Emission properties and temperature quenching mechanisms of rare-earth elements doped in garnet hosts

Abstract

Thermographic phosphors continue to be investigated for gas thermometry in combustion applications due to their relative non-intrusiveness and ability to survive harsh environments. To further develop this technology, the mechanisms leading to their temperature-sensitive emission must be understood in greater detail. As a result, this work focuses on the quenching mechanisms of four different thermographic phosphors: Pr:YAG, Pr:LuAG, Ce:YAG, and Ce:LuAG. Spectrally- and temporally-resolved emission measurements were performed in a tube furnace, providing data on the emission properties of the phosphors at elevated temperatures. A quantum mechanical single configurational coordinate (QMSCC) model is used to understand the temperature sensitivity of the emission spectrum and of the nonradiative intersystem crossing. Energy diagrams for each phosphor are constructed to understand the likelihood of nonradiative ionization to the conduction band as a thermal-quenching mechanism. Configurational coordinate diagrams for each phosphor are constructed and used to interpret the mechanism responsible for thermal quenching. It is found that intersystem crossing is responsible for thermal quenching of Pr:YAG and Pr:LuAG, whereas ionization to the conduction band is the likely mechanism for Ce:YAG and Ce:LuAG. The ability to understand and model the mechanisms associated with the temperature-sensitive emission properties will be a valuable tool towards choosing appropriate thermographic phosphors for specific gas thermometry applications.