科研之友
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摘要
In this work, the crystal field stabilization energy (D-q) and the Racah B and C parameters were calculated quantitatively to evaluate the nephelauxetic effect of Mn4+ suffering from the Sr4Al14O25 host, aiming for developing novel highly efficient red phosphor for white light-emitting diodes. The phosphor of Mn4+ activated Sr4Al14O25 was synthesized via a high temperature solid reaction in air ambient. The crystallinity was investigated using the X-ray diffraction; and the photoluminescence properties were characterized with the spectrometer. The red emission was attributed to the Mn4+ which occupies the center of AlO6 octahedron. Meanwhile, the Mn2+ and Mn3+ were detected by using the X-ray absorption near-edge structure spectroscopy (XANES) assisted with Electron Paramagnetic Resonance (EPR) techniques. The energy levels of (4)A(2), T-4(2g) and T-4(1g) were determined according to excitation spectra, corresponding to the (4)A(2) (t(2)(3)) -> T-4(-1) (F-4) and the (4)A(2) (t(2)(3)) -> T-4(2g) (t(2)(2)e) transitions at 330 and 450 nm respectively, whereby the calculation was carried out according to the Tanabe-Sugano diagram for octahedral complex with the d(3) electron configuration. The nephelauxetic ratio beta about 0.32 suggests a strong cloud expansion of Mn4+ in the Sr4Al14O25 crystal lattice with D-q similar to 2222 cm(-1), B similar to 794 cm(-1), C similar to 3232 cm(-1) and C/B similar to 4.07. In the perspective of physics, these parameters are helpful to perceive the inter-repulsion of the outer electrons in 3d orbit of Mn4+ and the effect of local circumstance, in essential to understand the variant spectral configurations of Mn4+ luminescence observed in different hosts.
