Chapter 3: Excitation wavelength-dependent spectral shift and large exciton binding
3.4. Conclusion
excitation. The WS2 QDs exhibit characteristic bright green emission, as evident from Fig. 3.8(a).
On the other hand, the fluorescence images distinctively depict a gradual reduction in the fluorescence background with an increase in the concentration of SWCNT1 (Fig. 3.8(b-d)). This gives us direct evidence of the systematic quenching of fluorescence of the as-prepared WS2 QD with the increase in the concentration of SWCNT1.
Based on our observations, we propose that during the ultrasonication process, the WS2
QDs form complexes with SWCNT. The presence of ample surface edge sites/defects on the WS2
QDs allow their attachment to the abundant defect sites on the carbon nanotube walls, which lead to the formation of non-fluorescent ground state complexes, primarily responsible for effective quenching of fluorescence13, 42. This attachment of WS2 QDs on walls of the SWCNT, in turn, leads to charge transfer and further quenching of the PL intensity of the WS2 QDs.
79 | S p e c t r a l a n a l y s i s o f W S2 Q D s a n d i n t e r a c t i o n w i t h S W C N T s
transfer from WS2 QDs to the SWCNTs due to the strong bonding between them. The quenching efficiency is shown to be higher for more defective SWCNT1 than that of less defective SWCNT2.
The results are insightful in understanding the interaction between WS2 QD and SWCNTs and regulating the fluorescence intensity of WS2 QDs, which is important for various applications in biomedical areas, such as bio-imaging/sensing, drug delivery, etc.
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