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Transient photoinduced phenomena in graphitic carbon nitride as measured at nanoseconds resolution by step-scan FTIR
摘要： Transient FTIR measurements were performed on graphitic carbon nitride using a step-scan method, facilitating temporal resolution of a few nanoseconds. Variations in the location and the intensity of specific peaks and emerging of new peaks were observed during the first 170 nanoseconds after excitation. A comparison was made between graphitic carbon nitride prepared at two temperatures: 510 °C and 650 °C. The material prepared at 650 °C revealed very strong non-specific absorption beginning 35 nanoseconds after excitation and lasting for 20 nanoseconds. This phenomenon, termed “IR-blackening” was observed neither in g-C3N4 prepared at 510 °C nor in g-C3N4 prepared at 650 °C that was exposed to hole scavengers (ethanol and benzyl alcohol). In contrast, exposure of material prepared at 650 °C to an electron scavenger (methyl viologen) hardly alter the “IR-blackening” phenomenon. The results were explained by a mechanism, predicting higher reductive activity for materials having imperfect heptazine polymerization, as indeed was found in the photocatalytic degradation of 4-nitrophenol.
关键词： Photocatalysis,IR- blackening,Step-scan,graphitic carbon nitride,Transient FTIR
更新于2025-09-23 15:21:21
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Low-power laser-induced absorption in YSZ ceramics through formation of F-centers
摘要： Infrared lasers, especially those having a wavelength of either 10.6 μm or 1.06 μm are of great technological importance. Unfortunately, many dielectric materials, such as common ceramics absorb very poorly the latter wavelength since it falls within their large bandgap. However, some materials do not follow this general trend and strongly absorb moderate-energy-density (10–100 J/cm2) laser radiation of both types, although their bandgap extends into the infrared far beyond 1 μm and contains no intrinsic energy levels. The present study was motivated by the observation that IR-laser melting of some of these oddly behaving materials seems to be accompanied by appearance of strong visible absorption. The evolution of the optical properties and crystal structure of one of them, YSZ, as well as that of alumina, having a regular behavior, was studied by optical microscopy, SEM, XRD, Raman spectroscopy, optical spectroscopy and DRIFTS. As a result, it was shown for the first time that the melting of YSZ by 1.06 μm laser radiation is only possible due to F-centers forming in the tetragonal structure of the material, giving rise to a broad absorption continuum, which covers the entire bandgap of the material, including that wavelength, and when F-centers generation is inhibited, melting does not occur anymore. In order to explain that phenomenon, the possibility of multiple energy levels arising within the band gap because of F-center coupling and anisotropy was studied theoretically. Thus, a simple model was constructed, representing F-center clusters as coupled potential wells with variable separations between them and variable effective electron mass due to anisotropy. The model with just two wells produced multiple energy states distributed throughout the bandgap of the material, thus offering support for said hypothesis.
关键词： Absorption,Blackening,Zirconia,F-center,Ceramics,Laser
更新于2025-09-12 10:27:22