Sep 20, 2025

Plasmonic design sparks 2440 fold photon upconversion in 2D layers

Scientists report a record 2440 fold boost in two photon upconversion from 2D excitons, opening new paths for advanced photonic devices and energy research.

(Nanowerk News) Scientists in China have reported a record breaking boost in the ability of 2D materials to convert low energy photons into higher energy ones, a process called photon upconversion that could power advances in photonics and energy technologies.

Photon upconversion is central to energy conversion and optical applications, but in two dimensional semiconductors like transition metal dichalcogenide monolayers it often suffers from inefficiencies. Researchers have been searching for ways to make the process more efficient, particularly through two photon upconversion, which can reveal hidden “dark states” of excitons, the bound pairs of electrons and holes that dominate the behavior of these materials.

A team at Nankai University has now achieved a 2440 fold amplification in two photon upconversion from 2D excitons. Their breakthrough was published in Light: Science & Applications ("Giant two-photon upconversion from 2D exciton in doubly-resonant plasmonic nanocavity"). The researchers built a plasmonic device using gold nanocubes and a WS₂ monolayer. By carefully matching the device’s resonances to the excitons’ excitation and emission bands, they were able to dramatically amplify light emission.

Time resolved photoluminescence experiments confirmed that the nanocavity shortened exciton lifetimes by enhancing spontaneous emission, a phenomenon known as the Purcell effect. Acting like a nanoscale antenna, the cavity also improved light directionality, allowing far more efficient light collection.

Further testing showed that thermal tuning could push the amplification even higher, beyond 3000 at elevated temperatures. Compared to other optical effects in the same system, such as second harmonic generation or conventional photoluminescence, two photon upconversion showed by far the strongest enhancement, pointing to the unique role of the double resonance mechanism.

The results not only establish new records for photon upconversion but also lay the groundwork for compact, cost effective devices that could revolutionize nonlinear photonics and provide new ways to probe the fine structure of excitonic states.

Source: Changchun Institute of Optics, Fine Mechanics And Physics (Note: Content may be edited for style and length)