In this paper, high-quality CdSe colloidal nanocrystals were synthesized by an improved Sol−Gel green technique. These colloidal nanocrystals were characterized by different techniques: Transmission Electron Microscopy (TEM) showed that the diameter of colloidal nanocrystals is about 3 nm; X-ray diffraction (XRD) demonstrated that CdSe colloidal nanocrystals formed in cubic phase; Fourier Transform Infrared spectroscopy (FT-IR) was employed to study the chemical compounds of asprepared sol; UV−visible absorption spectroscopy was used to evaluate optical properties of prepared CdSe colloidal nanocrystals, which indicated that the absorption peak is around 500 nm; Photoluminescence (PL) spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 50.2% with 440 nm excitation wavelengths. Experimental observation has shown that highly stable CdSe colloidal nanocrystals with a strong green emission were synthesized. The mentioned optical properties have not been reported before.

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The present paper investigates the linear and nonlinear optical properties of CdSe colloidal nanocrystals which have been prepared by an improved sol-gel green technique. UV-visible absorption spectroscopy and Z-scan technique were used to identify the linear and nonlinear optical properties of CdSe colloidal nanocrystals. The maximum peaks absorption for two samples 2.5 nm and 3 nm were 480 nm and 485 nm, respectively. In addition, the linear absorption coefficients (α), the nonlinear absorption coefficients (β), and the nonlinear refractive index (n2), with their signs and magnitudes for two different sizes of CdSe quantum dots (QDs) were obtained in 15, 25, and 50 mW laser intensities using the single beam Z-scan method by a continuous wave He-Ne laser at 632.8 nm wavelength. Finally, the photostability and chemical stability of the CdSe QDs were studied that have shown high stability of CdSe colloidal nanocrystals. The mentioned nonlinear optical properties have not been reported before.