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Page 2 of 19 Lee et al. Microstructures 2023;3:2023021 https://dx.doi.org/10.20517/microstructures.2023.08

materials will experience the quantum confinement effect. This phenomenon relates to the exciton and
electronic energy level, which is continuous in bulk but becomes discrete in nanocrystals as the electron
movement is confined to a specific energy level. An exciton is a bound state between an electron hole in
valence band (VB) and an electron through Coulomb interaction. When a photon interacts with a
semiconductor material and the energy of the photon exceeds or equals the bandgap (Eg), an electron in the
VB is excited to the conduction band (CB), resulting in the formation of a positively charged hole referred
to as an electron hole. As the excited electron and electron hole are confined within a limited space, more
energy is required to excite them, which results in size-dependent band gaps and light emission. When a
material is confined in one dimension, it forms a quantum well structure. Similarly, two-dimensional
confinement results in a quantum wire, while three-dimensional confinement leads to a quantum dot,
[1-8]
which is a material that is confined in all three dimensions . This energy state results in unique
characteristics, including long fluorescence lifetime, narrow and symmetrical photoluminescence emission,
wide absorption, and high photoluminescence quantum yield (PLQY). Furthermore, the
photoluminescence emission band gap can be tuned by varying the size of QDs. Traditionally, combinations
of 0D core-shell structure materials and group 12-16 elements have been investigated as promising
quantum dot materials, such as ZnSe, ZnO, InP, InAs, and CdSe [9-11] . Recently, organic-inorganic metal
halide perovskites have been noticed as promising QD materials due to the recent successful development
of photovoltaic (PV) cells, LEDs, and sensors based on perovskite QDs [12-17] . However, in light of increasing
concerns about the potential toxicity of some materials, there is growing interest in developing alternatives
that are more biocompatible and environmentally friendly. For instance, carbon quantum dots (CQDs) and
graphene quantum dots (GQDs) are emerging as promising candidates [18-20] . Graphene Quantum Dots
(GQDs) exhibit remarkable size-dependent luminescence properties that are attributed to their quantum
confinement and edge effects. These properties make GQDs highly attractive for optoelectronic and
photodetector applications, including LEDs and electroluminescent devices. However, GQDs often suffer
from reduced fluorescence, which hampers their ability to function as optoelectronic devices due to phase
separation and agglomeration in organic or inorganic solvents. Furthermore, the non-stoichiometric nature
of GQDs makes it particularly challenging to achieve precise control over their chemical structure, size,
shape, and structural defects, which are directly related to their optoelectronic properties. Therefore, there
have been numerous attempts to incorporate GQDs into matrices such as polymer films or mesoporous
solids in order to control the size of the nanoparticles and stabilise them. However, since many of the
current fabrication methods are complicated and difficult to control, there is a need to investigate more
reproducible and simpler methods to fully utilise the great fluorescence properties of GQDs [21-25] .

Despite the promising potential of quantum dots (QDs) in various applications and the significant progress
achieved in material sciences, several challenges continue to hinder their widespread implementation. These
challenges include issues such as agglomeration, precise size control, and operational stability, which
demand further research and development to mitigate effectively. Generally, QDs show a strong tendency to
aggregate into larger particles due to their high surface energy, which leads to the loss of their unique
characteristics. Several recent studies have tried to mitigate the limitations of QDs through solvent
engineering, surface passivation using semiconducting film, encapsulation with polymers, or embedment of
QDs within porous nanomaterials [26-29] . However, most of these strategies require complex fabrication
processes, and it remains difficult to control the outcomes, which may reduce the efficacy of these methods.

Traditional nanomaterials with microporosity, such as mesoporous silica, zeolites, and porous carbon, have
been investigated for various applications, including drug delivery, biosensing, separation, and catalysts [30,31] .
Despite their great advantages, i.e., high surface area, tunable porosity, and biocompatibility, they tend to
have limited chemical tunability. This limitation inspired scientists to develop microporous functional