Enhancing NIR emission in ZnAl2O4:Nd,Ce nanofibers by co-doping with Ce and Nd: a promising biomarker material with low cytotoxicity

Abstract

Development of new near infrared luminescent (NIR) emitters improves our understanding of their fundamental structure–property relationships. The ability to use efficient energy transfer to convert ultraviolet or visible light photons to enhance the NIR emission has attracted a great deal of attention in down-conversion applications. Taking advantage of the sol–gel impregnation process and growth of materials along a support or template, core–shell structured nanofibers of ZnAl₂O₄ – based ceramic doped with cerium and neodymium were synthesized with the help of an elaborate facile and cost-efficient strategy. The color-tunable emissions make this material a suitable host for a wide range of applications, e.g., bio-imaging, security markers, imaging devices, optical coatings, and solar cells. This research correlates the defects and the remarkable optical properties of the developed structures. Specified conditions of sol–gel processing combined with the incorporation of rare-earth elements in various concentrations provide the possibility of tuning the ratio between Ce³⁺ and Ce⁴⁺ in the nanofibers with an average diameter of 50 nm and, therefore, their functional response. It is important to clarify the role of trivalent and tetravalent cerium cations in the modulation of NIR emission to establish the luminescence mechanism. The NIR emitter luminescent compound ZnAl₂O₄:Nd,Ce, which adopts a spinel-type structure, is studied using the X-ray absorption near-edge structure technique. For the first time, this study reveals the energy transfer from Ce³⁺ to Nd³⁺ and the enhancement of the NIR emission due to the presence of Ce⁴⁺ in the ZnAl₂O₄:Nd,Ce spinel compound. Cytotoxicity analyses suggest the viability of the synthesized nanofibers, which opens new avenues in bio-imaging applications.