Synthesis and up-conversion of core/shell SrF2:Yb3+,Er3+@SrF2:Yb3+,Nd3+ nanoparticles under 808, 975, and 1532 nm excitation wavelengths
Dominika Przybylska, Tomasz Grzyb
Abstract
Sensitization of nanoparticles (NPs) by appropriate lanthanide ions is crucial for the obtained spectroscopic properties. Nd3+ ions can absorb light at around 808 nm, allowing for deep tissue imaging, Yb3+ ions can be effectively excited by 975 nm radiation which is utilized in many areas, e.g. in anti-counterfeit applications, while Er3+ ions are capable of absorption around 1532 nm, which in turn, is important for solar energy conversion. Here, we describe a method for Nd3+ and Er3+ ions isolation in NPs by the synthesis of core/shell structures. As an alternative to the most commonly used core/shell thermal decomposition synthesis procedures, our products were obtained in water by a hydrothermal method. SrF2:Yb3+,Er3+@SrF2:Yb3+,Nd3+ NPs with sizes between 30 and 60 nm showed intense green to yellowish-red luminescence in the visible range, due to Er3+-doping. Yb3+ played the role of bridging ions, transferring energy absorbed by Nd3+ ions between the shell and core phases, limiting, in the same way, cross-relaxation between Nd3+ sensitizer ions and Er3+ luminescence centers. Structure, morphology and spectroscopic properties were investigated, revealing interesting processes taking place in the prepared NPs.