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In this study, Yb:YAG-nanocrystal-doped silica glass with high transmission and excellent spectral properties was successfully prepared using a modified sol–gel method. The X-ray diffraction (XRD), micro-Raman spectroscopy, electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), and high-resolution TEM (HR-TEM) analyses confirmed that the Yb:YAG nanocrystals, with their low content, homogeneous distribution, and small crystal size, directly crystallized into the silica glass network without annealing treatment. In contrast with conventional microcrystalline glass having large particles (>0.1 μm) and a large particle content, nanocrystalline glass with a homogeneous distribution and sizes of ~22 nm had higher optical transmittance and better spectral properties. Compared with Yb3+ doped silica glass without nanocrystals, the Yb:YAG-nanocrystal-doped silica glass had a 28% increase in absorption cross-section at 975 nm and a 172% enhanced emission cross-section at 1030 nm without any changes in the spectral pattern of the Yb3+ ions in the silica glass. Meanwhile, the Yb:YAG-doped silica glass with large size and high optical quality was easily prepared. Therefore, the Yb:YAG-nanocrystal-doped silica glass is expected to be a promising near-infrared laser material.

A high phosphorus Er3+/Yb3+ co-doped silica (EYPS) fiber core glass was prepared using the sol-gel method combined with high-temperature sintering. The absorption spectra, emission spectra, and fluorescence decay curves were measured and compared in temperatures ranging from 300 to 480 K. Compared to 915 and 97x nm, the absorption cross-section at ~940 nm (~0.173 pm2) demonstrates a weaker temperature dependence. Hence, the 940 nm pump mechanism is favorable for achieving a high-power laser output at 1.5 μm. Additionally, the double-exponential fluorescence decay of Yb3+ ions and the emission intensity ratio of I1018nm/I1534nm were measured to evaluate the energy transfer efficiency from Yb3+ ions to Er3+ ions. Through the external heating and active quantum defect heating methods, the emission intensity ratios of I1018nm/I1534nm increase by 30.6% and 709.1%, respectively, from ~300 to ~480 K. The results indicate that the temperature rises significantly reduce the efficiency of the energy transfer from the Yb3+ to the Er3+ ions.

Functionalized layered double hydroxides (LDHs) based on a multimodifier system composed of itaconic acid (ITA) and titanate coupling agent (NDZ-201) were designed and fabricated in this paper with the aim to develop high-performance fire retardant paper. The structure of LDHs were characterized using Fourier transform infrared spectroscopic analysis, X-ray diffraction analysis, thermogravimetric analysis (TGA), scanning electron microscopic analysis, cone calorimetry, and laser particle size analysis. The results showed that carbonate anions were partially replaced by ITA, whereas the titanate coupling agent was attached to the surfaces of the hydrotalcites. The limiting oxygen index (LOI), TGA curves, total heat release rate (THR), and heat release rate (HRR) indicated that as the addition of hydrotalcites increased, the modified LDHs' LOI value and thermal stability noticeably increased compared to the unmodified hydrotalcites, and the HRR and THR of the material decreased. When the addition amount was 25%, the LOI of ITALDHs was 26.9%. However, the Mg-Al hydrotalcites adversely affected the strength index of flame-retardant paper; the modified hydrotalcites clearly reduced this effect, and the whiteness of paper increased and reached 83%. [ABSTRACT FROM AUTHOR]