Three-dimensional (3D) rapid prototyping technology based on near-infrared light-induced polymerization of photocurable compositions containing upconversion nanomaterials has been explored. For this aim, the rationally-designed core/shell upconversion nanoparticles NaYF₄:Yb³⁺,Tm³⁺/NaYF₄, with the distinct ultraviolet-emitting lines and unprecedentedly high near-infrared to ultraviolet conversion efficiency of $${\eta }_{{\bf{UC}}}^{({\bf{UV}})}=2{\boldsymbol{ \% }}$$η UC ( UV ) = 2 % have been used. The upconverted ultraviolet photons were capable to efficiently activate photoinitiators contained in light-sensitive resins under moderate intensities of NIR excitation below 10 W cm⁻² and induce generation of radicals and photopolymerization in situ. Near infrared-activated polymerization process, both at the millimeter and sub-micron scales, was investigated. Polymeric macro- and microstructures were fabricated by means of near infrared laser scanning photolithography in the volume of liquid photocurable compositions with focused laser light at 975 nm wavelength. Examination of the polymerization process in the vicinity of the nanoparticles shows strong differences in the rate of polymer shell growth on flat and edge nanoparticle sides. This phenomenon mainly defines the resolution of the demonstrated near infrared - ultraviolet 3D printing technology at the micrometer scale level.

A method for measuring refractive index n of nanosize particles in the visible and near-IR spectral ranges is proposed. The method is based on comparing refractive index n _colloid of a colloid solution of nanoparticles in several solvents with refractive indices n _solvent of corresponding pure solvents and has an accuracy of ±2 × 10⁻⁴. Upconversion nanosize phosphors (UCNPs) are synthesized in the form of a β-NaYF₄ crystalline matrix doped with Yb³⁺, Er³⁺, and Tm³⁺ rare earth ions. UCNPs have a doped core with a diameter of 40 ± 5 nm and undoped shell with a thickness of 3–5 nm. Synthesized nanocrystals possess intense photoluminescence in the blue, green, and red spectral ranges upon excitation by IR radiation with a wavelength of 977 nm. Using a spectroscopic refractometer, the dispersion of the refractive index of β-NaYF₄/Yb³⁺/Er³⁺/Tm³⁺ nanocrystals was measured for the first time in the spectral range of 450–1000 nm with an accuracy of ±2 × 10⁻⁴.

Cubic KR₃F₁₀ (R = Y, Tb) single crystals have been successfully grown using the Bridgman technique. Growth of crystals of this type is complicated due to the hygroscopicity of potassium fluoride and melt overheating. The solution to the problem of oxygen-incorporated impurities has been demonstrated through the utilization of potassium hydrofluoride as a precursor. In this study, the crystal quality, structure features, and optical, thermal and electrophysical properties of KR₃F₁₀ were examined. Data on the temperature dependences of conductivity properties of KTb₃F₁₀ crystals were obtained for the first time. These crystals indicated thermal conductivity equal to 1.54 ± 0.05 Wm⁻¹K⁻¹ at room temperature caused by strong phonon scattering in the Tb-based crystal lattice. Ionic conductivities of KY₃F₁₀ and KTb₃F₁₀ single crystals were 4.9 × 10⁻⁸ and 1.2 × 10⁻¹⁰ S/cm at 500 K, respectively, and the observed difference was determined by the activation enthalpy of F⁻ ion migration. Comparison of the physical properties of the grown KR₃F₁₀ crystals with the closest crystalline analog from the family of Na_0.5−xR_0.5+xF_2+2x (R = Tb, Y) cubic solid solutions is reported.