Carbon dots (CDs) have been widely studied as an alternative to quantum dots, semiconductors, and rare-earth-element-doped structures, as they are non-toxic and metal-free optical materials [1,2]. In medicine, they might be used, for example, in drug delivery, diagnostic, and sensing [3].
CDs were synthesized using low-temperature ammonium citrate pyrolysis, and their structure (XRD, TEM, FT-IR) and optical properties were analyzed. The TEM analysis showed that blue-emitting carbon dots (bCDs) have spherical shapes with a 4-7 nm diameter, and green-emitting CDs (gCDs) have the shape of rods with a length of 20-50 nm. The sol–gel method was used to synthesize silica and silica–calcia monoliths with embedded CDs. The aim of the experiment was to obtain composites in which the luminescence of the CDs could be observed and further used to monitor different biological processes. For that reason, glasses with different concentrations of CDs (0.03-0.2 wt.%) were prepared, and optical properties (absorption, excitation, and emission) were measured. It was found that the addition of urea during the synthesis of CDs led to a change in the emission color of the CDs from blue (λem: 450 nm) to green (λem: 540 nm). Comparing the emission spectra of the CDs, colloids, and composites, changes in the maximum emission and its intensity were observed. The emission intensity of CDs is lower in glass structures, and the maximum emission shows a red shift in glass composites. Spectroscopic measurements showed that the luminescence intensity and emission maximum depend on the excitation wavelength.
Acknowledgment
This work was supported by the National Centre for Research and Development research grant No. LIDER/26/0121/L-12/20/NCBR/2021
References
[1] Zhang W. et al., RSC Adv., 2017, 7, 20345-20353
[2] Qu D. et al., Scientific Reports, 2014, 4, 5294
[3] Kaurav H. et al., Frontiers in Chemistry, 2023; 11, 1227843
