Bright upconversion over extended temperatures enabled by an organic surface layer

Area of Science:

• Materials Science
• Nanotechnology
• Photonics

Background:

• Lanthanide-doped nanocrystals offer tunable photon frequency upconversion.
• Low luminescence efficiency and thermal quenching limit their practical use.
• Surface defects and high-energy oscillators contribute to energy dissipation.

Purpose of the Study:

• To enhance upconversion luminescence efficiency across a wide temperature range.
• To investigate the mechanism of luminescence enhancement via surface modification.
• To develop temperature-responsive upconversion materials for advanced applications.

Main Methods:

• Surface coordination of small organic molecules onto NaGdF4:Yb3+/Tm3+ nanocrystals.
• Characterization of upconversion luminescence properties at varying temperatures and humidity.
• Mechanistic studies involving defect passivation and surface oscillator isolation.

Main Results:

• Organic surface coordination significantly boosted upconversion luminescence.
• The enhancement effect intensified with increasing temperature, especially in humid conditions.
• An anomalous optical response to thermal stimuli was observed, enabling thermochromic switching.

Conclusions:

• Surface coordination is a versatile strategy to overcome thermal quenching and improve upconversion efficiency.
• The developed materials exhibit temperature-dependent optical properties suitable for anti-counterfeiting and logic encryption.
• This work opens avenues for designing advanced functional nanomaterials with tailored optical responses.