Luminescence of nanocrystalline BaFCl codoped with Eu and Tb.

BaFCl:Eu,Tb nanocrystals were synthesized hot-injection thermolysis of metal chlorodifluoroacetates and their luminescence response characterized between 80 and 430 K. Though unintended, partial reduction of Eu to Eu occurred during the synthesis stage, leading to luminescent nanocrystals coactivated by Eu, Eu, and Tb. Their emission was dominated by Eu, specifically by radiative transitions 4f (P) → 4f (S) and 4f5d (lowest level) → 4f (S). Owing to the thermal coupling between 4f (P) and 4f5d (lowest) levels, line-like emission from this manifold at 80 K evolved into band-like emission at 430 K. The change in the shape of the emission profile of Eu was used to demonstrate that BaFCl:Eu,Tb may serve to realize bandshape luminescence thermometry as a more straightforward alternative to the usual ratiometric approach. The energy gap between 4f (P) and 4f5d (lowest) levels and their radiative transition probabilities were estimated from time-resolved variable-temperature decays.