Site Occupation and Luminescence of Novel Orange-Red Ca₃M₂Ge₃O₁₂:Mn²⁺,Mn⁴⁺ (M = Al, Ga) Phosphors

Abstract

Novel orange-red-emitting phosphors Ca3M2Ge3O12:Mn2+,Mn4+ (M = Al, Ga) with sufficient red light component were developed, and their lattice occupancy and luminescent properties of different color centers have been studied. In Ca3M2Ge3O12:Mn, the abnormal self-reduction of Mn4+ to Mn2+ occurs. The doped manganese ion (using MnO2 as Mn source) occupies dodecahedron Ca2+ site forming Mn2+(I) color center with orange emission, while it occupies octahedral Al3+/Ga3+ site forming Mn2+(II) and Mn4+ color centers with red and deep red light emission. The thermal quenching properties show that Ca3M2Ge3O12:Mn (M = Al, Ga) samples have low thermal quenching, and the thermal quenching of Mn2+(I) is lower than that of Mn2+(II) due to existence of more defects nearby the Mn2+(II) providing additional nonradiative recombination decay path. Ca3Al2Ge3O12:Mn has a lower thermal quenching than Ca3Ga2Ge3O12:Mn because the former possesses higher rigidity. The obtained results reveal that Ca3M2Ge3O12:Mn2+,Mn4+ (M = Al, Ga) has potential practical value in WLEDs. Moreover, the luminescence of Mn2+ and Mn4+ ions in a matrix provides a new strategy for designing and synthesizing new luminescent materials.