Effect of vacuum annealing on the upconversion luminescence of β-Ba2ScAlO5: Yb3+, Ho3+ phosphor

Upconversion luminescence (UCL) materials with narrow emission peaks, long fluorescence lifetime, and large anti-Stokes shift have attracted considerable attention in biomedical, display, anti-counterfeiting, and solid-state lasers. This study presents a new synthesis method, combining air sintering and vacuum annealing, to obtain intense green UCL emission β-Ba2ScAlO5: 0.15 Yb3+, 0.005Ho3+ phosphor. After vacuum annealing, the green, red, and near-infrared emissions of Ho3+ are enhanced by factors of 40, 133, and 37, respectively. The diffuse reflectance spectra demonstrate that there is a defect energy band ranging from 330 to 860 nm in the air-treated samples, and it is reduced dramatically after vacuum annealing. This defect band covers the three wavelengths of Ho3+ emissions in the visible range and results in the reabsorption of UCL by the host lattice. X-ray Rietveld refinements and EPR spectra reveal the difference in the oxygen defects of the air-synthesized and vacuum-annealed phosphors and reflect that the absorption band is related to the oxygen defects. This research provides a new approach to obtain intense UCL emission of β-Ba2ScAlO5 hosted phosphors and offers an excellent green phosphor for application in anti-counterfeiting or displays.