| As a new generation of lighting source, white light emitting diodes (LED) have variety applications in the field of lighting, display, anti-forgery, bio-medicine and sterilization. Inorganic luminescence materials play a major part in the industry of white LED, for they would influence the luminescence efficiency and color rendering index of the device. At present, there are two main ways to achieve white light:one is the combination of the blue chip with Y3Al5Oi2:Ce3+ (YAG:Ce3+), the other is the combination of the ultraviolet (UV) chip with red/green/blue tri-color phosphors. However, neither one is perfect. For the former, the obtained white light shows high color temperature and low color rendering index for lacking red light component, makes it hard to satisfy day light requirement. And the latter faces the problem of re-absorption between different phosphors and low energy transfer efficiency. This essay focuses on the current issue of the existing inorganic luminescence materials, the researches have been carried out in three aspects:1. We synthesize two kinds of red-emitting phosphor RbZnPO4:Eu3+ and YBa3(PO4):Eu3+ via high temperature sintering and discuss their structure and luminescence properties. The structure of Eu3+ doped RbZnPO4 and the crystal field around Eu3+are analyzed in detail based on the XRD refinement data. The emission spectrum shows a main peak at 698 nm, which is ascribed to the 5Doâ†'7F4 transition of Eu3+. The temperature quenching spectrum indicates the emitting of RbZnPO4:Eu3+is sensitive to temperature. And we discuss the temperature dependent luminescence property with Arrhenius model, charge compensation mechanism and CASTEP band structure analysis. While for Eu3+doped YBa3(PO4)3 phosphor, they show bright red light emission peaked at 612 nm upon 393 nm excitation, which is due to the 5Doâ†'7F2 transition of Eu3+. The integrate intensity is 3.13 times of that of commercial Y2O3:Eu3+ phosphor, with a superior CIE coordinates of (0.654,0.338). Besides, the rare earth free red-emitting Mn2GeO4 phosphor is synthesized via hydrothermal method. The crystal and band structure are discussed with XRD refinement and CASTEP band structure analysis. The SEM results show regular hexagram-shaped morphology with average diameters of about 38.8 μm. The luminescence properties are discussed with excitation, emission and temperature quenching spectra.2. Single Ce3+ doped Sr5(PO4)2SiO4 white light emitting phosphor and Dy3+doped RbZnPO4 white/yellow light emitting phosphor are synthesized via high temperature sintering. Ce3+can occupy two kinds of Sr sites in Srs(PO4)2SiO4, giving blue light (nine-coordinated 4f sites) in the spectral range of 375-500 nm and yellow emitting (seven-coordinated 6h sites) at about 500-675 nm. The white light can be achieved both by the variation of excitation and the adjustment of Ce3+ contents. Upon 365 nm excitation, Srs(PO4)2SiO4:0.05Ce3+ shows CIE color coordinates of (0.33, 0.34), a superior color-rendering index of 90 and correlated color temperature of 5603 K, suitable for 365 nm UV-GaN chip. Besides, the photoluminescence properties can be enhanced by co-doping charge compensation agents. These results demonstrate that mono Ce3+ activated Sr5(PO4)2SiO4 has the potential to serve as novel phosphors to be applied in W-LEDs. As for RbZnPO4:Dy3+, the excitation spectrum shows strong absorption in the ultraviolet and blue region, suitable for ultraviolet and blue LED chip excitation. Upon 386 nm excitation, the emission spectrum shows several peaks at 487,577 and 672 nm, which should be ascribed to the 4F9/2â†'6HJ (J=15/2,13/2 and 11/2) transition of Dy3+. The CIE coordinates are calculated to be (0.44,0.47), with color temperature of 3374 K, indicating that it shows warm white emission. When excited at 455 nm, RbZnPO4:Dy3+shows similar emission spectra with that of upon 386 nm excitation and it also exhibits good thermal stability. The simulated combination of the blue LED chip with RbZnPO4:Dy3+ phosphor in CIE 1931 chromaticity shows that warm white light emission with color temperature of 3125 K and CIE of (0.42,0.39) can be obtained.3. We synthesize CaAl2O4:Eu2+, Nd3+ nanofibers by means of electrospinning, followed by a subsequent annealing process for the first time. The SEM,TEM, XRD, EDX, element mapping studies show the intermediate state is composed of hollow CaAl2O4:Eu2+, Nd3+@carbon, in which the outer sheath can be easily removed. The optical spectrum shows CaAl2O4:Eu2+,Nd3+exhibits a broad band emission centered at 445 nm. After carefully discussing the afterglow and trap situation, we hope to get alternating current used LED material to solve the present stroboscopic problem. |
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