Cationic pair substitution in LaAlO3:Mn4+ for octahedral-tilting-dependent zero-phonon line

Zero-phonon line (ZPL) emission of Mn4+, without the participation of phonons, is tightly related to the host crystal structure. However, the intensity of the intrinsic ZPL is much weaker than that of Stokes and anti-Stokes vibrational bands, and it always leads to a discontinuous emission peak. Regulating the ZPL of Mn4+ for a strong emission is very important but remains a challenge for perovskite-type oxides. Here, novel La1-xBaxAl1-xTixO3:0.001Mn(4+) (LBAT:0.001Mn(4+), x = 0-0.2) and La1-yYyAl1-yGayO3:0.001Mn(4+) (LYAG:0.001Mn(4+), y = 0-0.2) samples were successfully synthesized through a high-temperature solid-state reaction, and a tunable ZPL of Mn4+ was found by cationic pair substitution of Ba2+-Ti4+ and Y3+-Ga3+ for La3+-Al3+ in LaAlO3:Mn4+. The ZPL intensity is related to the local symmetry around Mn4+ and the ZPL energy corresponds to the Mn-O bond distance and the O-Mn-O bond distortion. Through co-doping Ba2+-Ti4+, the ZPL at 710 nm is enhanced and the intensity increases continuously with increasing the x value, due to the local symmetric degree of Mn4+ decreasing slowly. However, Y3+-Ga3+ co-doping induces a linear and quick increase in the intensity of ZPL at 704 nm with increasing y value, due to the local symmetric degree of Mn4+ decreasing quickly. The octahedral tilting distortion is very important for the local symmetry. Ba2+-Ti4+ co-doping reduces octahedral tilting distortion, but Y3+-Ga3+ co-doping induces a serious octahedral tilting distortion. Consequently, the ZPL emission exhibits an octahedral-tilting dependent behavior. Mainly due to the larger distortion of the O-Mn-O bond, the energy of ZPL for LYAG:0.001Mn(4+) is higher than that for LBAT:0.001Mn(4+). The outcomes of this work provide a promising way to regulate the ZPL intensity and energy by tuning the local structure around Mn4+, and may have wide implications for Mn4+-doped phosphors and solid-state lighting.