| Luminescent materials played an irreplaceable role in the national economy and people’s daily lives because they had widely used in variety fields such as display, lighting, information storage and amplification, medical diagnosis and so on. Hexa-aluminate is the most important matrix as luminescent materials. Some rare earth and transition metal ions doped hexa-aluminate had high luminescence intensity under UV and VUV excitation and stability, non-toxicity, free pollution in the process of preparation and application. Therefore, the development and research on hexa-aluminate phosphors have an important significance.Tb3+ and Eu2+ are main rare earth ions. The transition type of two ions is different. The emission of Tb3+ is fâ†'f forbidden transition and sharp line spectra, which is hardly affected by outer crystal field. While the emission of Eu2+ is broadband spectra and dâ†'f allowable transition, which is susceptive to crystal field.Tb3+ and Eu2+ doped BaAl12O19 phosphors were synthesized by sol-gel method. The effects of preparation method, technological conditions, matrix change and co-actived ions on crystal structure and luminescence properties of phosphors were investigated systematically by X-ray diffraction, scanning electron microscopy, excitation and emission spectra.BaAl12O19:Tb and BaAl12O19:Eu phosphors were prepared by sol-gel method using citric acid as complexing agent. The effects of pH value, crystallization temperature, crystallization time and activated ions concentration on the structure and luminescence properties of phosphors were studied.The obtained BaAl12O19:Tb phosphors had a hexagonal structure and Tb3+ ions substitute Ba2+ ions into BaAl12O19 phase. The excitation peak of BaAl12O19:Tb was a wide band at around 250 nm, originated from the 4fâ†'5d transition of Tb3+. The emission spectrum of BaAl12O19:Tb consisted of a series of narrow-band emission peaks at 489nm,543nm,587nm and 623nm, originating from 5D4â†'7FJ(J=6,5,4,3) transitions of Tb3+, respectively. The emission intensity of BaAl12O19:Tb phosphors was strongest when the phosphors were crystallized at 1300℃for 2h, and Tb3+ ion concentration was 0.02 mol.BaAl12O19:Eu phosphors had a hexagonal BaAl12O19 crystal structure with space group P63/mmc. The excitation spectrum of BaAl12O19:Eu showed a broad excitation band at 323 nm, originating from fâ†'d transition of Eu2+. Under 323nm excitation, BaAl12O19:Eu phosphors showed an asymmetric and broad emission band. According to Gaussian fit analysis, this asymmetric emission was composed of three peaks, locating at 438 nm,462nm and 511 nm, respectively. The emission intensity of BaAl12O19:Eu phosphors was strongest at 446 nm when the phosphors were crystallized at 1350℃for 2h, Eu2+ ion concentration was 0.1 mol and nAl3+/n(Ba2++ Eu2+)=10:1.Sr2+, K+, La3+, Zn2+, B3+ and Li+ ions were doped into BaAl12O19 matrix to improve luminescence properties of BaAl12O19:Tb and BaAl12O19:Eu phosphors. The shape and position of emission peaks of BaAl12O19:Tb were not changed by introduction ions, but the emission intensity of phosphors were affected. The doping of Sr2+, K+, Zn2+, B3+ions improved the luminescence intensity, and the role of four ions in improvement of emission intensity for BaAl12O19:Tb from strong to weak was as follows: B3+> Zn2+> K+> Sr2+The addition of Li+ ion was unfavorable to the emission of BaAl12O19:Tb phosphors.For BaAl12O19:Eu phosphor, the intensity, shape and position of emission peaks were affected by ions doping. The emission peaks intensity was improved by the doping of Sr2+, Zn2+, Li+ ions. Of these, the half-width of emission peaks were decreased by Sr2+ and Zn2+ doping, resulting emission peaks blue-shift; While the addition of Li+ also decreased the half-width of emission peaks, but emission peak moved to long-wave area. The role of three ions in improvement of emission intensity for BaAl12O19:Eu from strong to weak was as follows: Li+>Sr2+>Zn2+The doping of B3+ and La3+ ions decreased the emission intensity of BaAl12O19:Eu phosphors. Mn2+doped BaAl12O19:Tb and BaAl12O19:Eu phosphors were prepared and their luminescence properties were investigated. The results showed that emission energy of Mn2+ originated partly from Tb3+ and Eu2+, and the emission of Tb3+ and Eu2+ ions were decreased by Mn2+ ions. In Ce3+ and Tb3+ co-doped BaAl12O19 phosphors, Ce3+ was a high efficient sensitization agent of Tb3+, Ce3+transferred its absorbed energy to Tb3+ and increased emission intensity of Tb3+. In comparison with Tb3+, the addition of Ce3+ didn’t effectively increase the emission of Eu2+ because of the competition of energy absorption between Ce3+ and Eu2+.BaAl12O19:Eu phosphors were prepared by using ultrasound-sol-gel, combustion-sol-gel. Compared with sol-gel method, the comlexing method played a role in improving the luminescence properties of BaAl12O19:Eu.The innovation of this paper:1) New green-emitting BaAl12O19:Tb phosphors were prepared. The maximum absorption peak of BaAl12O19:Tb was 250nm, which had a strong absorption for ultraviolet radiation at 254 nm. So this phosphor could become a promising green phosphor. In Ba1-xAl12O19:Tbx phosphors, Tb3+ ions substituted for Ba2+ions into BaAl12O19 phase in the ion range x=0.005～0.05.2) Through the comparison of luminescence properties of phosphors with different activators in same matrix, the effect of structure stability and charge balance on luminescence properties of phosphors were investigated, which provide reference for improving luminescence properties of currently existing phosphors and developing new luminescence materials.3) Energy transfer of Tb3+ to Mn2+ in BaAl12O19 was firstly studied, which broaden the option range of sensitizer and provide a theoretical basis for synthesis of high-efficiency luminescence materials.4) Two kinds of comlexing method were put forward to further optimize the preparation process, which find a new thought for phosphors preparation. |
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