Characterization of the Emission Properties of Thermographic Phosphors for Use in High Temperature Sensing Applications

Emission properties of fifteen different powder and crystalline thermographic phosphors have been characterized for potential use in high temperature sensing applications. Excitation and emission spectra of these rare-earth activated thermographic phosphors have been measured as a function of temperature using a special mini oven built inside of a fluorescence spectrophotometer. Several of the thermophosphors underwent decay lifetime analysis and were calibrated for use in high temperature measurements.

The excitation spectra taken from room temperature to approximately 400°C, reveal that the phosphors Y₂O₃:Eu³⁺, YV0₄:Eu³⁺, Ba₃(P0₄)₂:Eu²⁺, LaP0₄:Eu³⁺, LuP0₄: Eu³⁺, YP0₄:Eu³⁺, YV0₄:Dy³⁺, Y₂0₂S:Eu³⁺, and Y₂0₂S:Tb³⁺ exhibit a significant temperature-dependent shift in their charge-transfer (C-T) absorption band. In addition, the peak position of the charge-transfer band in the europium-doped orthophosphate crystals is located at higher energies or deeper into the ultraviolet as the cation radius of the host crystal lattice decreases. The experimental results also show that the onset quenching temperature of the orthophosphate phosphors increases as a function of decreasing cation radius. The orthophosphate crystals YP0₄:Eu³⁺, LuP0₄:Eu³⁺, and LuP0₄:Dy³⁺ were found to have high onset quenching temperatures when compared to those of the powder phosphors. Orthophosphate single-crystals may prove to be the phosphor of choice for high temperature measurements ranging from 700°C to 1400°C.