Origin of Photoluminescence in Carbon Quantum Dots (CQDs)

Hernanie, Jr. Salazar^1*, Kuong-Ngai Ng¹, Xuan-Dung Mai², Che-Yu Chang¹, Arvin Lester C. Jusi¹, Der-Jun Jang¹

¹Department of Physics, National Sun Yat-sen University, Kaohsiung city, Taiwan
²Department of Chemistry, Hanoi Pedagogical University 2, Vinh Phuc, Viet Nam

* Presenter:Hernanie, Jr. Salazar, email:h-salazar@g-mail.nsysu.edu.tw

Temperature-dependent photoluminescence (PL) and time-resolved PL (TRPL) of carbon quantum dots (CQDs) were measured to investigate the possible source of luminescence in the material. XPS measurements revealed an increasing density of nitrogen-related functional groups as the density of the deposit increases. PL and UV-vis absorption show that the absorbance and emission of the samples are directly related to the density/thickness of the deposit. The large Stoke’s shift in the absorption and emission spectra indicates the presence of vibrational relaxation in CQD films. 0-0 transition peak was observed to blueshift with a faster decay time as temperature increases. This temperature-dependent blueshift and lifetimes in the films possibly indicate the presence of thermally activated hopping sites which is also seen in carbon-based organic semiconductors. These hopping sites are related to nitrogen-based functional groups as also suggested by our XPS measurements.

Keywords: photoluminescence, carbon, quantum dots, time-resolved, spectroscopy