Transmitter-Free Interfacial Sensitization in ZnSe/ZnS Quantum Dots Enables Efficient Upconversion

Area of Science:

• Materials Science
• Photochemistry
• Quantum Dots

Background:

• Triplet-triplet annihilation upconversion (TTA-UC) is vital for converting visible light to UV.
• Design principles for efficient interfacial triplet energy transfer (TET) in TTA-UC are not fully understood.
• Quantum dots (QDs) offer tunable properties for TTA-UC applications.

Purpose of the Study:

• To compare transmitter-mediated and direct assembly strategies for visible-to-UV TTA-UC using ZnSe/ZnS QDs.
• To investigate the impact of different annihilators (DTBN and TP) on TTA-UC efficiency.
• To establish design principles for high-performance TTA-UC materials.

Main Methods:

• Utilized ZnSe/ZnS core/shell quantum dots for TTA-UC.
• Compared transmitter-mediated (using BCA) and transmitter-free direct assembly sensitization.
• Employed time-resolved photoluminescence to analyze interfacial TET rates.
• Investigated two high-triplet-energy annihilators: 2,6-di-tert-butylnaphthalene (DTBN) and p-terphenyl (TP).

Main Results:

• DTBN showed faster interfacial TET (0.030 ns⁻¹) compared to TP (0.022 ns⁻¹) in direct assemblies.
• TP exhibited a significantly higher fluorescence quantum yield (54.59%) than DTBN (4.77%).
• The direct ZnSe/ZnS-TP assembly achieved a maximum UC efficiency of 7.9%, surpassing BCA-mediated (6.9%) and DTBN-based (≤1.5%) systems.

Conclusions:

• Annihilator fluorescence quantum yield is a critical factor for high TTA-UC efficiency.
• Direct assembly of ZnSe/ZnS QDs with p-terphenyl provides superior visible-to-UV upconversion.
• Simplifying donor-acceptor interfaces and prioritizing annihilator emissivity are key design strategies for efficient TTA-UC.