2.1 Carbonaceous Quantum Dots
19
Polymer Passivation. Polymer passivation with surface emissive traps is usually
used to make the QY of GQDs and C-dots better. The most frequently used polymer
is polyethylene glycol (PEG), even though others have been reported as well such
as branched polyethyleneimine (BPEI) (Liu et al. 2007; Wang et al. 2013; Liu et al.
2012). A layer of PEG1500N can make the QY of C-dots more than 75%. In contrast
research, Shen et al. prepared bare GQDs and GQDs that were passivated with PEG.
The result indicated that the QY of the modified GQDs was one time higher than the
former (Dong et al. 2012b).
Surface passivation. Surface passivation makes the synthesis process complicated and the particle sizes increased whereby placing restrictions on applications.
When it comes to attaching Chemical Moieties, various chemical groups have been
adhered to GQDs and C-dots in the synthesis process or after synthesis such as
diamine thiol, alkylamine, and hydrazide (Shen et al. 2011). The electron-donating
groups often improve QY by avoiding non-radiative associativity and usually cause
evident wavelength shift. For instance, GQDs synthesized by green oxidation become
blue when substituting alkylamine for carboxyl. In Tetsuka et al.’s work, it was illustrated that the emission wavelength of GQDs might be widely adjusted (blue to
yellow) by regulating the degree of functionalization of amine (Zhu et al. 2012).
2.1.3.3 Heteroatom Doping
Heteroatom doping (by far the most common is, nitrogen doping) could be applied
to fine-tune or attain new PL and the other physicochemical performance of C-dots
and GQDs (Tetsuka et al. 2012; Luo et al. 2013). Heteroatoms could be retained
from precursors in the process of synthesis. Wei et al. used the Maillard reaction
between glucose and amino acids for the sake of the systematic preparation of a train
of N-doped C-dots accompanied with high QY (about 69.1%) and PL tuned through
N-doping level (shorter emission wavelength along with greater N-doping through
basic amino acids) (Wang et al. 2014b). In addition, it has been clearly observed
that N-doping (principally pyrrolic, potentially pyridinic, but not graphitic doping
configuration) on GQDs enhances QY and leads to blue shift in emission because of
the electron-withdrawing capability of nitrogen atoms. A number of researches also
present that N-doping has the ability to provide up-conversion property for GQDs
(Wei et al. 2014). Some other elements [e.g., Si, (Li et al. 2012b) P, (Qian et al. 2014)
S, (Prasad et al. 2013; Kwon et al. 2013) and B (Fan 2014)] have as well been doped
into C-dots and GQDs, in order to change PL properties or obtain greater catalytic
performance. S/N co-doped C-dots and GQDs are able to achieve QY as great as 73
and 71%, severally (Dong et al. 2013).
19
Polymer Passivation. Polymer passivation with surface emissive traps is usually
used to make the QY of GQDs and C-dots better. The most frequently used polymer
is polyethylene glycol (PEG), even though others have been reported as well such
as branched polyethyleneimine (BPEI) (Liu et al. 2007; Wang et al. 2013; Liu et al.
2012). A layer of PEG1500N can make the QY of C-dots more than 75%. In contrast
research, Shen et al. prepared bare GQDs and GQDs that were passivated with PEG.
The result indicated that the QY of the modified GQDs was one time higher than the
former (Dong et al. 2012b).
Surface passivation. Surface passivation makes the synthesis process complicated and the particle sizes increased whereby placing restrictions on applications.
When it comes to attaching Chemical Moieties, various chemical groups have been
adhered to GQDs and C-dots in the synthesis process or after synthesis such as
diamine thiol, alkylamine, and hydrazide (Shen et al. 2011). The electron-donating
groups often improve QY by avoiding non-radiative associativity and usually cause
evident wavelength shift. For instance, GQDs synthesized by green oxidation become
blue when substituting alkylamine for carboxyl. In Tetsuka et al.’s work, it was illustrated that the emission wavelength of GQDs might be widely adjusted (blue to
yellow) by regulating the degree of functionalization of amine (Zhu et al. 2012).
2.1.3.3 Heteroatom Doping
Heteroatom doping (by far the most common is, nitrogen doping) could be applied
to fine-tune or attain new PL and the other physicochemical performance of C-dots
and GQDs (Tetsuka et al. 2012; Luo et al. 2013). Heteroatoms could be retained
from precursors in the process of synthesis. Wei et al. used the Maillard reaction
between glucose and amino acids for the sake of the systematic preparation of a train
of N-doped C-dots accompanied with high QY (about 69.1%) and PL tuned through
N-doping level (shorter emission wavelength along with greater N-doping through
basic amino acids) (Wang et al. 2014b). In addition, it has been clearly observed
that N-doping (principally pyrrolic, potentially pyridinic, but not graphitic doping
configuration) on GQDs enhances QY and leads to blue shift in emission because of
the electron-withdrawing capability of nitrogen atoms. A number of researches also
present that N-doping has the ability to provide up-conversion property for GQDs
(Wei et al. 2014). Some other elements [e.g., Si, (Li et al. 2012b) P, (Qian et al. 2014)
S, (Prasad et al. 2013; Kwon et al. 2013) and B (Fan 2014)] have as well been doped
into C-dots and GQDs, in order to change PL properties or obtain greater catalytic
performance. S/N co-doped C-dots and GQDs are able to achieve QY as great as 73
and 71%, severally (Dong et al. 2013).