First principles calculations of structure, vacancy defects, thermodynamic and mechanical properties and near-infrared luminescence properties of Li2CaGeO4 and Er3+: Li2CaGeO4 crystals

Abstract

Li2CaGeO4 and Er3+: Li2CaGeO4 crystals were successfully grown by TSSG method. The electronic structure, vacancy defects, near-infrared luminescence, thermodynamic stability, and mechanical properties of the crystals were characterized and analyzed by first principles calculation and experimental tests. The results show that Li2CaGeO4 and Er3+: Li2CaGeO4 crystals are typical wide-gap direct bandgap crystals (3.64 and 3.96 eV). The effect of two cationic vacancy defects on crystal properties was studied. The results show that the defects of O2− or Li+ vacancy leads to the change of band structure, and the coupling degree between conduction band and valence band is reduced, and the degree of hybridization is reduced. The probability of non-radiative transition increases greatly and the luminescence intensity decreases. Spectral tests show that the Er3+: Li2CaGeO4 crystal is an excellent laser crystal with a high near-infrared optical output at 1550 nm (4I13/2 → 4I15/2) and long fluorescence decay lifetime (5.804 ms). The thermal vibration and elastic constants of Er3+: Li2CaGeO4 crystal are calculated by simulation. The results show that Er3+: Li2CaGeO4 crystal is a kind of crystal material with easy processing, good brittleness, good thermal stability, and excellent thermal conductivity. Therefore, it has a very high application prospect in the field of laser or thermoelectric.