NaYF₄ :Yb,Er/NaYF₄ Core/Shell Nanocrystals with High Upconversion Luminescence Quantum Yield.

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Upconversion nanocrystals are crucial for applications requiring light emission at higher energies than absorbed.
• Developing efficient and scalable synthesis methods for upconversion nanocrystals is an ongoing research area.
• Core/shell nanostructures offer enhanced optical properties compared to their core-only counterparts.

Purpose of the Study:

• To synthesize upconversion core/shell nanocrystals with controlled sizes.
• To investigate the impact of particle size on photoluminescence quantum yield (PLQY).
• To compare the efficiency of synthesized nanocrystals with bulk upconversion phosphors.

Main Methods:

• Modified synthesis procedure using anhydrous rare-earth acetates.
• Preparation of NaYF4:Yb,Er core nanocrystals with an inert NaYF4 shell.
• Fabrication of core/shell particles with varying mean sizes (15-45 nm).
• Absolute photoluminescence quantum yield measurements at different excitation power densities.

Main Results:

• Core/shell nanocrystals with a mean size of 45 nm exhibited PLQY comparable to microcrystalline upconversion phosphor powder.
• Smaller core/shell nanocrystals (down to 15 nm) showed a moderate decrease in PLQY.
• The PLQY of 15 nm particles was reduced by a factor of 3 at high power densities (100 W/cm²) and 10 at low power densities (1 W/cm²).

Conclusions:

• The modified synthesis procedure effectively produces upconversion core/shell nanocrystals with tunable sizes.
• Larger core/shell nanocrystals achieve high photoluminescence quantum yields, nearing bulk material performance.
• Size-dependent efficiency reduction in smaller nanocrystals is observed, providing insights for future material design.