Temperature-Dependent Excitonic Photoluminescence and Nonlinear Absorption of CdTe Nanocrystal/Polyvinyl Alcohol Films

The temperature dependence of the excitonic photoluminescence (PL) and nonlinear absorption characteristics of CdTe nanocrystals (NCs)/polyvinyl alcohol (PVA) film are investigated using steady-state/time-resolved PL spectroscopy and Z-scan methods. The excitonic PL peaks of CdTe NCs can be observed at the wavelengths from 560 to 670 nm, with size changes from 2.1 to 3.9 nm. From the temperature-dependent PL spectra, the smaller photon energy of the PL emission peak, the rapidly decreasing PL intensity, and the wider linewidth are observed with increasing temperature from 80 to 300 K. It is revealed that the exciton PL is composed of both trapped state and band-edge excitonic state, which presents biexponential fitting dynamics. The short-lived species is due to the surface-trapped state recombination in NCs, which has a photogenerated trapped channel and a time-resolved peak shift. The species with a long-lived lifetime is ascribed to the intrinsic excitonic recombination. Through the femtosecond Z-scan method, the nonlinear absorption coefficient becomes smaller with the increase in the size of the NCs. The optical properties of the CdTe NC/PVA film show the potential of II-VI traditional NCs as display and luminescent materials that can utilize the combination of exciton PL and nonlinear absorption for expanded functionality.

Synthesis of Magnetic Ions-Doped QDs Synthesized via a Facial Aqueous Solution Method for Optical/MR Dual-Modality Imaging Applications

This research reports the preparation and examination of Cadmium Telluride (CdTe) Quantum Dots and doping CdTe QDs with Europium (Eu), Gadolinium (Gd), and Manganese (Mn) prepared in aqueous solution using TGA as a capping agent. Magnetic QDs (MQDs) are important agents for fluorescence (FL) /magnetic resonance (MR) dual-modal imaging due to their excellent optical and magnetic properties. Herein, the chemical bonds, structural, fluorescence, and magnetized properties of CdTe QDs and effect of Mn, Eu, and Gd ions doping on their properties were examined by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTM), Energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL), Ultraviolet-visible spectroscopy (UV-Vis), and vibrating sample magnetometer measurements (VSM). Almost similar X-Ray patterns with the absence/presence of ions for all samples with cubic crystal structures were obtained which indicates that the introduction of ions into CdTe QDs could not alteration the cubic primary structure of CdTe. Monodisperse size distribution with seemingly-spherical shapes, and also, the estimated mean diameters about 3 and less than 3 nm of QDs Were obtained. The effect of X ions injection on the fluorescence and UV-Vis properties of the QDs were also investigated. Optical studies showed the decreases in bandgap with the heating time increases during synthesis, and they undergo red-shift. The CdTe nanocrystals with high PL quantum yields were achieved in more than 6 h of heating. Also, investigations have shown the quenching of fluorescence by the existence of ions in the CdTe QDs. And Also, all the ions doped QDs exhibited ferromagnetic behavior at room temperature by a vibrating sample magnetometer which confirmed the success of the presentation of ions into CdTe cubic crystal structure. They can have been employed as a suitable contrast agent successfully for biological applications such as FL/MR dual-modal imaging.

Synthesis and characterization of oleic acid stabilized CdTe quantum dots and their properties as luminescence quencher of a pyridine pendented rod-coil homopolymer

We report a facile one-step non aqueous synthesis of oleic acid stabilized cadmium telluride (CdTe) quantum dots (QDs) with an average diameter of 3 nm to 4 nm by hot injection method. The synthesized oleic acid capped QDs observed by TEM were nearly spherical. The optical properties of QDs were characterized by UV-Vis absorption spectra and photoluminescence (PL) spectra. The structures of QDs and their surface passivation were further verified using transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The quenching effect of the CdTe QD was explored by addition of CdTe nanocrystals into a solution of rod-coil homopolymer (poly[10-(6-(9,9-diethyl-7-(pyridin-4-yl)-9H-fluoren-2-yl)naphthalen-2-yloxy) decyl methacrylate]) (PFNA) having pendent pyridine. The gradual addition of quantum dots to the solution of PFNA quenched the PL spectra of PFNA. This may be used to explore the coordination ability of pyridine containing homopolymer with CdTe quantum dots.