of complex terbium centers containing at least two terbium ions and single Tb³⁺ ions. It was shown that the CaSO₄ phosphor synthesized from Tb₄O₇ and NaCl starting materials is the most efficient phosphor for spectral converters. The absence of charge compensating ions gives rise to a deep trapping centers related to cation vacancies. Based on analysis of the thermally stimulated luminescence curves, the CaSO₄:TbCl₃ phosphor is considered the most promising for dosimetry.