Studies on luminescence properties and photo-thermo transfer phenomena in fluorapatite

Abstract

This study reports the structure, composition, photoluminescence (PL), thermoluminescence (TL), and optically stimulated luminescence (OSL) properties of the Brazilian natural fluorapatite. Also, the existence of photo-thermo transfer phenomena is investigated from TL/OSL emission mechanisms. X-ray diffraction (XRD) pattern reveals that the sample has a hexagonal system with a crystallite size of about 46 nm calculated using the Scherrer formula. The presence of several elements including the rare earths such as Ce, Nd, and Er are identified using total X-ray fluorescence (TXRF) spectroscopy results. Ce3+ ions are associated with the emission band at 371 nm when excited at 300 nm. Fluorapatite exhibits intense TL and OSL signals when irradiated with beta particles and shows linear dose-response from 1 up to 50 Gy. The TL glow curves are deconvoluted to six peaks centered at 99, 147, 188, 242, 329, and 431 °C using general order kinetic equation. The corresponding activation energies vary between 0.68 and 1.11 eV. An anomalous fading is noticed for the first TL peak, which decays completely in 6 h; the second TL glow peak decays about 59% within 12 h and other high temperature peaks are more stable. Continuous-wave OSL (CW-OSL) is constituted of three components, having decay times (τ) of 0.39, 5, and 64 s. The deconvoluted linearly modulated OSL (LM-OSL) has four peaks, with peak maxima (tm) at 2.85, 7.4, 27, and 130 s. Further, it is noticed the phenomenon of phototransferred TL (PTTL) at 30 °C, due to the optical transfer of electrons related to the traps of 329 and 431 °C peaks to the main peak at 242 °C. The temperature-induced PTTL using thermally assisted OSL (TA-OSL) at 170 °C with 400 s of blue stimulation depicted a transfer of trapped electrons from very deep traps (VDTs), located at temperatures higher than 500 °C, to the main peak. Here, the luminescence intensity increases with the beta dose.