Confocal and time-resolved photoluminescence spectra of MgAl₂O₄ spinel crystals irradiated with swift heavy bismuth ions

Laser confocal microscopy technique (60 ps laser pulse excitation at 445 nm) and a time-correlated single photon counting (TCSPC) technique have been used to study photoluminescence (PL) in 710 MeV Bi ion irradiated MgAl2O4 single crystals. It was shown that radiation defects produced by swift Bi ions give rise to luminescence with peak at 1.9 eV. Gaussian deconvolution of the PL spectrum reveals that the band consists of three components: the first with a peak at 1.8 eV, the second at 2.1 eV, and the third at 2.35 eV. For the spinel sample irradiated to a fluence of Φ = 1×10¹² ions/cm², both PL and time-resolved photoluminescence (TRPL) spectra were measured as a function of depth within the irradiated layer using a confocal geometry. It was found that with increasing energy loss due to elastic collisions, the PL peak undergoes a redshift, which is more pronounced compared to surface emission measurements.