Influence of Eu3+ on the Structure and Photophysical Properties in (Y,Gd)F3 Nanophosphors

First Principle Surface Analysis of YF3 and Isostructural HoF3

The trifluorides of the two high field strength elements yttrium and holmium are studied by periodic density functional theory. As a lanthanide, holmium also belongs to the group of rare earth elements (REE). Due to their equivalent geochemical behavior, both elements form a geochemical twin pair and consequently, yttrium is generally associated with the REE as REE+Y. Interestingly, it has been found that DFT/DFT+U describe bulk HoF₃ best, when the 4f-electrons are excluded from the valence region. An extensive surface stability analysis of YF₃ (PBE) and HoF₃ (PBE+Ud/3 eV/4f-in-core) using two-dimensional surface models (slabs) is performed. All seven low-lying Miller indices surfaces are considered with all possible stoichiometric or substoichiometric terminations with a maximal fluorine-deficit of two. This leads to a scope of 24 terminations per compound. The resulting Wulff plots consists of seven surfaces with 5-26% abundance for YF₃ and six surfaces with 6-34% for HoF₃. The stoichiometric (010) surface is dominating in both compounds. However, subtle differences have been found between these two geochemical twins.

Structural, optical spectroscopy and energy transfer features of Tb3+-activated (Y, Gd)F3 nanophosphors for UV-based LEDs

A 15-fold intense green emission at 545 nm is observed in a Tb3+-activated (Y, Gd)F3 nanophosphor with high Tb3+ content and minimal Gd3+ concentration.