Comment on “Charge Transfer-Triggered Bi ³⁺ Near-Infrared Emission in Y ₂Ti ₂O ₇ for Dual-Mode Temperature Sensing”

Abstract

Undoped Y ₂Ti ₂O ₇ exhibits impurity emission bands at low temperatures due to Mn ⁴⁺ and Cr ³⁺, as established by codoping with these ions. Contrary to a recent report by Wang et al., ACS Appl. Mater. Interfaces 2022, 14, 36834–36844, we do not observe Bi ³⁺ emission in this codoped host, as also is the case for Fe ³⁺. The emission reported in that paper as being due to Bi ³⁺ in fact corresponds to Cr ³⁺ emission. The Cr ³⁺ and Mn ⁴⁺ emissions are quenched with increasing temperature, so that Mn ⁴⁺ emission is scarcely observed above 80 K. We present variable temperature optical data for Y ₂Ti ₂O ₇ and this host codoped with Mn, Cr, Fe, and Bi, as well as a theoretical justification of our results.