Morphology Controlling And Spectral Regulation Of Rare Earth Doped Phosphate And Silicate Phosphors

After the incandescent lamp, fluorescent lamp, and high-pressure sodium lamp, phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as the fourth generation light source due to their unique properties including energy savings, environment-friendliness, small volume, long persistence and high energy efficiency. Currently, the approach to obtain the white light is solely based on the combination of a blue LED (GaN) and a yellow-emitting phosphor (YAG:Ce). However, it exhibits poor color rendering index, high correlated color temperature, and color reabsorption due to the deficiency of red emission. Accordingly, WLEDs fabricated with near ultraviolet LED chips and single matrix white light phosphors can effectively overcome the defects of commercial LED. Therefore, development of high physical and chemical properties, high luminous efficiency of the single matrix multicolor emission fluorescence materials has become one of the hotspots in the field of white LED. On the other hand, the phosphor properties of grain size, microstructure, and dispersion also get the attention of the industry. It has become another research hot. So, in this work, we reported the rare earth or transition metal doped new phosphate KSrY(PO4)2 (KSYP) and new silicate Sr3Y2(Si3O9)2 (SYSO) which can be excited by near-ultraviolet light via solid state reaction method or hydrothermal synthesis method. In the meantime, the samples were analyzed and characterized by XRD, FT-IR, SEM, TEM, SAED, grain size analysis, XPS, UV-vis, PL, fluorescence lifetime, QYs, Fullprof and GSAS refinement software and we systematically studied the powder crystal structure, grain size, ions placeholder, microstructure, fluorescence properties, energy transfer and so on. The main contents are listed as follows:1. A series of single-phased emission KSYP:Ce3+, Tb3+, KSYP:Ce3+, Mn2+ phosphors were synthesized by solid-state reaction. The PL spectrum of KSYP:Ce3+, Tb3+ gives a broad band of Ce3+ and a series of peaks of Tb3+ which are located at 485,541,583 and 621 nm. The PLE and reflectance spectra demonstrate that KSYP:Ce3+, Tb3+ has two strong and broad absorption bands with maxima at 275 and 320 nm appear in the 250-350 nm region, which are assigned to the f → d absorption of the Ce3+ ions. The energy transfer from Ce3+ to Tb3+ in the KSYP host has been demonstrated to be the exchange interactions, and the energy transfer efficiency can be reached at 68%. The PL spectrum and decay curves are demonstrated that the energy transfer from the Ce3+ to Mn2+ ions is dominated by the electric dipole- dipole interaction. By controlling the doping content of the Mn2+ ions with a fixed Ce3+ content, the emission color of the phosphor varied from blue region to orange region;2. A novel single-composition white-emitting phosphor KSrY(PO4)2:Ce3+, Tb3+, Mn2+ has been synthesized by a high-temperature solid-state reaction. The results of XRD indicate that the obtained phosphors are single phase and the co-doped Ce3+, Tb3+, Mn2+ ions do not cause any significant change. The PL spectra of KSYP:Ce3+, Tb3+, Mn2+ are found to consist of six emission bands in the visible-wavelength region, one at 401 nm (Ce3+5d1→4f1 transition), four green-emitting Tb3+ peaks located at about 481,543,581 and 622 nm, and a broad orange-emitting band at 570 nm (due to a Mn2+ d-level spin-forbidden transition). The energy transfers from Ce3+ to Tb3+ and Ce3+ to Mn2+ in KSYP host matrix are demonstrated. A single composition white-light emitting phosphor KSYP:0.01Ce3+,0.01Tb3+) 0.06Mn2+, which shows correlated color temperature of 5110 K, color rendering index of 46, and color coordinates of (0.341,0.337), was obtained by controlling the doping content of the Ce3+, Tb3+, Mn2+;3. A series of KSYP:Eu were synthesized by hydrothermal synthesis method. When the additive was polyethylene glycol (PEG) and the precursor was alkaline, FT-IR, XRD and structure refinement results demonstrated the synthesis of pure phosphate KSYP phases. The XPS and fluorescence spectra results indicated when the additive is PEG, it obtained the Eu3+ doping KSYP orange phosphor. The KSYP:Eu3+samples were the hollow tube structure at different pH value. There was not significant influence on the morphology of samples when changed the molecular weight of PEG. However, it could improve the dispersivity of the samples, and increase the intensity of emission. When the additive was citric acid (CA) and the precursor was weak acid, neutral or alkaline, it could obtain the pure KSYP phase. The XPS and fluorescence spectra results indicated the Eu2+ doping KSYP blue phosphor. It could control the sample particles from 400-800 nm spindles to 50 nm spherical particles and enhanced the intensity of emission when changed the pH value;4. A series of SYSO:Ce3+, SYSO:Eu2+phosphors were synthesized by the solid-state reaction. The PL spectrum of SYSO:0.05Ce3+ shows an asymmetric emission band. The red shift emission and the occupation of Ce3" in the SYSO host could be discussed by crystal field theory and Uitert’s empirical formula. Under 340 nm UV excitation, SYSO:Eu2+ shows a broad band extending from 400 to 620 nm which is assigned to the 4f65d1→4f7 transition of Eu2+.5. The Ce3+→Tb3+ energy transfer in SYSO green phosphors has been demonstrated to be the dipole-quadruple mechanism. In the SYSO:Ce3+, Tb3+ phosphors, the critical distance (RC) of energy transfer was calculated to be about 13.2 A, the maximum efficiency of energy transfer was 78.4%, and the quantum yields (Qys) could reach above 90.4%. In the SYSO:0.15Ce3+, yMn2+ phosphors, The maximum energy transfer efficiency of this system was calculated to be 50.5%. By controlling the doping content of the Mn2+ ions, the emission color of the phosphor varied from blue region (0.159,0.038) to white region (0.302,0.336), and eventually to yellow region (0.337,0.396). In the SYSO host, there is also the energy transfer process of Ce3+ →Eu2+. The chromaticity coordinates of Ce3+ and Eu2+ co-activated SYSO phosphors locate in cyan area covering the blue and green regions. What’s more, the cyan emission intensity of Ce3+ and Eu2+ co-doped SYSO samples are clearly higher and broader than those of Eu2+ single doped samples. It is helpful to improve the color rendering index of the samples.