Size effects and radiation resistance of BaF2 nanophosphors

Abstract

Abstract The stationary X-ray excited luminescence (XEL) spectra at 80 and 294 K as well as the thermally stimulated luminescence (TSL) in the 80–300 К range of a single crystal and nanoparticles of BaF2 with various grain sizes of 20–113 nm were studied. Under the influence of size effects in BaF2 nanophosphors, a short-wave displacement of self-trapped excitons emission band was observed compared to the corresponding single crystal, and its splitting into two components peaked at 324 and 305 nm for 294 K, and at 321 and 305 nm – for 80 K. A slight decrease of radiation resistance of BaF2 nanophosphors was observed in comparison to single crystal, which led to additional band of X-ray excited luminescence at ∼410 nm that may be associated with emission of exciton localized in the vicinity of anionic vacancies of the matrix. At the same time, it was established that radiation resistance of BaF2 nanophosphors is much higher compared to the corresponding CaF2 nanophosphors. With the use of integral TSL curves and TSL spectra, it has been shown that VH-centers with delocalization temperature of ∼140 K are the main hole centers that occur in BaF2 nanoparticles under X-ray irradiation influence, while in ВаF2 single crystals – these are Vk - and H-centers with delocalization temperatures at 113 and 198 К, respectively. Significant long-wave displacement of emission bands associated with (VH-F)- and (H-F)- recombinations, compared to the spectra of corresponding single crystal, was observed in BaF2 nanophosphors.