Feng, J., Alves, J., de Clercq, D. M. & Schmidt, T. W. Photochemical upconversion. Annu. Rev. Phys. Chem. 74, 145–168 (2023).
Wen, S. et al. Future and challenges for hybrid upconversion nanosystems. Nat. Photon. 13, 828–838 (2019).
Schulze, T. F. & Schmidt, T. W. Photochemical upconversion: present status and prospects for its application to solar energy conversion. Energy Environ. Sci. 8, 103–125 (2015).
Ravetz, B. D. et al. Photoredox catalysis using infrared light via triplet fusion upconversion. Nature 565, 343–346 (2019).
Khnayzer, R. S. et al. Upconversion-powered photoelectrochemistry. Chem. Commun. 48, 209–211 (2012).
Sanders, S. N. et al. Triplet fusion upconversion nanocapsules for volumetric 3D printing. Nature 604, 474–478 (2022).
Hoseinkhani, S., Tubino, R., Meinardi, F. & Monguzzi, A. Achieving the photon upconversion thermodynamic yield upper limit by sensitized triplet–triplet annihilation. Phys. Chem. Chem. Phys. 17, 4020–4024 (2015).
Cheng, Y. et al. Kinetic analysis of photochemical upconversion by triplet–triplet annihilation: beyond any spin statistical limit. J. Phys. Chem. Lett. 1, 1795–1799 (2010).
Cheng, Y. et al. On the efficiency limit of triplet–triplet annihilation for photochemical upconversion. Phys. Chem. Chem. Phys. 12, 66–71 (2010).
Ronchi, A. & Monguzzi, A. Developing solid-state photon upconverters based on sensitized triplet–triplet annihilation. J. Appl. Phys. 129, 050901 (2021).
Bi, P. et al. Donor-acceptor bulk-heterojunction sensitizer for efficient solid-state infrared-to-visible photon up-conversion. Nat. Commun. 15, 5719 (2024).
Collins, A. R., Zhang, B., Bennison, M. J. & Evans, R. C. Ambient solid-state triplet–triplet annihilation upconversion in ureasil organic–inorganic hybrid hosts. J. Mater. Chem. C 12, 6310–6318 (2024).
Naimovicius, L., Wołek, L., Zhang, S. & Pun, A. Activating solid-state triplet–triplet annihilation upconversion via bulky annihilators. J. Am. Chem. Soc. 148, 3811–3819 (2026).
Hu, X. et al. Sensitized triplet–triplet annihilation in nanostructured polymeric scintillators allows for pulse shape discrimination. Adv. Mater. 36, 2400443 (2024).
Gray, V., Moth-Poulsen, K., Albinsson, B. & Abrahamsson, M. Towards efficient solid-state triplet–triplet annihilation based photon upconversion: supramolecular, macromolecular and self-assembled systems. Coord. Chem. Rev. 362, 54–71 (2018).
Alves, J., Feng, J., Nienhaus, L. & Schmidt, T. W. Challenges, progress and prospects in solid state triplet fusion upconversion. J. Mater. Chem. C 10, 7783–7798 (2022).
Enomoto, R. et al. van der Waals solid solution crystals for highly efficient in-air photon upconversion under subsolar irradiance. Mater. Horiz. 8, 3449–3456 (2021).
Izawa, S. & Hiramoto, M. Efficient solid-state photon upconversion enabled by triplet formation at an organic semiconductor interface. Nat. Photon. 15, 895–900 (2021).
Geva, N. et al. A heterogeneous kinetics model for triplet exciton transfer in solid state u+pconversion. J. Phys. Chem. Lett. 10, 3147–3152 (2019).
Wieghold, S. et al. Triplet sensitization by lead halide perovskite thin films for efficient solid-state photon upconversion at subsolar fluxes. Matter 1, 705–709 (2019).
VanOrman, Z. A. & Nienhaus, L. Bulk metal halide perovskites as triplet sensitizers: taking charge of upconversion. ACS Energy Lett. 6, 3686–3694 (2021).
