Pure and Pr³⁺-doped BaYF₅ nanoparticles were synthesized by the microwave hydrothermal method. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and optical spectroscopy. The XRD and TEM confirm that the average size of nanoparticles is in the range of 26-37 nm. The optical excitation and luminescence spectra of BaYF₅:Pr³⁺ nanoparticles are presented in the visible and ultraviolet (UV) range. It has been verified that Pr³⁺ ions are capable of emitting UV-C photons when excited by a 444 nm laser. This emission arises from a two-photon energy-transfer upconversion mechanism. The concentration dependence of the upconversion luminescence of BaYF₅:Pr³⁺ was studied.

The recent COVID-19 pandemic has made everyone aware of the threat of viruses and the growing number of antibiotic-resistant bacteria. It has become necessary to find new methods to combat these hazards. One tool that could be used is UVC radiation, i.e., 100–280 nm. Currently, the available sources of this light are mercury vapor lamps. However, the modern world requires more compact, mercury-free, and less energy-consuming light sources. This work presents the results of our research on a new material in which efficient UVC radiation was obtained. Here, we present the results of research on Ca₉Y(PO₄)₇ polycrystals doped with Pr³⁺ ions prepared using the solid-state method. The absorption, excitation, emission, and emission decay profiles of praseodymium(III) ions were measured and analyzed. The upconversion emission in the UVC region excited by blue light was observed. Parameters such as energy bandgap, refractive index, and thermal stability of luminescence were determined. The studied phosphate-based phosphor possesses promising characteristics that show its potential in luminescent applications in future use in medicine or for surface disinfection.

Herein, the structure, morphology, as well as optical properties of the powder and ceramic samples of Ba₂MgWO₆ are presented. Powder samples were obtained by high temperature solid-state reaction, while, for the ceramics, the SPS technique under 50-MPa pressure was applied. The morphology of the investigated samples showed some agglomeration and grains with a submicron size of 490–492 µm. The theoretical density and relative density of ceramics were calculated using the Archimedes method. The influence of sample preparation on the position, shape, and character of the host, as well as dopants emission was investigated. Sample sintering enhances regular emission of WO₆ groups causing a blue shift of Ba₂MgWO₆ emission. Nonetheless, under X-ray excitation, only the green emission of inversion WO₆ group was detected. For the ceramic doped with Eu³⁺ ions, the emission of both host and dopant was detected. However, for the powder efficient host to activator energy, the transfer process occurred, and only the magnetic dipole emission of Eu³⁺ was detected. The intensity of Nd³⁺ ions of Ba₂MgWO₆ powder sample is five times higher than for the ceramic. The sintering process reduces inversion defects and creates a highly symmetrical site of neodymium ions. The emission of Ba₂MgWO₆:Nd³⁺ consists of transitions from the ⁴F_3/2 excited level to the ⁴I_J multiplet states with the dominance of the ⁴F_3/2→⁴I_11/2 one. The spectroscopic quality parameter and branching ratio of Nd³⁺ emission are presented.

The spectroscopic properties of Pr³⁺ ions in the aluminosilicate matrix were investigated for the first time. Synthesis of CaAl₂SiO₆ (CASO) polycrystals doped with Pr³⁺ ions was carried out using the sol–gel method. The crystalline structures have been confirmed with XRD measurement. The absorption, excitation, emission spectra, and time decay profiles of the praseodymium (III) ions were measured and analyzed. It was found that upon excitation with visible light, this material exhibits emission mainly in the UVC region, via an upconversion emission process. The Stokes emission in the visible range is observed mainly from the ³P₀ and ¹D₂ energy levels. The ¹D₂→³H₄ emission is very stable even at very high temperatures. The studied aluminosilicate phosphors possess characteristics that confirm their potential in upconversion emission applications.