| Summary: | Photovoltaic solar cells can generate electricity directly from sunlight without emitting greenhouse gases. This makes it an ideal candidate as a large scale energy producer. However, the sub-bandgap loss problem of solar cells limits its efficiencies. Up-conversion mechanism could minimize this sub-bandgap loss. Thus a high efficient up-conversion material is necessary. The project aims to synthesize phosphor in nano sizes with in depth study on the factors that influence the crystal growth process and the up-conversion photoluminescence (PL).
The Y2O3: Er3+, Yb3+ phosphors were synthesized via hydrothermal / solvothermal method with varied surfactant (oleic acid) concentration, followed by calcinations to change its crystal structure from hexagonal to cubic bixbyite. FESEM, TEM, XRD and PL spectra were used to characterize these products. Three products with different size (40nm – 2um) and shape were obtained, namely, nanoparticle, nanobelt, and microrod. These differences were largely controlled by the concentration of surfactant and different surface energy of nuclei facets. The higher surface energy facets would growth faster than the others, but the growth could be inhibited by surfactants which prefer to bind to higher surface energy facets.
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