Luminescence of Bi3+ and Bi2+ ions in novel Bi-doped SrAl4O7 phosphor

Abstract

Bismuth-doped SrAl4O7 powders were synthesized via modified Pechini process and their photoluminescence, radioluminescence and thermoluminescence properties were studied and discussed. Obtained results showed that in studied materials bismuth is present in two valence states, Bi3+ and Bi2+. Upon UV excitation SrAl4O7:Bi powders yield broad multicomponent luminescence in the 350–670 nm range, associated with the 3P0,1 → 1S0 transition of Bi3+ ions, and the most intense component located in green (λmax = 515 nm) part of spectrum. It was found that the emission spectral distribution is excitation wavelength-dependent. By changing the excitation wavelength in the 270–340 nm range the emission colour can be modulated from blue, through bluish-cyan to green. The studied phosphors also showed broad-band 2P3/2 → 2P1/2 Bi2+ emission in deep red region centered at around 710 nm. This luminescence was found predominant in radioluminescence and thermoluminescence spectra, which is deemed unique for bismuth-doped materials. The Bi2+ 630–830 nm emission might be attractive for bioimaging as it appears in the Ist biological window and may be utilized for deep red scintillation.