Excited State Absorption Upconversion Induced by Structural Defects for Photocatalysis with a Breakthrough Efficiency

In the past decade, great progresses have been gained for up-conversion materials. However, there are still shortcomings in quantum efficiency, excitation and emission ranges and the cost of the materials. Herein, a new excited state absorption (ESA) up-conversion mode is discovered, which is directly induced by structural defects, showing distinct chemical characteristics from those based on lanthanide ions and triplet states chromophores. As a proof-of-concept model, the abundant N2C vacancies in graphitic carbon nitride nanosheets work as the crucial intermediate excitation states, which lead to graphitic carbon nitride up-conversely emitting the light at the wavelength of 436 nm excited by the light with the wavelength larger than 800 nm. This process is proven to proceed via a two-photon involved ESA mode with a breakthrough quantum efficiency of 0.64%. Moreover, compared with most classic up-conversion materials, graphitic carbon nitride features easy preparation, low cost and low toxicity. Further, we combine N2C vacancies enriched graphitic carbon nitride with the state-of-the-art photocatalysts such as In2S3 and CdS, and successfully achieved an infrared light driven photocatalytic reactions. These findings offered a new family of up-conversion materials; more semiconductors with various structural defects are potential complementary members.