Size effects and radiation resistance of BaF2 nanophosphors

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 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 V_H-centers with delocalization temperature of ∼140 K are the main hole centers that occur in BaF₂ nanoparticles under X-ray irradiation influence, while in F₂ single crystals – these are V_k - and H-centers with delocalization temperatures at 113 and 198 , respectively. Significant long-wave displacement of emission bands associated with (V_H-F)- and (H-F)- recombinations, compared to the spectra of corresponding single crystal, was observed in BaF₂ nanophosphors.