Spectral Properties and Thermal Quenching of Mn-=SUP=-4+-=/SUP=- Luminescence in Silicate Garnet Hosts CaY-=SUB=-2-=/SUB=-MgMAlSi-=SUB=-2-=/SUB=-O-=SUB=-12-=/SUB=- (M=Al, Ga, Sc) -=SUP=-*-=/SUP=-

Multi-component silicate garnet ceramics CaY_2MgMAlSi_2O_12 comprising different cations M = Al, Ga or Sc in octahedral sites doped with Mn^4+ ions have been synthesized and studied as novel red-emitting phosphors aiming at warm white pc -LED applications. All synthesized phosphors exhibit Mn^4+ luminescence in rather deep red region, the shortest-wavelength spectrum of Mn^4+ luminescence (peak wavelength at 668 nm) being obtained for the host with the largest cation M^3+ = Sc^3+ in the octahedral site. The effect of increasing the energy of the emitting Mn^4+^2 E level with the size of the host cation in octahedral sites is supposed to be the result of decrease of the covalence of the “Mn^4+-ligand” bonding with increase of the interionic Mn^4+–O^2– distance. All studied phosphors demonstrate rather poor thermal stability of Mn^4+ photoluminescence with a thermal quenching temperature T _1/2 below 200 K, the lowest value being observed for the host with M = Sc. As expected, the decrease of the energy of the O^2––Mn^4+ charge-transfer state is observed with the increase of the M^3+ cation radius, i.e. with the increase of the O^2––Mn^4+ interionic distance. The thermal quenching temperature of Mn^4+ luminescence in the studied phosphors correlates with the energy of the O^2––Mn^4+ charge transfer state which is supposed to serve as a quenching state for Mn^4+ luminescence.