Intrinsic luminescence in yttrium trifluoride

Luminescence and excitation spectra as well as their temperature dependence were investigated for nominally pure yttrium trifluoride powders using synchrotron radiation. Broad emission bands in VUV-visible spectral range were observed under excitation above 11 eV in YF₃ at 10 K. At least three emission bands were distinguished peaking at 5.6 eV (220 nm), 4.5 eV (280 nm) and 3.1 eV (400 nm). It was shown that the emission bands at 5.6 eV (220) and 4.5 eV (280 nm) are intrinsic but the long wavelength emission at 3.1 eV (400 nm) is of extrinsic nature. The excitation spectra for the two intrinsic luminescence bands have their individual features, but in both cases a sharp peak at the fundamental absorption edge is observed. This fact as well as a large Stokes shift of intrinsic luminescence (more than 5 eV) and a large width of the emission bands (near 1 eV) allows us to assign the 4.5 eV (280 nm) and 5.6 eV (220 nm) emission to the radiative decay of self-trapped excitons in YF₃. The strong influence of temperature on the intrinsic luminescence, observed at temperatures above 120 K, are used to evaluate the activation energy of thermal quenching.