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

Area of Science:

• Materials Science
• Photochemistry
• Nanotechnology

Background:

• Upconversion materials are crucial for converting lower-energy light to higher-energy photons.
• Existing upconversion methods often rely on lanthanide ions or triplet-state chromophores, limiting their chemical stability and applicability.
• Structural defects in semiconductors can significantly influence their optoelectronic properties.

Purpose of the Study:

• To prepare nitrogen-deficient graphitic carbon nitride (g-C3N4) with controllable structural defects.
• To discover and characterize a novel upconversion mechanism in g-C3N4.
• To demonstrate the application of this new upconversion material in infrared light-driven photocatalysis.

Main Methods:

• Synthesis of nitrogen-deficient g-C3N4 nanosheets.
• Characterization of structural defects, specifically N2C vacancies.
• Spectroscopic analysis to identify the upconversion mechanism (excited state absorption - ESA).
• Photocatalytic experiments using visible and infrared light.

Main Results:

• A new ESA upconversion mode was discovered in nitrogen-deficient g-C3N4, directly induced by N2C vacancies.
• The material exhibited upconverted emission at 436 nm upon excitation with 800 nm light.
• A breakthrough quantum efficiency of 0.64% was achieved for the two-photon ESA process.
• g-C3N4 combined with In2S3 and CdS demonstrated efficient infrared light-driven photocatalytic reactions.

Conclusions:

• Nitrogen-deficient g-C3N4 presents a new class of defect-engineered upconversion materials.
• The discovered ESA upconversion mechanism offers distinct advantages over traditional methods.
• These findings pave the way for developing novel semiconductor photocatalysts driven by infrared light.