Comparative Upconversion of Tm, Yb‐Doped YF ₃ , YOF, and Y ₂ O ₃ Hosts

Upconverting phosphors have applications in security printing, forensics, biomedical research, and temperature sensing. Achieving efficient upconversion luminescence requires suitable host materials. Fluorides are generally favored for their low phonon energy, but the oxide Y 2 O 3 is also used commercially. During annealing in air, YF 3 can transform into Y 2 O 3 via intermediate oxyfluoride phases. This study aimed to determine which host material results in the strongest blue upconversion emission from Tm 3+ ions after excitation of the Yb 3+ ions with an infrared diode laser at 980 nm. YF 3 doped with 0.5 mol% Tm 3+ and 10 mol% Yb 3+ was prepared by coprecipitation and annealed at different temperatures up to 1500°C to produce the phases studied, which were characterized by X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy, and diffuse reflectance. Upconversion luminescence bands for the various hosts were investigated through excitation power dependence studies. The lifetime of the blue upconversion luminescence (476 nm) was measured. The mixed phase powder annealed at 950°C was used to demonstrate forensic fingerprint detection with blue upconversion light, since it exhibited the strongest emission. This study demonstrates that intermediate oxyfluoride materials have potential as upconversion hosts that may be superior to the corresponding fluorides and oxides.