The nature of Bi3+ luminescence in garnet hosts

The room temperature photoluminescence and excitation spectra of Bi3+ in the (Y,Gd)3(Al,Ga)5O12 garnets is reported and analyzed. The luminescence spectra of these materials under 1S0 → 3P1 Bi3+ excitation consist of two bands in the UV and the visible spectral regions. The UV emission band is attributed to the 3P0,1 → 1S0 emission of isolated Bi3+ ions and is observed for the first time in garnet host lattices. Previous reports of Bi3+ luminescence in (Y,Gd)3Ga5O12 garnets only reported the visible emission and attributed this emission to an impurity trapped exciton, implying a strong interaction between the host lattice conduction band and the Bi3+ excited states. We disagree with this interpretation of the visible emission band. Our results show a strong dependence of the visible band intensity on the Bi3+ concentration and lead us to conclude that this emission is related to Bi3+ pairs and/or clusters in the garnet host lattice. There does not appear to be any interaction between the host lattice conduction band and the 3P0,1 excited states of Bi3+.