UCNPs can penetrate deeper into biological tissues and reduce photodamage. For example, UCNPs excited at 808nm can minimize tissue overheating effects and autofluorescence interference in biological applications. At the same time, the core-shell structure design (such as NaYF4:Yb³⁺/Er³⁺) not only improves the quantum efficiency to 5%, but also enhances biocompatibility through surface modification, which is suitable for in vivo imaging and treatment. From optogenetic regulation to tumor photodynamic therapy (PDT), UCNPs show the potential for interdisciplinary integration.

Design and Optimization Strategy of High Quantum Yield UCNPs
1. Material innovation: The surface quenching effect is suppressed by inert shell coating (such as NaYF4:Yb³⁺@NaLuF4:Yb/Er), and the quantum efficiency is significantly improved. Multilayer core-shell design (such as NaYF4:Yb/Nd@NaLuF4:Yb/Er@NaYF4:Nd@SiO2) further optimizes the energy transfer path and enhances the luminescence intensity by a hundred times.

Yb³⁺ acts as a sensitizer to enhance near-infrared absorption, and Er³⁺ or Tm³⁺ regulates the emission wavelength. Multi-element co-doping (such as Gd³⁺/Lu³⁺) can improve the crystal quality and increase the integrated luminescence intensity by 1.66 times.

2. Surface modification: Hydrophilic coating improves dispersibility and is suitable for biological fluid environments. Targeted molecular coupling (such as antibodies) achieves lesion-specific aggregation and improves treatment accuracy.

3. Dye sensitization technology: Organic dyes (such as pyrrolopyrrole dione derivatives) are combined with UCNPs to broaden the absorption range to the near infrared, increase the luminescence intensity by 20 times, and have photothermal/photodynamic synergistic therapeutic effects.

Solar cells: This technology represents the solution for surpassing the efficiency limitation barrier

The addition of Upconverting nanoparticles enables solar cells to produce more efficient photocurrents by transforming non-absorbable low-energy photons into usable high-energy photons. β-NaYF4 crystals with lanthanide doping serve as highly effective Upconverting hosts because their hexagonal phase structure combines high symmetry with low phonon energy. Research demonstrates that photovoltaic devices using Er³⁺/Yb³⁺ co-doped β-NaYF4 exhibit ultra-high flux Upconverting along with a standardized external quantum efficiency of 3.38×10⁻² cm²/W. To further enhance the light-harvesting capability, the combination of silicon nanoparticle film and UCNPs was proposed: The localized surface plasmon resonance effect from silicon nanoparticles boosts UCNPs’ fluorescence intensity and decreases parasitic absorption losses resulting in a 38% gain in dye-sensitized solar cells’ photoelectric conversion efficiency. In addition, the core-shell structure design (such as NaYF4: The core-shell architecture NaYF4:Yb³⁺/Tm³⁺@NaYF4 enhances Upconverting luminescence intensity by 240 times through optimized energy migration paths while surface passivation technology like the inert NaYF4 shell prevents surface quenching effects and preserves core luminescence properties. These combined technologies establish the groundwork necessary for commercial applications. Quantum cutting layers like Yb³⁺-doped CsPbCl3 improve perovskite solar cells by transforming ultraviolet-blue absorption into near-infrared emission achieving nearly 200% theoretical quantum efficiency.

Optogenetics: A new paradigm for non-invasive neuromodulation

Near-infrared light (such as 808 nm) is an ideal excitation light source for optogenetic regulation due to its deep tissue penetration and low phototoxicity. UCNPs can activate light-sensitive channel proteins (such as ChR2) in neurons by absorbing near-infrared light and converting it into blue/green light (such as 470 nm), achieving wireless, low-inflammatory, precise neuromodulation. To improve targeting, molecules such as folate receptor ligands can be coupled to the surface of UCNPs to enable them to aggregate specifically in the tumor area. Combined with real-time imaging techniques (such as photoacoustic imaging), this nanosystem can dynamically monitor the therapeutic effect: for example, Au-Ag alloy/NaYF4:Yb,Tm composite film achieved a 180-fold increase in Upconverting luminescence intensity through the plasma enhancement effect, significantly improving the imaging contrast. In addition, near-infrared excited UCNPs can also be used for photodynamic therapy to directly kill tumor cells by releasing reactive oxygen species (ROS). Experiments have shown that nanobubbles (NB)-encapsulated UCNP-CNQD composites can efficiently generate singlet oxygen, while feedback of the treatment process through fluorescence signals. This multimodal platform provides a high-precision, low-damage innovative tool for neuroscience research and tumor treatment.

Singlet Oxygen Generation and Tumor Treatment Applications
UCNPs convert near-infrared light into visible light, activate photosensitizers (such as phthalocyanine derivatives) to generate singlet oxygen (¹O₂), and kill tumor cells. The singlet oxygen quantum yield can reach up to 84%. Nanosystems (such as D-A-D structure IID-ThTPA) have synergistic photothermal/photodynamic effects, inhibiting tumor growth by 90% in vivo experiments. The hypoxic tumor environment limits the effect of PDT, and the efficacy is enhanced by nano-oxygen carriers or combined with chemotherapy drugs (such as Pacloxacil).

There are more research and application directions for UCNPs in the future. For example, aza BODIPY dyes balance efficiency and biocompatibility. Combine optogenetic regulation, drug controlled release and real-time temperature monitoring. Materials science, neurobiology and energy engineering jointly promote the industrialization of UCNPs.