| Rare earth phosphors have become a representative product during the fourth generation of lighting revolution and have great prospect. Silicates are considered as ideal host materials for rare earth phosphors owing to their excellent properties, such as stable chemical and thermal properties, abundant raw materials, easy and adaptable synthesis methods and high luminous efficiency. In this study, luminescent powders of Bi4Si3O12:Sm3+,M(M=La3+,Ti4+,Eu3+,Dy3+) and Bi4Si3O12:Sm3+were synthesized by a Sol-gel method with raw materials of Bi(NO3)3·5H2O, HNO3, ethanol, Sm2O3, TEOS and citric acid and so on. In order to get the best preparation process, the quantities of citric acid and nitric acid, the optimal concentration of rare ions were ascertained. The particle-size distribution of the samples, luminescence properties, micro-structure and phase were characterized by laser granularity analyzer, spectroscopic analysis, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM), concluded as follow:(1) The optimal mole ratio of citric acid and Bi(NO3)3·5H2O was X=1. The results of XRD analysis showed that better crystallinity and high purity of Bi4Si3O12:Sm3+ phosphors could be obtained at 800 ℃ for 4h. The SEM analysis showed that irregular shape of particle attached to the surface of the sol-gel synthesis red phosphor samples, the particle diameter range of 0.5-1μm.(2) Bi4Si3O12:Sm3+had a broad excitation band from 300nm to 500nm in the fluorescence spectrum, corresponding to the transition,6H5/2→4F7/2,6H5/2→4H9/2, 6H5/2→4D3/2,6H5/2→4D7/2,6H5/2→4I13/2 of the Sm3+ ions. The main emission peaks locate at 566nm,609nm and 655nm and the emission bands extend from 500-750nm. The emission spectra was described by the well-known 4Gs/2→6HJ (J=5/2,7/2,9/2) emission lines of the Sm3+ ions. The optimal condition concentration of Sm3+ ions was 4mol%. The chromaticity coordinates of sample was (0.52,0.47) which the color coordinates were located in the orange red region.(3) The strongest excitation peaks of Bi4Si3O12:Dy3+ phosphor located at 450nm and 467nm. The emission peaks at 480nm and 579nm corresponding to blue and yellow regions and the sample emits bright white light under the excitation of 347nm.The best optimized doping concentration of Dy3+ is 3mol%, concentration quenching phenomenon occurs when the concentration exceeds 3mol%.(4) The main excitation peak of Bi4Si3O12:Eu3+ phosphors locates at 261nm, attributed to the charge migration zone of Eu3+ and O2- and the sample has strong emission peaks at 595nm and 614nm.The optimized doping concentration of Eu3+ is 4mol% and the chromaticity coordinates of sample was (0.62,0.37). This indicates Bi4Si3O12:Eu3+ has a superior performance and is a potentially useful red phosphor.(5) Amount of metal Ti4+ ion doping has impact on the luminescent properties of Bi4Si3O12:Sm3+ phosphors. When λex=404nm or 466nm, the main emission peak locates at 607nm, moved toward shorter wavelength by 2nm, resulting in blue shift. The doping of Ti4+ ions can significantly enhance the emission intensity of the sample, corresponding to different excitation wavelengths, Ti4+ optimum doping concentration is different. When λex=404nm, optimized doping concentration of Ti4 +is 25mol%; when using 466nm near blue light to excite the sample, the sample optimized doping concentration is 20mol%.(6) In the Sm3+, La3+ co-doped Bi4Si3O12 phosphors, there is energy transfer between Sm3+ and La3+ ions. La3+ ions can absorb part of the excitation energy and transmit it to the Sm3+, which enhances the radiative transitions of 4G5/2→>6HJ of Sm3+, thereby Sm3+ ions emitting sensitized.(7) In the excitation spetra of Bi4Si3O12:Eu3+, Sm3+ phosphors, with the increasing content of Eu3+, the emission intensity of Sm3+ increased and there are Eu3+ characteristic emission peaks in the emission spectrum. It suggests that Eu3+ is not only the luminescent center but also can sensitize the luminescence of Sm3+ and enhance fluorescence emission intensity. When the amount of substance ratio of nEu3+/nSm3+ equals 1, the emission intensity of the sample reaches best and the luminous color coordinates of the sample moves to red region.(8) The excitation spetra of Bi4Si3O12:Dy3+, Sm3+ shows that the Dy3+ ions as a sensitizer, it can transfer energy to Sm3+, so that the electrons transition of Sm3+ is more likely to occur on the transition level, which can significantly enhanced fluorescence emission. When the optimized doping concentration of nDy3+/nSm3+equals 0.75, the luminous brightness was increased significantly and the sensitizing effect reaches the best point. |
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