Thermal reduction effects on one- and two-photon luminescence in graphene quantum dots

• Thermal reduction affects GQD's size, crystallization and oxygen groups.
• Thermal treatment with higher temperature makes a blue-shift phenomenon in optical properties.
• Good two photon luminescence properties can be observed at low thermal temperatures.

Thermal reduced graphene quantum dots (GQDs) have been synthesized and investigated based on various heating temperatures. The characterizations of GQDs' size, crystallization and oxygen group confirm the thermal reduction influences. In experiment, GQD solutions display broad UV–vis absorption and good one-photon luminescence phenomena. Moreover, thermal treatment with higher temperature makes a blue-shift phenomenon in optical properties. Additionally, good two-photon luminescence properties can be observed with the treatment of lower thermal temperatures. First-principle calculations theoretically confirm that the sizes and oxygen groups can affect the band gaps and orbital's distributions. The observed good one- and two-photon luminescence properties can be potential for future bioimaging applications.

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