Abstract
ZnS NPs and Ho3+ co-doped silica matrices are prepared by room temperature sol-gel method. The fabricated matrices are characterized structurally by X-ray diffractometry, Transmission electron microscopy, Energy dispersive X-ray analysis and Fourier transform infrared spectroscopy. Structural studies reveal the presence of ZnS NPs in the Ho3+ co-doped silica matrices. Judd Ofelt analysis of UV–Visible absorption spectra shows that the phenomenological Judd Ofelt intensity parameters Ωt, which illustrate the intensities for transitions in lanthanides and actinides in solids as well as solutions follow the trend Ω2>Ω4>Ω6. Enhancement in the Ω2 parameter with ZnS NP concentration indicates higher asymmetry and a stronger covalent environment of Ho3+ ions in the studied matrix, compared to some popular hosts. The four distinct PL emission bands of Ho3+ observed in the studied matrices show a strong dependence on ZnS NP concentration, with 0.67 M of ZnS as the optimum concentration. The enhancement in the PL emissions with ZnS NPs is attributed to the network modification and sensitization of Ho3+ ions by the NPs. Sensitization through energy transfer also increases the lifetime of the excited state, as observed from the PL decay study. The decrease of PL emission beyond optimum ZnS concentration is most likely due to the self-quenching of ZnS NPs. The upconversion study shows enhancement in Ho3+ luminescence up to 14 times with ZnS co-doping; indicating the viability of the fabricated matrix for their application in UC devices as well.
Published Version
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