Spectroscopic characterization of NaYF4: Tm3+/Pr3+ microcrystals showing concurrent emission in UV and NIR spectral ranges


The optical spectroscopy of trivalent lanthanide ions has drawn attention since 1880s, owing to the fact that their robust energy levels stack up as a multi-step-ladder resembling structure. This remarkable feature allows them to absorb photons and manage their energy via radiative and non-radiative f-f transitions. Depending on the mechanism parameters, e.g. sufficiently long lifetimes of excited states, the emitted photons could be lower or higher in energy than the input photons. Furthermore, the energy conversion processes are highly likely to occur simultaneously, which results in emissions observed across various spectral ranges, i.e. ultraviolet (UV), visible (VIS), and near-infrared (NIR). Not to mention, the ability to predict the emission bands of trivalent lanthanide ions when incorporated into low phonon energy host matrices (e.g., LiYF4 or NaYF4) facilitates the design of lanthanide-based bimodal optical materials. These advancements hold promise for the development of state-of-the-art photovoltaic instruments, optical amplifiers, telecommunications systems, and theranostic devices [1]. Recently, our scientific focus has shifted towards fluoride matrices doped with Tm3+ ions, known for exhibiting numerous emission bands in the UV, VIS, and NIR spectral regions. Their robust electronic structure enables multiple energy migration processes, such as up-conversion or quantum cutting. While pairs like Tm3+/Yb3+ and Tm3+/Er3+ have been exten-sively studied for emission enhancement [2], [3] information on the Tm3+/Pr3+ pair remains scarce. Therefore, we have chosen to explore it in more detail. Microcrystalline NaYF4 samples synthesized via solid-state techniques were characterized under VIS laser radiation exci-tation. The VIS-to-UV up-conversion emission, Stokes VIS-to-VIS emission, and VIS-to-NIR down-conversion were collected and analyzed. Additionally, luminescence decay curves were recorded for the selected emission bands. These findings contribute to a better understanding of photon management processes in Tm3+/Pr3+ co-doped materials, which is crucial for designing devices that utilize concurrent emission in both UV and NIR regions.

2nd International Conference on Advanced Materials for Bio-Related Applications