I have a carbon dot (C) which I reduced it by NaBH4 (rC). Further infor both C and rC the emission wavelength is similar i.e. 440 nm however change in excitation wavelngth was observed i.e. C exhibit the excitation peak at 380nm, and the excitation peak of rC is blue-shifted by 20nm at 360nm. Also the band gap of C and rC are 2.1 and 2.78 eV respectively. Please explain the possible reason for the blue shift of the excitation spectrum with reduction.
Dear Pranav,
The answer is basically within your question. Band gap in inversely proportional to absorbance wavelength. As, the band gap is increased with reduction, the absorbance peak (often a hump/ Shoulder like band for Carbon dots) of rC also decreased. Hence, the excitation wavelength for maximum emission is blue-shifted.
I think, you have measured the UV-Vis absorption spectra for C and rC.
Dear Pranav,
Yes @Saptarshi Mandal is right, the observed blue shift in the excitation wavelength is directly related to energy bandgap increase whith the reduction of the samples and the underlying effect is a decrease of Urbach tail as a result of disorder decrease (samples more homogeneous as a result of reduction) or defect neutralization by reduction reaction.
You are most welcome.
Here is an interesting reference related to your question:
''Enhancing the luminescence of carbon nanodots in films by tailoring the functional groups through alkylamine-functionalization and reduction''
By Minsu Kim, Phil Woong Kang, Sunjoong Park, Duk Young Jeon and Hyunjoo Lee
In Journal Physical Chemistry Chemical Physics Issue 47, 2019
https://doi.org/10.1039/C9CP05241K
I have comprehensively investigated the bandgap effect on optical properties of CDs :
Article Two-Photon Dual-Emissive Carbon Dot-Based Probe: Deep Tissue...
Hope it helps.
Cheers,
Pooria
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