In this study, monodispersed and high-quality hexagonal phase LaF3 nanocrystals with different shapes and sizes were synthesized by a solvothermal method using oleic acid as the stabilizing agent. The as-prepared LaF3 nanocrystals were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD), and analysis of the upconversion spectra. The TEM results reveal that the samples present high uniformity and monodispersity and are self-assembled into a two-dimensional ordered array. Moreover, the shape, size and structure of the nanocrystals can be readily tuned by adjusting the NaF content. With increasing content of NaF, the shape of the LaF3 nanocrystals changed from particle to rod and the size gradually increased. More importantly, high NaF content favors the formation of one-dimensional nanorods. High Y b3+ and Er3+ content is beneficial to synthesizing the hexagonal phase of NaLaF4 nanocrystals. Furthermore, the TEM results show that the shape and size of the LaF3 nanocrystals can also be tuned by doping lanthanide ions, which provides a new route for size and shape control of nanocrystals. In addition, LaF3 nanocrystals co-doped with Y b3+/Tm3+ present efficient near-infrared (NIR)–NIR upconversion luminescence. More importantly, the upconversion luminescent colors can be readily tuned from blue-white to blue by adjusting the excitation power. Therefore, it is expected that these LaF3 nanocrystals with well-controlled shape, size and NIR–NIR upconversion emission have potential applications in biomedical imaging fields.
Abstract In this work, the sintering kinetics of Nd: YAG transparent ceramics under the vacuum environment was studied by the high-temperature solid phase method. The effects of different sintering temperatures and TEOS content on the densification process of Nd: YAG ceramics were studied. Meanwhile, the crystal structure of Nd: YAG transparent ceramics doped with different contents of TEOS was studied by X-ray diffractometer (XRD) and differential thermal analysis (DTA). The micrographs of ceramics samples were analyzed by scanning electron microscope (SEM). The green sample is heated to 1450~1650°C for 0~2 h at a heating rate of 20°C/min in a vacuum environment (P T ≤ 10 -6 Pa), and the shrinkage of ceramic samples was analyzed in the vacuum atmosphere by the Johnson sintering model. The sintering activation energy of Nd: YAG transparent ceramics doped with different contents of TEOS was obtained. The results indicated that the addition of TEOS promoted the densification of ceramic samples. The grain size and relative density of ceramic samples increased, and the sintering activation energy decreased with the increase of TEOS content.
From the optical absorption measurements, the Judd-Ofelt parameters were computed using Judd-Ofelt theory. According to the radiative lifetime obtained from the Judd-Ofelt parameters and the measured lifetime, the1.5μm quantum efficiency was calculated. The quenching effect of OH upon the lifetime of 1.5μm emission was investigated. From the absorption sideband measurement of glass host, the value of optical band gap was estimated. The McCumber theory was used to calculate the stimulated emission cross-section and in approximate agreement with experimental one if the emission spectrum could be obtained accurately. The gain coefficient spectra were computed.
Abstract Lu 2 O 3 doped Nd: YAG transparent ceramics were prepared by solid-state reaction and vacuum sintering. Ionic size compensation was investigated by comparing the X-ray diffraction patterns (XRD) and Raman spectroscopy (Raman) of (Nd 0.06 Lu x Y 2.94-x ) 3 Al 5 O 12 ceramics. The micrographs and element mappings of ceramics samples sintered at 1750°C for 50 h were analyzed by scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS), respectively. The emission peak intensity of 1064 nm is the largest, which corresponds to the 4 F 3/2 → 4 I 11/2 transition of Nd 3+ . Fluorescence spectra and decay curves show that the fluorescence intensity was the highest when the concentration of Lu 2 O 3 was 0.02, and the fluorescence lifetime was 193.92 µs. The elimination of lattice distortion is beneficial to the improvement of fluorescence properties, which can be attributed to ionic size compensation of Lu 3+ .
Exploring the intrinsic mechanisms of rare-earth ions entering the crystal phase has great significance for finely tuning the luminescent properties of glass-ceramics. Using Er
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