Hybrid luminescent systems based on rare-earth-doped upconversion nanoparticles Mechanisms and wide range temperature sensing

Lanthanide-doped upconversion nanoparticles (UCNPs) are promising candidates for advanced optical applications, yet their efficiency remains a critical challenge. This thesis presents a systematic study to enhance the luminescence and functionality of UCNPs through energy transfer engineering, host lattice design, and nanocomposite strategies.
The energy transfer mechanism in the Yb³⁺-Ho³⁺ system by tailoring core-shell-shell nanostructures is explored and optimized, which enable efficient cooperative sensitization upconversion (CSU), especially at cryogenic temperatures. Building on this, a photonic nanostructure incorporating polymethyl methacrylate (PMMA) opal photonic crystals is designed to further enhance the emission of this system via photonic bandgap modulation, resulting a 4,300-fold upconversion luminescence enhancement at 80 K and enabling high-sensitivity cryogenic thermometry.
Next, a highly sensitive temperature probe based on a heavily doped Er³⁺ system is developed, where cross-relaxation effects provide reliable and ultra-sensitive luminescence thermometry. To further boost the upconversion performance, alkaline-earth-based cubic host matrices (M_1-xErF_2+x, M = Ca, Sr, Ba) are introduced to modify the host-dopant interactions. Among them, SrErF₅@SrYF₅ nanoparticles exhibit over 8-fold enhanced emission and pronounced thermal responsiveness.
Finally, a novel composite is constructed by integrating cubic-phase BaYbF₅:Tm³⁺ UCNPs with CsPbBr₃ perovskite quantum dots. The excellent lattice match facilitates energy transfer and produces dual-mode optical output, demonstrating potential in multifunctional nanophotonics.
Together, this work advances the design of high-performance UCNP platforms and broadens their applications in low-temperature sensing, optical devices, and hybrid nanophotonic systems.