Issue 10, 2024

Triplet–triplet annihilation-based photon upconversion using nanoparticles and nanoclusters

Abstract

The phenomenon of photon upconversion (UC), generating high-energy photons from low-energy photons, has attracted significant attention. In particular, triplet–triplet annihilation-based UC (TTA-UC) has been achieved by combining the excitation states of two types of molecules, called the sensitizer and emitter (or annihilator). With TTA-UC, it is possible to convert weak, incoherent near-infrared (NIR) light, which constitutes half of the solar radiation intensity, into ultraviolet and visible light that are suitable for the operation of light-responsive functional materials or devices such as solar cells and photocatalysts. Research on TTA-UC is being conducted worldwide, often employing materials with high intersystem crossing rates, such as metal porphyrins, as sensitizers. This review summarizes recent research and trends in triplet energy transfer and TTA-UC for semiconductor nanoparticles or nanocrystals with diameters in the nanometer range, also known as quantum dots, and for ligand-protected metal nanoclusters, which have even smaller well-defined sub-nanostructures. Concerning nanoparticles, transmitter ligands have been applied on the surface of the nanoparticles to efficiently transfer triplet excitons formed inside the nanoparticles to emitters. Applications are expanding to solid-state UC devices that convert NIR light to visible light. Additionally, there is active research in the development of sensitizers using more cost-effective and environmentally friendly elements. Regarding metal nanoclusters, methods have been established for the evaluation of excited states, deepening the understanding of luminescent properties and excited relaxation processes.

Graphical abstract: Triplet–triplet annihilation-based photon upconversion using nanoparticles and nanoclusters

Article information

Article type
Review Article
Submitted
31 Jan 2024
Accepted
25 Mar 2024
First published
26 Mar 2024
This article is Open Access
Creative Commons BY license

Mater. Horiz., 2024,11, 2304-2322

Triplet–triplet annihilation-based photon upconversion using nanoparticles and nanoclusters

Y. Niihori, T. Kosaka and Y. Negishi, Mater. Horiz., 2024, 11, 2304 DOI: 10.1039/D4MH00117F

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