Stability of upconversion luminescence from Tm3+, Yb3+ doped yttrium fluoride, oxyfluoride and oxide phosphors under continuous 980 nm laser irradiation

Potential applications for upconversion phosphors, like spectral shifting for solar cell enhancement and emissive 2D and 3D volumetric displays, require stability under continuous infrared irradiation. While degradation studies for cathodoluminescence (electron beam) and white light emitting diodes (ultraviolet or blue light) are widespread, little information has been published on the effect of long-term high-power irradiation on upconversion phosphors. Introductory studies on yttrium fluoride and yttrium oxide, as well as intermediate oxyfluorides, are presented. Ytterbium and thulium co-doping produced ultraviolet, blue, red and infrared upconversion emissions. The intensities were monitored under continuous 980 nm excitation, while scanning electron microscopy and X-ray photoelectron spectroscopy were used to compare irradiated and reference samples. While the intermediate oxyfluoride phases exhibited higher emission intensities, they were also most susceptible to degradation. The ultraviolet emission band of all the phosphors was most sensitive to degradation and the phosphor with yttrium oxide host was generally most resilient.