| The design and fabrication of phosphors used for white LED were paid more attention with the extension of application field and the development of elaboration technology of white LED. Recently, Sr2SiO4:Eu2+ phosphors have attracted considerable interest owing to their exceptional features such as stable physical and chemical properties, wide adjustable range of emission spectra, good optical transmission. In addition, the studies about rare earth ions doped transparent oxyfluoride glass for white LED have aroused scientists' interest, because it posses some obvious advantages, such as homogeneous light-emitting, better thermal stability, lower production cost and epoxy resin free in assembly process.In this thesis, the main contents are listed as follows:1. Sr2SiO4:Eu2+ phosphors were prepared by a conventional solid-state reaction method at a relative low temperature (1100℃) by using NH4F as a flux. The effect of NH4F flux and Eu2+ doping concentrations on the structural and luminescent properties of Sr2SiO4:Eu2+ was investigated in detail. The structural properties were studied by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The blue-shift of emission peaks with different Eu2+ concentrations were observed and analyzed. NH4F flux increased the content of monoclinicβ-Sr2SiO4 phase, enhanced the luminescent performance of Sr2SiO4:Eu2+ phosphor significantly, and NH4F flux is more superior to NH4Cl and Li2CO3 flux. Our investigation indicates that Sr2SiO4:Eu2+ is a good light-conversion phosphor candidate for near-ultraviolet chip and NH4F is a good flux forβ-Sr2Si04:Eu2+.2. Transparent Ag and Eu3+ co-doped oxyfluoride glasses with composition 50SiO2-20Al2O3-30CaF2 were prepared by melt-quenching technique. The structural and luminescent properties of glasses, energy transfer mechanism between luminescent centers were systematically investigated. The missing nanoparticles signals in absorption spectra, XRD patterns and transmission electron microscopy (TEM) images, the additional broad excitation band at 325-375 nm indicate that the broad emission band at 400-700nm is originated from very small molecule-like, non-plasmonic Ag particles (ML-Ag-particles). A perfect white light emission was realized by combining intense red emission of Eu3+ with broad band emission of ML-Ag-particles. These results suggest that Ag and Eu3+ co-doped oxyfluoride glasses could be potentially applied as white light-emitting phosphors for ultra-violet LED chips.3. Transparent glass-ceramics containing SrF2 nanocrystals were fabricated by melt-quenching and subsequent heating of glass with composition of 50SiO2-10Al2O3-20ZnF2-20SrF2. XRD, TEM, and energy dispersive spectroscopy (EDS) were used to investigated the microstructure of the SrF2 glass-ceramics. Results show that SrF2 nanocrystals were homogeneously precipitated among the aluminosilicate glass matrix, and the mean size of the SrF2 nanocrystals was about 20 nm, and Eu3+ ions partition mainly into the precipitated SrF2 nanocrystals after crystallization. The glass-ceramics exhibited intense red emission corresponding to the 5D0â†'7FJ (J=0-4) transitions of Eu3+ ions under 393 nm excitation. A significant Eu3+ luminescence enhancement by a factor of about nine times was observed after crystallization. Besides, the obvious stark splitting emissions, the low forced electric dipole 5D0â†'7F2 transition, and the long decay lifetimes of Eu3+ ions also revealed the partition of Eu3+ ions into low phonon energy SrF2 nanocrystals. Our results indicate the SrF2 based fluorosilicate glass-ceramics is an excellent host for trivalent lanthanide ions doping and may find applications in photonics. |
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