Facile fabrication of Eu3+-doped lanthanum oxyfluoride powders by combustion processes and temperature analysis of its fluorescence for thermal sensor application

Lanthanum oxyfluoride powders (LaOF) doped with Eu3+ were successfully synthesized using combustion synthesis technique. Through this facile fabrication method, the most effective dopant concentration was found. Luminescent properties of LaOF:Eu3+ powders were investigated by collecting the fluorescence spectral and temporal profiles. The samples illuminated with ultraviolet (λ = 256 nm) and blue (λ = 465 nm) radiation showed the characteristic red fluorescence corresponding to 4f intraband 5D0 → 7FJ transitions of Eu3+. The fluorescence quantum efficiencies were estimated from the experimental data using Judd-Ofelt theory. The fluorescence quenching with temperature was investigated in the sample with the highest fluorescence quantum efficiency. Our results indicate that this phosphor has potential application in optical thermometry. It is assumed that this phenomenon occurs due to thermal activation of nonradiative energy transfer between europium 5D2 state and charge transfer states (CTS) of the host. The energy bandgap and the energy transfer rate between 5D2 and CTS were estimated by analyzing the dynamics of the fluorescence of transition 5D0 → 7F2 as a function of temperature. The activation energy for thermal quenching of the fluorescence was found to be the 5D2 → CTS energy bandgap.