Wu, M. et al. Solid-state infrared-to-visible upconversion sensitized by colloidal nanocrystals. Nat. Photon. 10, 31–34 (2016).
Ogawa, T. et al. Donor–acceptor–collector ternary crystalline films for efficient solid-state photon upconversion. J. Am. Chem. Soc. 140, 8788–8796 (2018).
Williams, A. K. et al. Thiol–ene click chemistry: a modular approach to solid-state triplet–triplet annihilation upconversion. J. Mater. Chem. C 6, 3876–3881 (2018).
Lin, T.-A., Perkinson, C. F. & Baldo, M. A. Strategies for high-performance solid state triplet–triplet-annihilation-based photon upconversion. Adv. Mater. 32, 1908175 (2020).
Saenz, F. et al. Nanostructured polymers enable stable and efficient low-power photon upconversion. Adv. Funct. Mater. 31, 2004495 (2021).
Kamada, K. et al. Efficient triplet–triplet annihilation upconversion in binary crystalline solids fabricated via solution casting and operated in air. Mater. Horiz. 4, 83–87 (2017).
Ogawa, T., Yanai, N., Fujiwara, S., Nguyen, T.-Q. & Kimizuka, N. Aggregation-free sensitizer dispersion in rigid ionic crystals for efficient solid-state photon upconversion and demonstration of defect effects. J. Mater. Chem. C 6, 5609–5615 (2018).
Raišys, S., Juršenas, S. & Kazlauskas, K. Boost in solid-state photon upconversion efficiency through combined approach of melt-processing and purification. Solar RRL 6, 2100873 (2022).
Nienhaus, L. et al. Speed limit for triplet-exciton transfer in solid-state PbS nano3crystal-sensitized photon upconversion. ACS nano 11, 7848–7857 (2017).
Wieghold, S., Bieber, A. S., VanOrman, Z. A., Rodriguez, A. & Nienhaus, L. Is disorder beneficial in perovskite-sensitized solid-state upconversion? The role of DBP doping in rubrene. J. Phys. Chem. C 124, 18132–18140 (2020).
Islangulov, R. R., Lott, J., Weder, C. & Castellano, F. N. Noncoherent low-power upconversion in solid polymer films. J. Am. Chem. Soc. 129, 12652–12653 (2007).
Ishwara, T. et al. Nanoporous solid-state sensitization of triplet fusion upconversion. ACS Ener. Lett. 8, 4078–4084 (2023).
Jankus, V. et al. Energy upconversion via triplet fusion in super yellow PPV films doped with palladium tetraphenyltetrabenzoporphyrin: a comprehensive investigation of exciton dynamics. Adv. Funct. Mater. 23, 384–393 (2013).
Gholizadeh, E. M., Frazer, L., MacQueen, R. W., Gallaher, J. K. & Schmidt, T. W. Photochemical upconversion is suppressed by high concentrations of molecular sensitizers. Phys. Chem. Chem. Phys. 20, 19500–19506 (2018).
Hu, X. et al. Confinement-enhanced multi-wavelength photon upconversion based on triplet–triplet annihilation in nanostructured glassy polymers. Adv. Sci. 12, 2415160 (2025).
Dexter, D. L. A theory of sensitized luminescence in solids. J. Chem. Phys. 21, 836–850 (1953).
Förster, T. Zwischenmolekulare Energiewanderung und Fluoreszenz. Ann. Phys. 437, 55–75 (1948).
Yu, G., Gao, J., Hummelen, J. C., Wudl, F. & Heeger, A. J. Polymer photovoltaic cells: enhanced efficiencies via a network of internal donor–acceptor heterojunctions. Science 270, 1789–1791 (1995).
Narayanan, P. et al. Alleviating parasitic back energy transfer enhances thin film upconversion. Adv. Opt. Mater. 13, 2500252 (2025).
Zhang, Y. & Forrest, S. R. Triplets contribute to both an increase and loss in fluorescent yield in organic light emitting diodes. Phys. Rev. Lett. 108, 267404 (2012).
