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Identifying Clusters and/or Small-Size Quantum Dots in Colloidal CdSe Ensembles with Optical Spectroscopy
Lijia Li1, Meng Zhang2, Nelson Rowell3
1Engineering Research Center in Biomaterials , Sichuan University , Chengdu , Sichuan 610065 , People's Republic of China.
The Journal of Physical Chemistry Letters
|October 9, 2019
Summary
Photoluminescence excitation spectroscopy reveals that cadmium selenide quantum dot (QD) synthesis can produce clusters, not just QDs. This finding complicates accurate size determination of small semiconductor quantum dots.
Area of Science:
- Materials Science
- Nanotechnology
- Physical Chemistry
Background:
- Optical absorption and photoluminescence (PL) are sensitive to the size and distribution of colloidal semiconductor quantum dots (QDs).
- Characterizing reaction products, especially clusters and small QDs, requires advanced spectroscopic techniques.
- Photoluminescence excitation (PLE) spectroscopy offers deeper insights into the nature of synthesized nanomaterials.
Purpose of the Study:
- To investigate the presence and nature of clusters versus small quantum dots in synthesized cadmium selenide (CdSe) materials.
- To evaluate the utility of photoluminescence excitation (PLE) spectroscopy in distinguishing between clusters and QDs.
- To understand how reaction conditions influence the formation of different nanoscale species.
Main Methods:
- Two non-hot-injection synthesis routes for CdSe were employed using cadmium oleate (Cd(OA)2) and selenium (Se) in 1-octadecene (ODE).
- Sequential extraction of reaction products was performed.
- Optical absorption, photoluminescence (PL), and photoluminescence excitation (PLE) spectroscopies were utilized to analyze the synthesized materials.
Main Results:
- Both synthesis methods yielded products with apparent red shifts in absorption and PL (fwhm ~30 nm).
- The reaction involving diphenyl phosphine (HPPh2) produced an ensemble containing multiple types of clusters with distinct optical properties.
- The reaction without HPPh2 primarily yielded small-size CdSe quantum dots.
- Evidence suggests the co-existence of clusters within small-size CdSe QD products.
Conclusions:
- Photoluminescence excitation (PLE) spectroscopy is crucial for accurately characterizing reaction products, including clusters and small quantum dots.
- The presence of clusters in synthesized CdSe materials complicates precise size determination of quantum dots.
- Reaction conditions, such as the presence of additives like HPPh2, significantly impact the nature of the synthesized nanoscale products.
