Matrix Effect on Fluorescent Properties of Mn²⁺ in Oxide Compounds for Red-emitting Phosphor

Abstract

Red fluorescent properties of Mn²⁺ in oxide compounds were investigated in order to improve the chromaticity of red emitting-phosphors. Mg₄Ta₂O₉ and Mg₄Nb₂O₉ with corundum-type structure were selected for the matrix of Mn²⁺ based on the ionic radius and oxygen coordination number of Mn²⁺ site. Mg₄Ta₂O₉ : Mn²⁺ with excitation of 254 nm shows a red fluorescence centered at 660 nm due to the ⁴T₁→⁶A₁ transition of Mn²⁺. On the other hand, Mn ions in Mg₄Nb₂O₉ do not show any fluorescence. The measured CIE chromaticity value of the red fluorescence of Mg₄Ta₂O₉ : Mn²⁺ is x = 0.713, y = 0.287; therefore the chromaticity of red fluorescence of Mg₄Ta₂O₉ : Mn²⁺ is better than that of commercially available Y₂O₃ : Eu³⁺ with x = 0.630, y = 0.365. However, the red fluorescence intensity of Mg₄Ta₂O₉ : Mn²⁺ is about one-third that of Y₂O₃ : Eu³⁺. The compositional dependence of fluorescent properties of Mn ions in Mg₄Ta₂O₉ and Mg₄Nb₂O₉ with corundum-type structure was discussed in terms of stability of crystal structure. The relationship between the preparation conditions and the red fluorescence intensity of Mg₄Ta₂O₉ : Mn²⁺ was also discussed based on the redox of Mn ions.