Ultrabroadband red luminescence of Mn4+ in MgAl2O4 peaking at 651 nm

Blue light pumped red luminescence with broadband and high photon-energy emission is highly desired for phosphor-converted white light-emitting diodes (LEDs), to achieve high color rendering index and high luminous efficacy. The Mn4+-doped red-emitting phosphors generally exhibit sharp vibrionic emissions associated with the parity and spin-forbidden 2 Eg → 4 A2g transition. In this paper, two abnormal luminescence behaviors were observed for Mn4+ in the MgAl2O4:Mn4+ spinel phosphor with a short wavelength emission peaking at 651 nm. Firstly, the Mn4+ 2 Eg → 4 A2g transition exhibits an ultrabroadband luminescence band in MgAl2O4 and the large full-width at half-maximum (FWHM) is dependent both on the calcination temperature and the partial substitution of Al3+ with Ga3+. Secondly, the thermal quenching behavior of the Mn4+ 2 Eg → 4 A2g luminescence in MgAl2O4 shows a dependence on its thermal treatment and preparation method. The Rietveld refinement and Raman results demonstrate that the variation in the FWHM of the luminescence spectra is a sum effect of structural ordering (i.e., isotropic displacement decrease of constituent atoms) and the Mg ↔ Al antisite disorder. A model for the observed varying thermal quenching of luminescence was tentatively proposed. The intrinsic thermal quenching temperature of Mn4+ luminescence in MgAl2O4 was verified to be 390~400 K using the samples prepared by the co-precipitation and molten salt methods. The present work gives a novel perspective to understand the luminescence spectra of Mn4+ 2 Eg → 4 A2g transition