Review—Negative Thermal Quenching of Mn4+ Luminescence in Fluoride Phosphors: Effects of the 4A2g → 4T2g Excitation Transitions and Normal Thermal Quenching

Abstract

Thermal stability of the phosphor materials is of crucial importance and scientific interest. It is well known that various Mn4+-activated phosphors, especially Mn4+-activated fluoride and oxyfluoride phosphors, show an anomalous thermal quenching behavior, i.e., an increase in the integrated photoluminescence intensity I PL with increasing temperature T, known as the negative thermal quenching (TQ) behavior. The negative TQ has been understood to be due to the electric dipole (parity) forbidden transitions of 2 E g → 4 A 2g gained by coupling with the odd-parity lattice vibrations, ν 3, ν 4, and ν 6. This article discusses the effects of the 4 A 2g → 4 T 2g excitation transitions on a negative TQ phenomenon. Our previous study suggested that the 4 A 2g → 4 T 2g excitation transitions in Mn4+-activated fluoride phosphors are strongly connected with the certain mode phonons, namely the gerade-mode ν 2 phonons, with an energy of ∼65 meV. Here, our analysis model considers this effect and is found to show good agreement with the experimental data. Discussion is also given of the temperature dependence of decay time τ(T) and quantum efficiency η(T), in comparison with I PL(T), demonstrating a strong correlation among such important phosphor properties except for an occurrence of negative TQ only in I PL(T).