UV-Vis-NIR Photoluminescence Spectroscopy

Photoluminescence (PL) is widely applied to investigate surfaces and surface chemical phenomena with a high degree of sensitivity. The technique provides extremely rich information when applied to the study of photoluminescence sites on bulk oxides with a large surface to volume ratio on sites located on the surface of a support, for example oxide-supported catalysts on sites that can be modified by thermal treatments (calcination, reduction, etc.) and when the local environment of the emitting sites is altered by the adsorption of molecular probes. By way of introduction, basic photophysical aspects essential for the rationalization of PL data will be summarized. 

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The particle size and composition of the dispersed phase of the colloidal dispersions were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis and photoluminescence (PL) spectroscopy. The TEM experiments were carried out on a LEO-906 device. The samples were obtained by placing a drop of the colloidal solution in toluene on TEM copper grid coated with a thin layer of carbon and evaporated in air at room temperature. XRD patterns of powders were obtained by a diffractometer HZG 4A using CuKa radiation. The UV-vis spectra of the colloidal dispersions were recorded using Cary 500 Scan UV-VIS-NIR spectrophotometer with a 1-cm quartz cell. The PL spectra were recorded using a SFL-1211A spectrofluorimeter. 

Luminescence Spectroscopy. Photoluminescence measurements were performed with the aid of a Fluorolog3 spectro-fluorometer Fl3—22 (Horibajobin Yvon) equipped with double Czerny—Turner monochromators, a 450 W xenon lamp and a R928P photomultiplier with a photon counting system. Cooling down to 10 K was achieved by a closed cycle He cryostat (Janis Research). All emission spectra were corrected for the photomultiplier sensitivity and all excitation spectra for the intensity of the excitation source. To avoid any contamination of water on the sample s surfaces, we carried out the measurements in silica ampules with extreme purity which show no luminescence of the ampules itself. Reflection spectra were recorded on a Cary 5000 UV—vis—NIR spectrophotometer (Varian), which were corrected for both the lamp intensity and the photomultiplier sensitivity. 

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