Optimization of upconversion and downshifting efficiency in core@shell@shell LDNPs through impurity doping and inhibition of cation intermixing

Abstract

Designing lanthanide-doped nanoparticles (LDNPs) with controlled emission properties is crucial for their use in advanced optical applications such as bioimaging, sensing, and photonics. In this study, we present a core@shell@shell LDNP structure constructed to optimize fluorescence in both the visible and NIR-II regions through precise morphological control and dopant modulation. The architecture consists of a NaYF4:Yb3+, Er3+ core with impurity doping of Ce3+, coated with an active NaYbF4:Er3+ inner shell and an inert NaGdF4 outer shell. This specific host combination, employed together for the first time, was chosen to effectively manage energy transfer processes and suppress cation intermixing. By systematically tuning reaction parameters and shell thicknesses, we achieved a significant enhancement in dual-mode emission: similar to 27-fold increase in visible and similar to 5-fold improvement in NIR-II emission under 980 nm excitation at low power density (0.15 W cm(-2)). The optimized core@shell@shell LDNPs further exhibited a visible photoluminescence quantum yield (PLQY) of 0.98 % at 2 W cm(-2), confirming the high upconversion efficiency. This work demonstrates how thoughtful control over material design through dopant placement, shell architecture, and reaction conditions can lead to multifunctional LDNPs with tailored optical behavior, enabling their broader application in the design of efficient and versatile luminescent nanoplatforms.