Characteristics of rare earth (RE = Eu, Tb, Tm)-doped Y ₂O ₃ phosphors for thermometry

The temperature-dependent photoluminescences of Y ₂O ₃:Eu (6% Eu), Y ₂O ₃:Tb (4% Tb) and Y ₂O ₃:Tm (1% Tm) were investigated for high-temperature phosphor thermometry. Two different phases, the monoclinic phase and cubic phase, were considered because the fluorescence spectra vary with the phase. To employ the intensity ratio method, we investigated their photoluminescence spectra under the excitation light of an Hg-Xe lamp as the temperature was elevated from room temperature to more than 1200 K. As a result, it was confirmed that the luminescence intensity of all of the phosphors varied with elevating temperature, i.e. thermal quenching, with the variations depending on the type of rare earth impurity and their phases. The results indicate that Y ₂O ₃:Eu phosphors are applicable to the intensity ratio method because they show appropriate variations in the intensity ratio of two emission lines, and they also have strong and sharp peak intensities without excessive optical noise or black body radiation over a wide range of temperatures. The intensity ratios for Y ₂O ₃:Tb provide such small variations with temperature that the temperature resolution is low, despite the strong emission intensities. As for Y ₂O ₃:Tm, the intensity ratios also have a low temperature resolution and their emission intensities are weak. Therefore, Y ₂O ₃:Tb and Y ₂O ₃:Tm are not appropriate for the intensity ratio method for phosphor thermometry.