The effects of thermal processing on the luminescence of Y2O3:Tm transparent ceramic

Transparent ceramics of Y₂O₃ doped with 0.5 mol% Tm were fabricated starting from the synthesis of the precursor nanopowder by co-precipitation and calcination followed by its consolidation into fully dense ceramics. Densification and optical transparency of the ceramic were achieved by means of sequential steps of cold isostatic pressing at 206 MPa, vacuum sintering using the two-step method at 1500 °C for a brief moment and at 1400 °C for 20 hrs, and hot isostatic pressing at 1300 °C for 6 hrs under 206 MPa of argon. After polishing to optical grade, samples were thermally processed at 1050 °C in O₂ flux for a total of 10 hrs. Thermal processing was interrupted at specific times and photoluminescence and thermoluminescence were characterized. X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) measurements were also carried out and revealed the microstructural modifications induced by the thermal processing. Results reveal significant enhancement of luminescence concomitant to a strong decrease of the integral thermoluminescence intensity within the first hour of thermal processing, followed by stabilization. Traps above about 150 °C were strongly affected by the thermal treatment under O₂ flux and were assigned to oxygen-related defects. These results are discussed in terms of the incorporation of oxygen into the structure and the elimination of defects and electronic traps.