Investigation of spectral-luminescent properties of cesium CsPb(BrCl)₃ quantum dots in fluorophosphate glasses

Within the framework of the scientific project “Investigation of spectral-luminescent properties of CsPb(BrCl)₃ quantum dots in fluorophosphate glasses” CsPbX₃ (X = Br, Cl) quantum dots were synthesized and investigated. The absorption spectra were studied using a Perkin Elmer lambda 650 double beam spectrophotometer. A Perkin Elmer LS50B spectrofluorimeter was used to obtain luminescence spectra. The temperature dependences were studied by means of an original setup, including a spectrofluorimeter, a multimode optical fiber, a cryostat and a temperature stand. The exciting light from the spectrofluorimeter lamp was focused on the input channel of the optical fiber. After leaving the channel, the radiation was collected by a lens in the focus of which was a sample fixed in a thermostat. The luminescence of the sample was collected in the opposite direction with the output to the receiver of the spectrofluorimeter, which is connected to the computer. The thermostat, in turn, was connected to a cryogenic set-top box with variable temperature, which allows adjusting the temperature in the range from 74 to 472 K. It is shown that an increase in the heat treatment time leads to an increase in quantum dots and, accordingly, to a decrease in the band gap due to the quantum confinement effect. When replacing bromine in CsPbBr₃ with chlorine, mixed CsPb(BrCl)₃ nanocrystals were obtained which leads to a shift of the absorption and luminescence bands to the short-wavelength region. Thus, by choosing different ligands for CsPbX₃ (X = Br, Cl), changing their ratio and heat treatment conditions, it is possible to adjust the wavelength of luminescence in a wide area of the visible range. The study of the dependence of the band gap width on temperature clearly showed the presence of phase transformations of the crystal structure. The sequence of phase transitions for various chemical compositions was determined, namely, the contribution of chlorine to the change in dependence in the range from 180 to 400 K. It is assumed that the main causes of luminescence quenching above 300 K are phase transitions. As a result, it is proved that fluorophosphate glass is a chemically stable medium for protecting quantum dots from external influences. The possibility of creating stable phosphors, new laser media and luminescent coatings of both white light and in the entire visible range has been obtained.

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