Luminescent-Efficiency Improvement by Alkaline-Earth Fluorides Partially Replacing MgO in 3.5MgO center dot 0.5MgF(2)center dot GeO2:Mn4+ Deep-Red Phosphors for Light Emitting Diodes

We have investigated the luminescent properties of 3.5MgO center dot 0.5MgF(2)center dot GeO2:Mn4+ partially replaced by alkaline-earth fluorides under near-UV and blue light excitations. The alkaline-earth fluoride other than MgF2 probably acts as a flux. The sample with the replacement of 0.8 mol of MgO by 0.8 mol of SrF2, i.e., 2.7MgO center dot 0.5MgF(2)center dot 0.8SrF(2)center dot GeO2:0.02Mn(4+) (MGF-SF08), shows efficient deep-red emission at 659 nm, and its photoluminescence (PL) intensity is over 3 times higher than a commercial (Y,Gd)(3)(Al,Ga)(5)O-12:Ce3+ (YAG) phosphor, P46-Y3, under 450 nm light excitation. Under 405 nm light excitation, MGF-SF08 is over 7 times higher than a commercial Y2O2S:Eu3+ (YOS) phosphor, P22-RE3, in PL peak intensity. Moreover, the alkaline-earth fluorogermanate phosphors show more thermal stability than the YAG and the YOS phosphors in integrated PL intensity. The integrated PL intensity of MGF-SF08 at 150 degrees C is still 95% of that measured at room temperature under 405 nm light excitation. These results imply that Mn4+-doped alkaline-earth fluorogermanates are promising candidates of deep-red phosphors for near-UV and blue light emitting diodes.