Laser Wavelength dependence of nonlinear optical properties of CdTe, CdS, and core-shell CdTe/CdS QD nanoparticles

In this paper, CdTe, CdS, and CdTe/CdS core-shell nanoparticles were synthesized using photochemical methods, and their structural and optical properties were examined using techniques such as X-ray diffraction spectroscopy (XRD), Scanning Electron Microscopy (SEM), UV-Vis absorption and Photoluminescence (PL) spectroscopy. The results showed that the synthesized nanoparticles CdTe, CdS, and CdTe/CdS with optical bandgaps of 2.32, 2.37, and 2.15 eV, and 3, 2.8, and 8 nm average sizes. respectively have uniform sizes and distributions, beyond that their optical properties are highly dependent on their size and chemical composition. Afterward, using the Z-scan technique, nanoparticles nonlinear absorption (NLA) and nonlinear refraction (NLR) coefficients were evaluated under CW laser Diode (532 nm), He-Ne (632.8 nm), and Nd:YAG pulsed laser with wavelength and pulse width (1064 nm, 3 ns) and its second harmonic (SHG) (532 nm). According to the experimental results, CdTe, CdS, and CdTe/CdS nanoparticles have shown unique NLA and NLR behaviors and strike optical limiting due to strong dependency on laser wavelengths. For 532 nm diode laser (CdTe, CdS, and CdTe/CdS) QDs, the NLA and NLR coefficients and orders were calculated as (53.48, 27.94, 30.13) cm/MW and (6.496, -14.206, 9.21) cm²/GW, respectively. The results indicate that (NLA) β with single photon absorption (SPA) mechanism for CW diode laser (532 nm), two-photon absorption (TPA) for 632.8 nm, and reverse saturable absorption (RSA) for 1064 nm IR/SHG lasers, and in the case of (NLR), the self-focusing and defocusing mechanisms have been observed and determined for each nanoparticle. These findings can serve as a basis for designing and developing advanced Photonic and optical and devices that utilize these nanoparticles.