Cao Renping,Ceng Dong,Liu Pan,Yu Xiaoguang,Guo Siling,Zheng Guotai
LaAlO 3 :Mn 4+ and LaAlO 3 :Mn 4+ , Na + deep red-emitting phosphors are synthesized by a solid-state reaction method in air. Their crystal structures, lifetimes, and luminescence properties are investigated, respectively. PLE spectrum monitored at 730 nm contains three PLE bands peaking at ~276, 325, and 500 nm within the range 200–550 nm, and PL spectrum with excitation 325 nm exhibits two PL band peaks located at ~703 and 730 nm owing to anti-stokes vibronic sidebands associated with the excited state 2 E of Mn 4+ ion and the 2 E → 4 A 2 transition of Mn 4+ ion, respectively. The optimal Mn 4+ doping concentration is ~0.8 mol%. Lifetime of LaAl 0.992 O 3 :0.8 %Mn 4+ phosphor is ~0.92 ms. Na + ion as charge compensator can improve obviously the luminescence properties of LaAlO 3 :Mn 4+ phosphor due to the charge compensation. The luminous mechanism of Mn 4+ ion is explained by using Tanabe–Sugano diagram of Mn 4+ ion in octahedral crystal field. The contents of this paper will be helpful to develop novel Mn 4+ -doped materials and improve their luminescence properties.
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−xTixO3:0.001Mn4+ (LBAT:0.001Mn4+, x = 0–0.2) and La1−yYyAl1−yGayO3:0.001Mn4+ (LYAG:0.001Mn4+, 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:0.001Mn4+ is higher than that for LBAT:0.001Mn4+. 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.
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