Thermal quenching of Mn4+ luminescence in Sn4+-containing garnet hosts

A series of Mn4+-doped multi-component garnet ceramics comprising Sn4+ ions at octahedral sites, namely Ca3SnScGaSi2O12, Ca2YSnMgAlSi2O12, Ca2YSnGaGa2SiO12 and Ca2YSn2Ga3O12, were synthesized and investigated as red emitting phosphors for warm white pc-LEDs. It turned out that all synthesized phosphors exhibit rather poor thermal stability of the Mn4+ luminescence which is almost completely quenched at room temperature. The low thermal quenching temperature of Mn4+ luminescence for these phosphors is related to the low energy of the Mn4+4T2 and O2− - Mn4+ charge transfer states which can serve as quenchers for Mn4+ luminescence. It is proposed that a higher thermal stability of Mn4+ luminescence can be expected for compounds in which Mn4+ ions substitute for host cations having a lower charge and/or smaller size than Mn4+.