Optical and electronic properties of undoped La_2Be_2O_5 single crystals in the far ultraviolet energy range

Abstract

The optical and electronic properties of undoped La2Be2O5 single crystals were determined using low-temperature (T=10  K) far ultraviolet (4.9–33 eV) synchrotron radiation spectroscopy, optical absorption spectroscopy (T=80 and 320 K), and calculations for the dispersions of the optical functions. On the basis of the obtained data we determined the Urbach’s formula parameters and the cut-off energy Ec=5.49  eV at 80 K for the low-energy tail of the host absorption, the bandgap Eg=6.78  eV at 10 K, the energy threshold for the creation of unrelaxed excitons Eex=6.28  eV, and other electronic properties.