Photochemical upconversion of near-infrared light from below the silicon bandgap

• Published in: Nature photonics Vol. 14; no. 9; pp. 585 - 590
• Main Authors: Gholizadeh, Elham M., Prasad, Shyamal K. K., Teh, Zhi Li, Ishwara, Thilini, Norman, Sarah, Petty, Anthony J., Cole, Jared H., Cheong, Soshan, Tilley, Richard D., Anthony, John E., Huang, Shujuan, Schmidt, Timothy W.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2020; Nature Publishing Group
• Subjects: 631/1647/245/2225; 639/624/1075/524; 639/624/399/1017; 639/624/399/354; Applied and Technical Physics; Chromophores; Crystals; Drug delivery; Drug delivery systems; Energy transfer; I.R. radiation; Infrared radiation; Magnetic fields; Nanocrystals; Oxygen; Photochemicals; Photonic band gaps; Photons; Photovoltaic cells; Photovoltaics; Physics; Physics and Astronomy; Quantum dots; Quantum Physics; Silicon; Singlet oxygen; Upconversion; Visible spectrum
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-020-0664-3

Photochemical upconversion is a strategy for converting infrared light into more energetic, visible light, with potential applications ranging from biological imaging and drug delivery to photovoltaics and photocatalysis. Although systems have been developed for upconverting light from photon energies in the near-infrared, upconversion from below the silicon bandgap has been out of reach. Here, we demonstrate an upconversion composition using PbS semiconductor nanocrystal sensitizers that absorb photons below the bandgap of silicon and populate violanthrone triplet states below the singlet oxygen energy. The triplet-state violanthrone chromophores luminesce in the visible spectrum following energy delivery from two singlet oxygen molecules. By incorporating organic chromophores as ligands onto the PbS nanocrystals to improve energy transfer, we demonstrate that violanthrone upconverts in the absence of oxygen by the triplet–triplet annihilation mechanism. The change in mechanism is shown by exploiting the magnetic field effect on triplet–triplet interactions. Photochemical upconversion of light with photon energy below the silicon bandgap has remained elusive, but the feat has now been demonstrated using PbS semiconductor nanocrystals and violanthrone.