Tm 3+ -mediated energy bridge in lead-free double perovskites: suppressing multiphonon relaxation for multifunctional photonic applications

The Tm 3+ – 3 H 5 level bridges Er 3+ : 4 I 11/2 and 4 I 13/2 states, suppressing multi-phonon relaxation, and enhancing the red/green emission radio 50-fold versus Er 3+ -single-doped GMTO.