Estudo das propriedades fotoluminescentes dos compósitos de MgMoO4:SrMoO4 e ZnWO4:CaWO4 obtidos pelo método de spray pirólise ultrassônico
Molybdates and tungstates are inorganic materials with immense potential in application as white light-emitting diodes (wLEDs), which are an alternative to traditional lighting sources. In this study, the synthesis and characterization of the composite MgMoO4:SrMoO4 (with molar ratios of 1:0; 0.7...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/48498 |
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| Resumo: | Molybdates and tungstates are inorganic materials with immense potential in
application as white light-emitting diodes (wLEDs), which are an alternative to traditional
lighting sources. In this study, the synthesis and characterization of the composite
MgMoO4:SrMoO4 (with molar ratios of 1:0; 0.75:0.25; 0.5:0.5; 0.25:0.75 and 0:1) and
ZnWO4:CaWO4 (with molar ratios of 1:0; 0.8:0.2; 0.6:0.4; 0.4:0.6; 0.2:0.8 and 0:1), prepared
by the ultrasonic spray pyrolysis method and their photoluminescent properties were
investigated. Using X-ray diffraction, for MgMoO4:SrMoO4 samples, the monoclinic β-
MgMoO4 phase was observed at a molar ratio of 1:0 and the tetragonal scheelite phase of
SrMoO4 at a molar ratio of 0:1. However, for ZnWO4:CaWO4 samples, the monoclinic phase
ZnWO4 was obtained at a molar ratio of 1:0 and the scheelite-type tetragonal phase of CaWO4
when the molar ratio was 0:1. The formation of a particulate material composed of both phases
was observed for the intermediate molar ratios. Scanning electron microscopy images showed
that MgMoO4:SrMoO4 and ZnWO4:CaWO4 particles show a spherical morphology formed by
primary nanoparticles. Raman scattering spectroscopy allowed the precise identification of
Raman modes for different compositions and their assignment to SrMoO4 or β-MgMoO4 and
ZnWO4 or CaWO4 modes. Bandgap energies were found in a range between 4.2 eV and 4.4 eV
for the MgMoO4:SrMoO4 samples and between 3.8 eV and 4.0 eV for ZnWO4:CaWO4,
influenced by the order/disorder structural degree of the materials. The photoluminescence
emission spectra of the particles showed neutral- and cool-white emission with high quality
white light (CRI>80%). The MgMoO4:SrMoO4 samples synthesized with a molar ratio of 1:0,
0.25:0.75 and 0.5:0.5 formed materials with potential for application in LED lamps (6,500 K)
and pure white light sources (5,500 K) while the samples of ZnWO4:CaWO4 can be considered
as promising white light sources, mainly for the sample with molar ratio 0.2:0.8, for application
in LED lamps (6,500 K). |
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