Real-time monitoring of CdTe quantum dots growth in aqueous solution

Abstract

Quantum dots (QDs) are remarkable semiconductor nanoparticles, whose optical properties are strongly size-dependent. Therefore, the real-time monitoring of crystal growth pathway during synthesis gives an excellent opportunity to a smart design of the QDs luminescence. In this work, we present a new approach for monitoring the formation of QDs in aqueous solution up to 90 °C, through in situ luminescence analysis, using CdTe as a model system. This technique allows a detailed examination of the evolution of their light emission. In contrast to in situ absorbance analysis, the in situ luminescence measurements in reflection geometry are particularly advantageous once they are not hindered by the concentration increase of the colloidal suspension. The synthesized particles were additionally characterized using X-ray diffraction analysis, transition electron microscopy, UV-Vis absorption and infrared spectroscopy. The infrared spectra showed that 3-mercaptopropionic acid (MPA)-based thiols are covalently bound on the surface of QDs and microscopy revealed the formation of CdS. Setting a total of 3 h of reaction time, for instance, the QDs synthesized at 70, 80 and 90 °C exhibit emission maxima centered at 550, 600 and 655 nm. The in situ monitoring approach opens doors for a more precise achievement of the desired emission wavelength of QDs.

Figure 1

in situ luminescence monitoring device (Lumibox) coupled to a fluorescence spectrometer.

Figure 2

(a) 3D spectra and (b) colormap profile of at 70, 80, and 90 °C as a function of reaction time.

Figure 3

(a) PL emission spectra and (b) maximum emission wavelength for CdTe quantum dots synthesized at 70, 80, and 90 °C, as a function of reaction time.

Figure 4

Chromaticity CIE 1931 diagram of CdTe quantum dots synthesized at (a) 70, (b) 80, and (c) 90 °C, as a function of time.

Figure 5

(a) Absorption spectra, (b) photo of the concentrated samples (in water) under 405 nm light. of CdTe quantum dots synthesized at 70, 80, and 90 °C.

Figure 6

Bandgap energy estimation via Tauc Plot of CdTe quantum dots synthesized at (a) 70, (b) 80, and (c) 90 °C.

Figure 7

Crystalline structure of CdTe quantum dots, showing a cubic crystalline phase, where cadmium is represented in blue and tellurium in red.

Figure 8

(a) FTIR spectra of CdTe quantum dots synthesized at 70, 80, and 90 °C and, (b) Comparison of CdTe QD prepared at 90 °C and pure MPA spectra.

Figure 9

(a) HRTEM images of QDs synthesized at 70 °C, (b) CdS nanoparticles, (c) CdTe nanoparticles and (d) CdS nanoparticles ED measurements.