High temperature thermoluminescence of BaFCl:Eu²⁺ X‐ray storage phosphor

Abstract

Thermoluminescence (TL) of Eu2+ -doped BaFCl polycrystalline powders X-ray irradiated at room temperature show several TL peaks at 364 K, 408 K, 470 K, 524 K and 646 K. Thermally activated recombination processes responsible for TL have been studied using complementary techniques as TL and its bleaching, diffuse reflectance, X-ray excited luminescence (XL) and photostimulated luminescence (PSL). Experimental results indicate that F(Cl -) centres are the dominant electron trap centres, the Eu 2+ -trapped hole aggregate centres playing the role of recombination centres. The 470 K and 646 K TSL glow peaks are assigned to the recombination inside the triple aggregates (Eu 2+ -hole centre -F(Cl -) centre). The remaining 408 K and 524 K TL peaks are tentatively assigned to recombination between F centres and double aggregates (Eu 2+ -hole centre).

Facile Ionic Liquid‐Assisted Strategy for Direct Precipitation of Eu2+‐Activated Nanophosphors under Ambient Conditions

“…This emission band is distributed between 24 000 and 28 000 cm −1 , peaking at 26 380 cm −1 , with FWHM of 1756 cm −1 and assigned to the 4f 6 5d 1 →4f 7 electronic transition of Eu 2+ ions . This Eu 2+ 4f 6 5d 1 →4f 7 emission is very similar to the one in the bulk material, however the intense shoulder detected at lower energy in the emission band of bulk material and attributed to Eu 2+ luminescence perturbed by an impurity is not observed in this nanomaterial . As observed in Figure b, the excitation spectrum of 2 consists of a broad band in the UV spectral range, rising at about 27 000 cm −1 , with maximum at 36 300 cm −1 .…”

“…The room temperature decay time determination of 2 shows a double exponential behavior, which can be fitted to τ 1 = 82 ns and τ 2 = 333 ns when the detection is set at 26 370 cm −1 (380 nm) (see Figure S8 in the Supporting Information). These lifetimes are, in general, very fast for Eu 2+ based f ↔ d transitions, especially if compared to those of the bulk materials (3300 ns) . However, different arguments can explain these values, namely (i) in nanoparticles, the boundary effect improves the electron photon coupling leading to additional quenching effects, (ii) the ionic liquid attached at the surface of the nanoparticles also exhibits luminescence at 380 nm via π–π* transitions which are extremely fast and may cause energy transfer Eu 2+ ‐ILs (most probably the short lifetime τ 1 = 82 ns is attributed to this procedure), (iii) the change of refractive index between BaFCl:Eu 2+ and BmimBF 4 could also have an incidence on the life time measurements, and (iv) the higher surface to volume ratio in nanoparticles usually involves increases of the surface defects concentrations leading to shorter decay time via nonradiative relaxation processes.…”