Photon Climb · Upconversion Explorer
June 2026 — Kyushu University created the first solid-state material to convert ordinary sunlight into UV light, using triplet–triplet annihilation in a sterically engineered organic film. Published in Nature Communications, June 23, 2026.
Visible bands absorbed · golden dots = excited T₁ states · violet burst = UV out
Triplet–Triplet Annihilation Mechanism
Upconversion converts two lower-energy visible photons into one higher-energy UV photon. It seems counterintuitive — light normally loses energy when it interacts with matter — but it works by first storing the energy of each visible photon in a long-lived molecular triplet state, then allowing two of those states to collide and pool their energy into a single UV emission. The Kyushu University team published the first solid-state version stable under natural sunlight on June 23, 2026 in Nature Communications.