Abstract
Lanthanide nanocrystals (NCs) are the most promising luminescent materials for bioapplications, but their use is hindered by difficulties in obtaining biocompatible and photoluminescence lanthanide NCs. To solve this problem, a simple and versatile strategy was developed for improving the luminescence efficiency with the hydrophilicity of the lanthanide NCs. In this study, the effects of shell formation on structural, morphological, and optical properties (optical absorption, band-gap energy, excitation, emission, and luminescent decay time) were evaluated. To improve the luminescence efficiency and aqueous dispersion, luminescent core-NCs were encapsulated with inert NaGdF4 and amorphous silica layers. These surface coating layers significantly improved the luminescence efficiency and dispersion of the core/shell NCs in which the silica surface provides a negatively charged surface to the NCs at physiological pH. Optical properties of these NCs strongly depend on the external change of NCs, demonstrating the impact of coating in improving the luminescence efficiency. The outcomes can be ascribed to the development of surface chemical bonds between core/shell and noncrystalline SiO2 shell via Gd-O-Si bridges, activating the 'dormant' Ce3+ and Tb3+ ions on the surface of NCs. An intensive emission and good hydrophilic property from the active functional groups in solutions show a great potential for applications such as multi-analyte fluorescent biolabeling, optical biosensing, staining, display, and other optical technologies. The core/shell/SiO2 NCs showed higher nontoxicity and biocompatibility with respect to the core NCs because of biocompatible silica surface modification, facilitating entry into the living cells. Therefore, this developed synthesis approach might advance the field of biomolecule-based nanotechnology in near future. (C) 2017 Production and hosting by Elsevier B.V. on behalf of King Saud University.