Rare‐earth fluorides are a class of materials with considerable potential in optical applications. Fluoride lattices typically permit high coordination numbers for the hosted rare‐earth ions, and the high ionicity of the rare‐earth‐to‐fluorine bond leads to a wide bandgap and very low vibrational energies. These factors make rare‐earth fluorides very useful in optical applications employing vacuum ultraviolet and near‐infrared excitation. The preparation of nanometer‐sized particles has opened the door for new properties and devices if the performance of their macroscopic counterparts can be conserved in the nanometer regime. However, at small particle sizes, defect surface states and adhering water reduce the optical efficiency. These shortcomings can be reduced by applying protective shells around the luminescent cores, which can also be involved in the luminescent process.

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 µm) 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.

Rare earth fluorides are a class of materials with a high potential for optical applications. Fluoride lattices allow high coordination numbers for the hosted rare earth ions, but the high ionicity of the rare earth to fluorine bond leads to a wide band gap and very low vibrational energies. These two essential factors, in particular, contribute to their practicality for use in optical applications based on vacuum ultraviolet (VUV) and near infrared (NIR) excitation. The preparation and optical characteristics of rare earth fluoride nanoparticles and their embedding in polymeric, glassy or porous matrices are very promising for the eventual manufacture of transparent hybrid materials. Recent attempts to control the size of these particles down to the nano-scale and, at the same time, maintaining the performance of their macroscopic counterparts, indicate accessibility of hitherto unrealized optical properties and applications.

No abstract