| The laser materials doped with Nd3+ ions have become the hotspot because Nd3+ ion has large absorption coefficient, wide absorption band, long fluorescence lifetime, very large fluorescence branching ratio, energy compaction and the possibility of lasing at different wavelengths at room temperature. Transparent oxyfluoride glass ceramics doped with Nd3+ ions have attracted widespread interest due to their excellent optical properties like fluoride nanocrystals and good mechanical, chemical properties like oxide glasses. Compared with other fluoride, CaF2 has high solid solubility to rare earth, wide transmission range (0.125-10um),good chemical stability, and lower phonon energy, so the transparent oxyfluoride glass-ceramics containing CaF2 doped with Nd3+ become one kind of very potential laser materials.In this thesis, the transparent oxyfluoride glass-ceramics of SiO2-Al2O3-CaF2-NaF-Na2O system doped with Nd3+ ions were prepared by conventional melt-quenching method and optimized heat treating regime. The glass-forming ability, crystallization mechanism, microstructure of SiO2-Al2O3-CaF2-NaF-Na2O system glasses were analyzed by differential thermal analyse (DSC), X-ray diffraction (XRD) analysis and scanning electronic microscopy (SEM). The absorption spectra and fluorescent spectra of the glass-ceramics samples were measured. The influences of Nd3+ content on the spectrum properties of glass-ceramics were discussed. The results show that the glasses of SiO2-Al2O3-CaF2-NaF-CaO have good glass-forming ability. Surface crystallization and the crystals of anorthite appeared at the higher temperatures. When CaO is replaced by Na2O, the crystallization ability of the glass is improved. The crystals of CaF2 is obviously detected at the temperature of the crystallization first peak, and the Nd3+ ions incorporate into CaF2 nano-crystals and Ca0.9Nd0.1F2.1 solid solution formed. Obviously, a large amount of network disconnected points or non-bridge oxygen ions exist in the network structure formed by connecting [SiO4] and [SiO4] or [SiO4] and [AlO4] since the molar percentage of NaF and CaF2 are higher than 25% in SiO2- Al2O3- CaF2- NaF-Na2O system glass. Therefore, the crystallization activation energy declines gradually with Nd2O3 content, resulting in the increasing of crystallization ability in this glass system. During the crystallization, the crystalline grains grow along three-dimension directions when the basic glasses are treated at the crystallization temperature, and the crystallization is controlled by diffusion. The increasing of the crystallization leads to the reduce of nucleation rate, ultimately to zero. With the increasing of Nd3+ content, solid solution Ca0.9Nd0.1F2.1 appear besides CaF2 crystals in different Nd3+ containing samples after the same heat treatment, and Ca2+ ions are replaced by Nd3+ ions which make the diffraction peak move to smaller angle. The more Nd3+ ions incorporate into CaF2, the more serious of the crystal lattice distortion, so diffraction peak shift more. Accordingly, with the amount of Nd3+ ions increase, the number of crystals increases after heat treatment. This further approves that Nd3+ ions are good for the crystallization of CaF2. The crystallization of Ca0.9Nd0.1F2.1 and the increase of crystal lattice distortion approve Nd3+ ions incorporate into CaF2 nano-crystals. Because the phonon energy of CaF2 crystal is less than the one glass matrix, the absorption optical density and emission intensity of Nd3+ ions are enhanced. The various charge compensation mechanisms and asymmetric crystal lattices of CaF2 result in a broaden absorption spectra and fluorescent spectra. In SiO2- Al2O3- CaF2-NaF-Na2O glass system, there are five main absorption peaks of Nd3+ at 511,582,746,803 and 875nm, and three main fluorescent peak of Nd3+ at 888,1055 and 1327 nm corresponding to the transition of 4F3/2â†'4I9/2, 4F3/2â†'4I11/2å'Œ4F3/2â†'4I13/2, respectively with the concentration of Nd3+ ions increase, CaF2 crystals form square anti-prism sites of cubo-octahedral cluster, causing the concentration quenching effect, resulting in stimulated emission cross-section of the glass ceramics decreases. |
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