On the Mn4+ R-line emission intensity and its tunability in solids

• Published in: Optical materials Vol. 91; no. C; pp. 338 - 343
• Main Authors: Brik, M.G., Beers, W.W., Cohen, W., Payne, S.A., Cherepy, N.J., Piasecki, M., Srivastava, A.M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01-05-2019; Elsevier
• Subjects: Luminescence; MATERIALS SCIENCE; Mn4; R-line; Red phosphors; White LED; Mn4; Red phosphors; R-line; Luminescence; White LED
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2019.03.046

The spectroscopic properties of Mn4+ ions in solids are analyzed to establish key parameters that are responsible for the energy and the intensity of the 2Eg→4A2g zero-phonon emission transition (R-line). These two factors of the emission spectrum are critical in determining the phosphor luminosity or brightness. The emission energy is chiefly determined by the “Mn4+-ligand” bonding covalence. In fluorides, the Mn-F bonding covalence is weak, and the R-line occur at higher energy. In oxides, the stronger Mn-O bonding covalence reduces the energy of the 2Eg state. In oxides, the R-line shifts to higher energy with increasing local distortion of the MnO6 octahedral moiety. Those host crystals that locate the Mn4+ ion at a noncentrosymmetric site (absence of inversion symmetry) relax the parity section rule, which enhances the R-line intensity. Increased R-line intensity in the emission spectrum produces color changes that increases phosphor luminosity. The influence of second coordination sphere (next-nearest neighbors) on the R-line intensity is considered. This article establishes guidelines for the development of host crystals that meet the requirements of high luminosity phosphors for general illumination applications.
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•Key parameters responsible for the energy and the intensity of the 2Eg.→4A2g zero-phonon emission transition of Mn4+ are established.•The energy of this transition is determined by the Mn4+-ligand covalency.•The intensity of this transition is determined by the local symsmetry of the Mn4+ position (absence of the inversion center).