Effect of ZnS nanoparticles on the spectroscopic transitions of Ho3+ ions in sol-gel silica matrix

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 0t, which illustrate the intensities for transitions in lanthanides and actinides in solids as well as solutions follow the trend 02>04>06. Enhancement in the 02 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.

Automated summary

ZnS nanoparticles and Ho3+ co-doped silica matrices were prepared using the sol-gel method at room temperature. Structural characterizations showed the presence of ZnS nanoparticles in the co-doped silica matrices. Judd Ofelt analysis of UV-Visible absorption spectra indicated that the intensities of transitions in lanthanides and actinides followed the trend of 02>04>06. The PL emission bands of Ho3+ showed a strong dependence on ZnS nanoparticle concentration, with an optimum concentration of 0.67 M.