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Photoelectric Effect

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When light of a particular wavelength strikes a metal surface, electrons are emitted. This is called the photoelectric effect. The minimum frequency of light that can cause such emission of electrons is called the threshold frequency, which is specific to the metal. Light with a frequency lower than the threshold frequency, even if it is of high intensity, cannot initiate the emission of electrons. However, when the frequency is higher than the threshold value, the number of electrons ejected...

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Near-Infrared to Visible Photon Upconversion with Gold Quantum Rods and Aqueous Photo-Driven Polymerization.

Zhongyu Liu¹, Xiaolei Hu¹, Lianshun Luo¹

¹Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.

Journal of the American Chemical Society

|July 28, 2025

Summary

This summary is machine-generated.

Atomically precise gold quantum rods enable efficient near-infrared (NIR) to visible light conversion through triplet-triplet annihilation upconversion (TTA-UC). This breakthrough advances applications in energy, biomedicine, and materials science.

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Area of Science:

Materials Science
Nanotechnology
Photochemistry

Background:

Triplet-triplet annihilation upconversion (TTA-UC) converts near-infrared (NIR) to visible light, crucial for energy and biomedical applications.
Efficient NIR sensitizers are essential for TTA-UC but remain a significant challenge.

Purpose of the Study:

To develop a high-performance photosensitizer for NIR-to-visible TTA-UC.
To create an aqueous-compatible TTA-UC system for advanced photopolymerization and biomedical applications.

Main Methods:

Synthesized an atomically precise gold quantum rod, Au42(PET)32, as an NIR sensitizer.
Paired the gold quantum rod with TES-ADT as an annihilator for TTA-UC.
Encapsulated Au42/TES-ADT upconversion nanodroplets within a silica shell to create Au42/TES-ADT@SiO2 nanoparticles (NPs).

Main Results:

Achieved a 6.7% quantum yield for NIR-to-visible TTA-UC.
Observed a 0.5 eV anti-Stokes shift and a low threshold intensity of 90 mW/cm2.
Demonstrated efficient photoinduced atom-transfer radical polymerization (photo-ATRP) and hydrogel formation in water using the silica-coated NPs.

Conclusions:

Atomically precise gold quantum rods serve as effective photosensitizers for NIR-to-visible TTA-UC.
The developed silica-encapsulated NPs provide aqueous compatibility for TTA-UC applications.
This system presents a versatile platform for NIR-driven photopolymerization, solar energy utilization, and noninvasive biomedical applications.