In this study, Er 3+ /Al 3+ co-doped silica glasses with various Al/Er ratios ranging from 0 to 200 and a constant Er 2 O 3 amount were prepared using the sol-gel method combined with high-temperature vacuum sintering. The absorption, emission spectra, and fluorescence lifetime of Er 3+ ions were recorded and the absorption and emission cross sections were calculated. Using Raman, 27 Al and 29 Si magic angle spinning nuclear magnetic resonance (MAS-NMR), 27 Al triple-quantum (TQ)-MAS-NMR, and electron paramagnetic resonance (EPR) spectroscopies, the physical and optical properties were correlated with the glass structural modifications due to the Al/Er ratio change. With the increase in the Al/Er ratio, the content of Al 3+ ions around the Er 3+ ions gradually increased. Meanwhile, the AlO 5 and AlO 6 polyhedrons increased at the expense of the AlO 4 and SiO 4 tetrahedrons, which resulted in an improved symmetry and better ionic Er–O bonds. These structural changes led to the site-to-site variations in the Er 3+ local environment and the changes in the ligand field strength of the Er–O bonds. This, in turn, resulted in the inhomogeneous broadening of the absorption and emission spectra, with a blue shift of both absorption and emission peaks and a decrease in both absorption and emission at 1.53 μ m. With the increase in Al/Er ratio, the full width at half maximum (FWHM) of the emission increased from 27.2 to 54.3 nm. The FWHM × emission cross section ( σ e m i ) parameter for evaluating broadband amplification behavior was 30.1 × 10 −20 cm 2 · nm. This work reveals the close relationship between the glass structure and the spectroscopic properties of Er 3+ ions and provides an important reference for the design of broadband amplifier materials in the field of optical communication.
Detection of NO 2 attracted increasing interest to check the air quality and monitor exhaust emission of combustion facilities. In this study, the flame spray pyrolysis (FSP) method was used to prepare the La-doped WO 3 nanoparticles as NO 2 sensing materials for the first time. The FSP-made La-doped WO 3 nanoparticles showed that the doped La atoms were dispersed homogeneously on WO 3 particles in the form of La 2 O 3 . It was observed that in the concentration range of 150–1200 ppb at 125 ℃ , the WO 3 sensing responses were enhanced by La doping from 2.5 at% to 10 at%, and exhibited the highest sensing response when the La doping ratio was 7.5 at%. The 7.5 at% La-doped WO 3 shows the highest response (74.2) toward 900 ppb NO 2 at 125 ℃ with response/recovery times of 23 and 35 s. Then, the high-resolution XPS spectra and sensing mechanism were combined to investigate the La-doping effects, it can be found that the enhancement of La doping might result from the enriched vacancy oxygen and more absorption sites, as well as the p-n heterojunction that drives more electrons to react with NO 2 . Moreover, the sensor using 7.5 at% La-doped WO 3 presented an excellent anti-interference performance to single NH 3 , SO 2 , CO, CO 2 , and CH 4 , but were disturbed by ppm-level NH 3 and SO 2 coexisted with NO 2 . It also exhibited good resistance to RH fluctuation and good stability.
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