Deep Ultraviolet Emitting Scintillators for Biomedical Applications: The Hard Way of Downsizing LuPO4:Pr3+

Pr3+-doped LuPO4 emits UV radiation between 225 and 280 nm, where DNA shows strong absorption bands. Therefore, a systematic study of the luminescence of Pr3+ doped LuPO4 is performed: Different doping concentrations, particles sizes, and excitation schemes (vacuum UV at 160 nm and X-rays 50 kV, 2 mA, tungsten target) are compared. The emission spectra in the UV range depends on the excitation energy and the particle size. Microcrystalline particles (6 mu m) comprising 1% Pr3+ display the highest emission intensity at 234 nm upon vacuum UV as well as X-ray excitation. Sub-microscale particles (20-50 nm) of LuPO4:Pr3+ (1%) show the same UV emission under X-ray excitation as the larger particles but do not emit under vacuum UV excitation. Colloidal nanoscale particles (5 nm) do not show emission in the UV-C range. Based on the high-density and strong X-ray absorption of LuPO4, the implementation of Pr3+ doped LuPO4 particles of suitable size (20-50 nm) could improve the well-established radiation therapy. Owing to the strong absorption and low penetration depth of UV-C radiation in biological tissue, Pr3+-doped LuPO4 particles located directly in cancerous tumors could allow for additional treatment with cell-damaging UV-C radiation.