  In this work, we have systematically investigated the structural, electronic,
vibrational and optical properties of the edge-functionalized hg-C3N4 quantum
dots with the aim of exploring their possible applications in solar cells and
other optoelectronic devices such as light-emitting diodes. The functional
groups considered in this work are methyl (-CH$_3$), fluorine (-F), and
oxygenated groups such as aldehyde (-CHO), carboxyl (-COOH), ketone
(-COCH$_3$), and hydroxyl (-OH) groups. The edge-functionalization resulted in
significant tuning of the electronic, vibrational, and optical properties.
Thus, their structural fingerprints are present in both their vibrational and
optical properties, thereby allowing their detection both in the Raman as well
as optical spectroscopies. It is observed that edge functionalization broadens
the energy range of optical absorption, leading to coverage of most of the
ultraviolet and visible regions. This implies that the edge-functionalization
of hg-C$_3$N$_4$ quantum dots can be used in a variety of optoelectronic
devices such as solar cells and light emitting diodes.