Bossanyi, D. G. et al. In optimized rubrene-based nanoparticle blends for photon upconversion, singlet energy collection outcompetes triplet-pair separation, not singlet fission. J. Mater. Chem. C 10, 4684–4696 (2022).
de Clercq, D. M. et al. Singlet fission in TIPS-anthracene thin films. Chem. Sci. 15, 6402–6409 (2024).
Pun, J. K. H. et al. TIPS-anthracene: a singlet fission or triplet fusion material? J. Photonics Energy 8, 022006 (2018).
Hestand, N. J. & Spano, F. C. Expanded theory of H- and J-molecular aggregates: the effects of vibronic coupling and intermolecular charge transfer. Chem. Rev. 118, 7069–7163 (2018).
Schulze, T. F. et al. Photochemical upconversion enhanced solar cells: effect of a back reflector. Aust. J. Chem. 65, 480–485 (2012).
Johnson, R., Merrifield, R., Avakian, P. & Flippen, R. Effects of magnetic fields on the mutual annihilation of triplet excitons in molecular crystals. Phys. Rev. Lett. 19, 285–287 (1967).
Johnson, R. & Merrifield, R. Effects of magnetic fields on the mutual annihilation of triplet excitons in anthracene crystals. Phys. Rev. B 1, 896–902 (1970).
Merrifield, R. Theory of magnetic field effects on the mutual annihilation of triplet excitons. J. Chem. Phys. 48, 4318–4319 (1968).
Forecast, R., Campaioli, F. & Cole, J. H. Magnetic field effects in triplet–triplet annihilation upconversion: revisiting Atkins and Evans’ theory. J. Chem. Theo. Comput. 19, 7816–7824 (2023).
Forecast, R. et al. Power dependence of the magnetic field effect on triplet fusion: a quantitative model. J. Phys. Chem. Lett. 14, 4742–4747 (2023).
Feng, J. et al. Magnetic fields reveal signatures of triplet-pair multi-exciton photoluminescence in singlet fission. Nat. Chem. 16, 1861–1867 (2024).
Meroni, D., Monguzzi, A. & Meinardi, F. Photon upconversion in multicomponent systems: role of back energy transfer. J. Chem. Phys. 153, 114302 (2020).
Gholizadeh, E. M. et al. Photochemical upconversion of near-infrared light from below the silicon bandgap. Nat. Photon. 14, 585–590 (2020).
Firdaus, Y. et al. Long-range exciton diffusion in molecular non-fullerene acceptors. Nat. Commun. 11, 5220 (2020).
Zhou, Y., Castellano, F. N., Schmidt, T. W. & Hanson, K. On the quantum yield of photon upconversion via triplet–triplet annihilation. ACS Energy Lett. 5, 2322–2326 (2020).
Birks, J. B., Dyson, D. J., Munro, I. H. & Flowers, B. H. Excimer fluorescence II. Lifetime studies of pyrene solutions. Proc. R. Soc. Lond. A 275, 575–588 (1963).
Katoh, R., Suzuki, K., Furube, A., Kotani, M. & Tokumaru, K. Fluorescence quantum yield of aromatic hydrocarbon crystals. J. Phys. Chem. C 113, 2961–2965 (2009).
Huang, Z. et al. Hybrid molecule–nanocrystal photon upconversion across the visible and near-infrared. Nano Lett. 15, 5552–5557 (2015).
Mongin, C., Garakyaraghi, S., Razgoniaeva, N., Zamkov, M. & Castellano, F. N. Direct observation of triplet energy transfer from semiconductor nanocrystals. Science 351, 369–372 (2016).
Kozlov, D. V. & Castellano, F. N. Anti-Stokes delayed fluorescence from metal–organic bichromophores. Chem. Commun. 2860–2861 (2004).
Kumarasamy, E. et al. Properties of poly- and oligopentacenes synthesized from modular building blocks. Macromolecules 49, 1279–1285 (2016).
Ishwara, T. et al. Raw spectroscopic data for “Structural exciton localization drives efficient solid-state sensitized triplet fusion upconversion.” figshare https://doi.org/10.6084/m9.figshare.30899465 (2026).