The Next Stage in Colloidal Synthesis of Aqueous CdSe Quantum Dots: High Throughput and Intense Emissive Properties

Abstract

Quantum dots (QDs) of CdSe have been produced with high yield using common reagents in water at 150 °C. The QDs thus produced are water compatible, show intense fluorescence emission and have high quantum yields (QYs). Their size can be controlled similarly to the high temperature organometallic method of synthesizing QDs, and these QDs produced in organic solvents at high temperature and the QDs produced in water both show comparable QYs. The great advantage is that a green solvent, water, is used and their separation from the water is very simple. They can be stored dry very easily. Similar to the organic method their size can be controlled by time, producing QDs with distinct fluorescence. The size obtained by TEM for 30, 60 and 90 minutes of reaction is 4.18 nm, 6.7 nm and 8.6 nm, respectively. This parallels the change in the emission wavelength of the QDs produced; green, yellow and orange, respectively. TEM dimensions are very similar to these of DLS (dynamic light scattering). These QDs display the hexagonal wurtzite phase, common for the higher temperature synthesis of QDs in organic solvents, and not the zinc blende phase of CdSe QDs common for the lower temperature water synthesis of QDs. The prepared QDs have shown the same intense emission for over a year after being synthesized.

Solvent Effects on Fluorescence Properties of Carbon Dots: Implications for Multicolor Imaging

“…10,11 They are expected to replace the traditional semiconductor quantum dots with biological toxicity and environmental hazards, especially CdSe quantum dots owing to a high fluorescence quantum yield. 12 According to the rule of Kasha, the fluorescence emission wavelength of organic dyes and semiconductor quantum dots remains unchanged with the excitation wavelength 13 since the photons are emitted rapidly from the ground-state energy level to the lowest excited-state energy level. The organic dyes hold a narrow excitation wavelength and instability of emission.…”

“…According to their structure, CDs consist of carbon nanodots (CNDs), , graphene quantum dots (GQDs), , and polymer dots (PDs). , CDs are environmentally friendly and low-toxic fluorescent nanomaterials. CDs also possess good biocompatibilities and excellent optical properties, , which are applied for sensing and bioimaging. , They are expected to replace the traditional semiconductor quantum dots with biological toxicity and environmental hazards, especially CdSe quantum dots owing to a high fluorescence quantum yield …”