T. S. Bulatova’s research while affiliated with St Petersburg University and other places

Microcrystalline upconversion materials NaY0.8- x Yb0.2Ho x F4 ( x = 0-0.1) were synthesized by hydrothermal synthesis for the first time. All the synthesized compounds have hexagonal β-NaYF4 crystalline phase. Holmium(III) ions isomorphically replace yttrium ions. The maximum upconversion emission intensity is observed for NaY0.78Yb0.2Ho0.02F4 in the visible region of the spectrum upon excitation at a wavelength of 973 nm.

Методом гидротермального синтеза впервые синтезированы нанокристаллические люминофоры состава NaGd 1- x Nd x F 4 ( x = 0-1). Полученные соединения кристаллизуются в гексагональной сингонии, структурный тип - β-NaYF 4 . Ионы неодима(III) изоморфно замещают ионы гадолиния. Максимальная интенсивность люминесценции в ближней ИК области при возбуждении на длине волны 808 нм соответствует соединению состава NaGd 0.96 Nd 0.04 F 4 . При увеличении содержания ионов неодима происходит концентрационное тушение.

The series of luminescent NaYF4:Sm3+ nano- and microcrystalline materials co-doped by La3+, Gd3+, and Lu3+ ions were synthesized by hydrothermal method using rare earth chlorides as the precursors and citric acid as a stabilizing agent. The phase composition of synthesized compounds was studied by PXRD. All synthesized materials except ones with high La3+ content (where LaF3 is formed) have a β-NaYF4 crystalline phase. SEM images demonstrate that all particles have shape of hexagonal prisms. The type and content of doping REE significantly effect on the particle size. Upon 400 nm excitation, phosphors exhibit distinct emission peaks in visible part of the spectrum attributed to 4G5/2→6HJ transitions (J = 5/2–11/2) of Sm3+ ion. Increasing the samarium (III) content results in concentration quenching by dipole–dipole interactions, the optimum Sm3+concentration is found to be of 2%. Co-doping by non-luminescent La3+, Gd3+ and Lu3+ ions leads to an increase in emission intensity. This effect was explained from the Sm3+ local symmetry point of view.

Two series of β-NaYF4:Ln3+ nanoparticles (Ln = La–Nd, Sm–Lu) containing 20 at. % and 40 at. % of Ln3+ with well-defined morphology and size were synthesized via a facile citric-acid-assisted hydrothermal method using rare-earth chlorides as the precursors. The materials were composed from the particles that have a shape of uniform hexagonal prisms with an approximate size of 80–1100 nm. The mean diameter of NaYF4:Ln3+ crystals non-monotonically depended on the lanthanide atomic number and the minimum size was observed for Gd3+-doped materials. At the same time, the unit cell parameters decreased from La to Lu according to XRD data analysis. The diameter-to-length ratio increased from La to Lu in both studied series. The effect of the doping lanthanide(III) ion nature on particle size and shape was explained in terms of crystal growth dynamics. This study reports the correlation between the nanoparticle morphologies and the type and content of doping lanthanide ions. The obtained results shed light on the understanding of intrinsic factors’ effect on structural features of the nanocrystalline materials.