Is There Real Upconversion Photoluminescence from Graphene Quantum Dots?

Upconversion photoluminescence (PL) from graphene quantum dots (GQDs) excited by a xenon lamp is artificial. It is essentially excited by the second-order diffraction light of wavelength λ/2 co-existing in the red light. Real upconversion PL from GQDs is observed under excitation with a femtosecond pulsed laser, implying that coherent photons with high enough power density can be upconverted into blue light via GQDs. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.