Boosted UV emission on the optically and thermally stimulated luminescence of CaB6O10:Gd,Ag phosphors excited by X-rays

Abstract

The luminescent properties of X-ray phosphors based on optically stimulated luminescence (OSL) are quite fortuitous, since it demands the existence of both trapping and recombination (luminescent) centers. Nevertheless, lanthanide-doped materials have changed this paradigm by two main reasons: lanthanide doping provides the development of high efficient phosphors and allows for a relatively easy prediction of the energy-levels of the trapping centers involved in OSL phenomena. In view of that, this work reveals some luminescent and dosimetric properties of a phosphor never reported before, i.e., gadolinium and silver doped CaB6O10 polycrystalline samples. The phosphor synthesis followed a solid state reaction method and was optimized regarding the concentration of dopants for a better OSL response. Comparing to non-doped samples, the OSL showed an enhancement of ∼ 140x when doped with gadolinium and silver. The phosphor exhibited a high UV emission under blue stimulation (475 nm), with a linear dose-response for the range analyzed (1 mGy up to 2 Gy) and a minimum detectable dose of ∼ 40 μGy. The material exhibited a fading of ∼ 30% within the first 24 h after irradiation, which is attributed to shallow traps created by Ag+ incorporation. Wavelength-resolved thermoluminescence (TL) and OSL spectra revealed a sharp 317 nm emission, which is ascribed to 6PJ → 8S7/2 transition of Gd3+ centers, indicating that the Gd3+ has a crucial role in the luminescence mechanisms. In addition, the OSL spectrum exhibited also a broad emission at 350 nm attributed to 3DJ,1D2 → 1S0 transitions of Ag+ centers. Insights on the luminescent processes are given, including the role of Gd3+ and Ag+ centers in the trapping and recombination processes responsible for the TL and OSL. New mechanisms of luminescent enhancement by silver incorporation are suggested.