VUV spectroscopy of BaF 2:Er

Abstract

Luminescence and luminescence excitation spectra of BaF 2:Er in UV and VUV have been measured at Superlumi station in Hamburg, in search for fast and efficient VUV scintillator materials. Although, under selective VUV excitations, we observe the 4f 105d–4f 11 VUV emission, it is relatively slow and is not efficiently excited at VUV wavelengths below 124 nm. The structure observed in the VUV excitation spectra reflects rearrangement of ten 4f electrons left behind by transition promoting one of the 4f electrons of the original 4f 11 configuration to the lowest energy d-orbital. Other emission bands, excited at complementary VUV wavelengths, are due to the 4f 11 intra-configuration transitions. The VUV excitation mechanism of these transitions involves a bound exciton at Er 3+ ion. Subsequent large energy relaxation leading to the F–H pair associated with the Er 3+ ion prevents energy transfer to the higher lying states of the 5d4f 10 configuration. Even when the 5d4f 10 configuration is reached directly, the coupling between the 5d and 4f 10 electrons generating the high and low spin (HS and LS) excited states of the 5d4f 10 configuration is responsible for relatively slow d–f emission in BaF 2:Er. In summary, the Er 3+ activated BaF 2 fails to provide fast and efficient emission under ionizing excitation, expected of new scintillating materials.