Synthesis and characterization of luminescent Ln3+ (Ln = Eu, Tb and Dy)-doped LiYF4 microcrystals produced by a facile microwave-assisted hydrothermal method

This paper reports microstructural and luminescent properties of lithium yttrium fluoride (LiYF4) doped with rare earth ions. Submicrometric crystals of LiYF4 were successfully produced using the microwave-assisted hydrothermal method, which allowed the formation of single crystalline phase at temperatures as low as 140 °C for a reaction time of 15 min. The structural study was carried out by X-ray diffraction (XRD), revealing single tetragonal phase. The electronic structure and microstructure formation of LiYF4 was investigated through the binding energy of the atoms, measured via X-ray photoemission spectroscopy (XPS) and scanning electron microscopy (SEM). The luminescent properties as scintillator were investigated through X-ray excited luminescence (XEL) and time-resolved luminescence. Spectroscopy studies were done via photoluminescence (PL) technique in the visible (VIS) and vacuum ultraviolet (VUV) regions, from ∼1.0 to 15.0 eV. PL excitation results showed that the band gap (Eg) of the LiYF4 is at around 11.0 (±0.1) eV. 4f-5d transitions were identified for Eu3+, Tb3+ and Dy3+. The experimental data were used to predict the energy levels of all divalent and trivalent lanthanide (Ln) ions relative to the valence and conduction bands of LiYF4 and to construct the host referred binding energy (HRBE) and vacuum referred binding energy (VRBE) schemes.