Upconversion luminescence of nano-sized Yb and Tm codoped rare earth phosphates, that is, LaPO and YPO, has been investigated under high-pressure (HP, up to ∼25 GPa) and high-temperature (293-773 K) conditions. The pressure-dependent luminescence properties of the nanocrystals, that is, energy red shift of the band centroids, changes of the band ratios, shortening of upconversion lifetimes, and so forth, make the studied nanomaterials suitable for optical pressure sensing in nanomanometry. Furthermore, thanks to the large energy difference (∼1800 cm), the thermalized states of Tm ions are spectrally well-separated, providing high-temperature resolution, required in optical nanothermometry. The temperature of the system containing such active nanomaterials can be determined on the basis of the thermally induced changes of the Tm band ratio (F → H/H → H), observed in the emission spectra. The advantage of such upconverting optical sensors is the use of near-infrared light, which is highly penetrable for many materials. The investigated nanomanometers/nanothermometers have been successfully applied, as a proof-of-concept of a novel bimodal optical gauge, for the determination of the temperature of the heated system (473 K), which was simultaneously compressed under HP (1.5 and 5 GPa).

Anti-Stokes luminescence of up-converting nanocrystals SrF:Yb,Er can be used as a high pressure optical sensor alternative to the ruby fluorescence-scale. In nanocrystalline SrF:Yb,Er, high pressure reversibly shortens the emission lifetimes nearly linearly up to 5.29 GPa at least. Its advantage is the use of NIR (≈980 nm) radiation, highly penetrable for many materials. The shortening of up-conversion lifetimes has been attributed mainly to the changes in energy transfer rates, caused by decreased interatomic distances and increased overlap integrals between 4f electrons and the valence shells of ligand ions. The origin of high-pressure effects on the luminescence intensity, band ratio and their spectral position has been explained by the increased interactions and distortions of the crystal-field symmetry around the emitting ions in the compressed structure.

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Monoclinic Gd(1-x)Eu(x)BO(3) nanopowders were successfully synthesized using a modified Pechini method. The crystal structure of the prepared materials was revised and confirmed using several techniques such as: IR, XRD, TEM, Raman spectroscopy and EDX analysis. The obtained material was comprised of particles, consisting of parts with the average size 350 nm. The luminescence properties of the prepared phosphors with different concentrations of Eu(3+) ions were characterized by excitation and emission spectra and its kinetic decay. The Judd-Ofelt parameters (Ω(2), Ω(4)), quantum efficiency, η, and chromaticity coordinates were also calculated.

A new method was used to obtain Eu(3+)-doped LaOF nanocrystals. The obtained nanocrystals were synthesized for the first time using a modified Pechini sol-gel method. The products were analyzed by X-ray powder diffraction and the Rietveld method. Optimal conditions for the synthesis were found. Luminescent properties of the tetragonal and rhombohedral LaOF:Eu(3+) nanocrystals were investigated by collecting excitation and luminescence spectra. The most effective dopant concentrations in both hosts were found. Luminescent lifetimes were also measured. The time-resolved luminescent traces showed both a growth and a decay, which pointed to energy transfer processes between Eu(3+) ions in the LaOF host. In order to explain these phenomena, an adequate mechanism has been proposed. Intensity parameters Ω(2), Ω(4) and quantum efficiencies were calculated using the Judd-Ofelt theory, allowing for an extensive study of the luminescent properties of Eu(3+) ion in the LaOF matrix.