Photoluminescence and cathodoluminescence of BaAl2O4:Eu2+ and undoped BaAl2O4: evidence for F-centres

Abstract

© Copyright 2020 The Author(s). In this article the photoluminescence (PL) and cathodoluminescence (CL) of undoped BaAl2O4 and BaAl2O4 doped with 500 ppm and 3 mol% Eu2+ is described. The most important results from the CL measurements are: (1) Undoped BaAl2O4 manifested intrinsic CL at 460 nm, which increased at low temperature and did not change significantly upon exposure to the e-beam; (2) Doping BaAl2O4 with Eu2+ changed the character of the intrinsic luminescence band: it became more sensitive to temperature variations and the band experienced a blue shift to ∼425 nm; (3) electron beam (e-beam) exposure of Ba0.97Eu0.03Al2O4 at low temperature increased the 425 nm band strongly while the Eu2+ emission at ∼500 nm decreased by about 70%. The Eu2+ emission band was symmetric, indicating that BaAl2O4:Eu has changed to the P6322 phase upon e-beam exposure at low temperature; (4) We have identified the 460 nm band in undoped BaAl2O4 and the 425 nm band in BaAl2O4:Eu2+ with F-centre luminescence, corresponding to the F-centre emission in α-Al2O3. The evidence for the assignment of the 425 nm band in BaAl2O4:Eu2+ is the spectacular increase of the spectral radiance at 425 nm by e-beam exposure at 200 keV and low temperature. A preliminary model is presented that explains the results. The PL from BaAl2O4:Eu2+ quenched at the rather low temperature of 140°C; this observation is explained in terms of thermal ionization of the Eu2+ ion.