Preparation And Luminescent Properties Al₆Si₂O₁₃:Cr³⁺ And Ba_1.1-yMg_yAl_11.8O₁₉:Mn⁴⁺ RED Phosphors

LED is known as the fourth lighting source and is the most promising lighting technology because of its high lighting efficiency, energy saving, environmental protection, long lifetime. The ultraviolet-visible (UV) light conversion of LED will be the main development direction in the future, so it is necessary to explore the efficient tricolour phosphors suited for UV-light, especially in preparation of red phosphors. In our study, Cr3+-doped Al6Si2O13 phosphors and Mn4+-doped Ba0.5Mg0.6Al11.88O19 red phosphors were synthesized by the solid-state method at high temperatures respectively. The effects of activators, dopants, matrix composition and sintering process on the luminescent properties of samples have been investigated. The spectral properties were characterized by means of spectrofluorimeter. The phase compositions and microstructure of phosphors at different temperatures were analyzed with XRD, TG-DTA and SEM respectively. In addition, absorption band, vibration mode of samples and valence states of activator were studied through ultraviolet and visible spectrophotometer, Raman spectroscopy and XPS. The results show that:1. The Al6Si2013:Cr3+, R (R=Li+,Na+,Sr2+) red phosphors were synthesized by the solid-state method at high temperatures. The results indicate that excitation peaks are located at 410nm and 555nm, corresponding to 4A2→4T1 and 4A2→4T2 spin allow transition. The main peak of emission spectrum is located at 695nm with a sharp line, ascribed to 2E→>4A2 transition of Cr3+ion. Using the spectral data, the lattice parameters of the Dq/B value can be calculated and is greater than 2.3, shows that Cr3+in strong crystal field. Spectral characteristics of specimens have not been changed by adding dopants of Li2O, Na2O or SrO, and the luminescence intensity can be enhanced to 1.7 times in the condition of 12mol%Na+. Al6Si2O13:Cr3+ phosphors are excited effectively by both near UV and blue light, then exhibit red emission with good performance.2. The Ba0.5Mg0.6Al11.8O19:Mn4+(BAM) red phosphors were prepared by the solid-state method at high temperatures. The results show that excitation spectrum is a wide band peaking at 345nm and 469nm, which corresponds to O2-→Mn4+ charge transfer band, the 4A2→4T1 electron transition and 4A2→4T2 electron transition of Mn4+respectively. Emission spectrum of BAM phosphor consists of a strong sharp line peak at 676nm and a shoulder band peak at 692nm, corresponding to 2E→4A2 transition of Mn4+ion and a phonon sideband transition respectively. The luminescence performance can be obtained in the condition with 0.5wt% Mn4+ ions and 17wt% B2O3 flux. Ba0.5Mg0.6Al11.8O19:Mn4+ phosphors are excited effectively by both near UV and blue light, then exhibit red emission with good performance.