Navegando por Palavras-chave "Thulium"

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    Síntese e caracterização de molibdatos de cálcio dopados com Tm3+ e avaliação para aplicação em sensores de umidade
    (Universidade Federal de São Paulo (UNIFESP), 2021) Sousa, Carla Marina Dos Santos [UNIFESP]; Marques, Ana Paula De Azevedo [UNIFESP]; Universidade Federal de São Paulo
    Nanometric ceramic oxides, such as calcium molybdate (CaMoO4), with a tetragonal scheelite structure, are interesting for application in humidity sensors, due to their structural stability at high temperature, chemical and mechanical stability, in addition to their semiconductor characteristics, which can be doped with rare earths in order to improve optical, sensory, catalytic properties, among others. In this work, the synthesis of CaMoO4 doped with Tm3+ in the form of powders and tablets was investigated using the microwave hydrothermal assisted co-precipitation method for application in humidity sensors. X-ray diffractometry (XRD) and Fourier transform infrared spectroscopies (FTIR) and Raman evidence the presence of the tetragonal crystalline structure, of the scheelite type, found in all synthesized samples. Scanning Electron Microscopy (SEM) indicated a decrease in the size of the calcium molybdate particles according to the increase in the dopant concentration. The bandgap of the hydrothermally treated material at 100ºC varies little with the increase of the dopant concentration (3.9 eV and 3.7 eV, respectively for powders doped with up to 8% of thulium and with 12% Tm3+ ). In samples formed into tablets and heat treated at 1000ºC, there is a significant change in the bandgap value, with a value below 1.8 eV for the doped samples; however, the change to pure sample was subtle, and the calculated value was 3.7 eV. The projected material has yellow emission characteristics for low concentrations of thulium both at 100ºC and 1000ºC, with a pink color shift with an increase in the Tm3+ concentration. In this work, the use of molybdates doped with thulium to determine moisture was not sensitive to the method used, since all doped materials showed low capacitance signs, whereas pure molybdate was more suitable for application in sensors of humidity for presenting variation in capacitance when in the absence and presence of water.