The effects of structural characterization on the luminescence of Eu3+-doped fluoride nano/microcrystals

Abstract

The pure tetragonal crystal phase LaOF:Eu³⁺ (2 mol%) nanocrystals (NCs) are obtained by annealing ultrasmall-sized LaF₃:Eu³⁺ (2 mol%) NCs assisted with the surfactant oleic acid. Spectroscopic characterization of Eu³⁺ in various host materials, including hexagonal-phase LaF₃, NaYF₄ and NaLaF₄, cube-phase NaYF₄, tetragonal-phase LiYF₄ and LaOF crystals, is performed to tune the luminescence by controlling the host matrices with different compositions or different phase structures of the same inorganic compound. The excitation and emission spectra arising from LaOF:Eu³⁺ (2 mol%) clearly show that the excitation and emission profiles are different from those of the other matrices. By combining the equation of the spectral conversion with the emission and excitation spectra, it is evident that the efficiency of the spectral conversion in the LaOF host material is superior to that in others, indicating a potential application in solar cells. The underlying reason for the enhanced efficiency of the spectral conversion in the LaOF host material is explored, and a mechanism based on the low local symmetry induced by the shortened bond distance and the asymmetric spatial distribution of the chemical bonds of anions coordinating the rare-earth ions is proposed.