Luminescent-Efficiency Improvement by Alkaline-Earth Fluorides Partially Replacing MgO in 3.5MgO⋅0.5MgF[sub 2]⋅GeO[sub 2]:Mn[sup 4+] Deep-Red Phosphors for Light Emitting Diodes

Abstract

We have investigated the luminescent properties of 3.5MgO·0.5MgF 2 ·GeO 2 :Mn 4+ partially replaced by alkaline-earth fluorides under near-UV and blue light excitations. The alkaline-earth fluoride other than MgF 2 probably acts as a flux. The sample with the replacement of 0.8 mol of MgO by 0.8 mol of SrF 2 , i.e., 2.7MgO·0.5MgF 2 ·0.8SrF 2 ·GeO 2 :0.02Mn 4+ ͑MGF-SF08͒, shows efficient deep-red emission at 659 nm, and its photoluminescence ͑PL͒ intensity is over 3 times higher than a commercial ͑Y,Gd͒ 3 ͑Al,Ga͒ 5 O 12 :Ce 3+ ͑YAG͒ phosphor, P46-Y3, under 450 nm light excitation. Under 405 nm light excitation, MGF-SF08 is over 7 times higher than a commercial Y 2 O 2 S:Eu 3+ ͑YOS͒ 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°C is still 95% of that measured at room temperature under 405 nm light excitation. These results imply that Mn 4+ -doped alkaline-earth fluorogermanates are promising candidates of deep-red phosphors for near-UV and blue light emitting diodes.