Cadmium Octanoate Research Articles

Intensity-dependent optical nonlinearities of composite materials made of ionic liquid crystal glass and bimetallic nanoparticles

ABSTRACT Although isotropic glass materials are ubiquitous in everyday life, the properties and applications of anisotropic liquid crystal glasses stable at room temperature are still insufficiently explored. In this paper, nonlinear-optical properties of unconventional glass nanocomposites made of mesogenic cadmium octanoate and bimetallic nanoparticles are reported. Two types of bimetallic nanoparticles (Ag/Au core – Au shell and Ag/Au homogeneous alloy) are synthesised utilising an ionic liquid crystal phase of cadmium octanoate as a nanoreactor. A nonlinear-optical characterisation of the studied samples is performed by means of a Z-scan technique and using nanosecond laser pulses at 1064 nm excitation wavelength. The studied nanocomposites exhibit a strong nonlinear-optical response with the magnitude of the third-order nonlinear optical susceptibility within a 2.81 × 10−8 - 2.19 × 10−7 esu range. The measured values of the effective nonlinear refractive indices and nonlinear absorption coefficients depend on the laser beam intensity. The physical mechanisms of the observed intensity-dependent optical nonlinearities are discussed.

Colloidal Synthesis of Laterally Confined Blue-Emitting 3.5 Monolayer CdSe Nanoplatelets.

The typical synthesis protocol for blue-emitting CdSe nanoplatelets (NPLs) yields particles with extended lateral dimensions and large surface areas, resulting in NPLs with poor photoluminescence quantum efficiency. We have developed a synthesis protocol that achieves an improved control over the lateral size, by exploiting a series of long-chained carboxylate precursors that vary from cadmium octanoate (C8) to cadmium stearate (C18). The length of this metallic precursor is key to tune the width and aspect ratio of the final NPLs, and for the shorter chain lengths, the synthesis yield is improved. NPLs prepared with our procedure possess significantly enhanced photoluminescence quantum efficiencies, up to 30%. This is likely due to their reduced lateral dimensions, which also grant them good colloidal stability. As the NPL width can be tuned below the bulk exciton Bohr radius, the band edge blue-shifts, and we constructed a sizing curve relating the NPL absorption position and width. Further adjusting the synthesis protocol, we were able to obtain even thinner NPLs, emitting in the near-UV region, with a band-edge quantum efficiency of up to 11%. Results pave the way to stable and efficient light sources for applications such as blue and UV light-emitting devices and lasers.

Optical nonlinearity in nanocomposites based on metal alkanoates with hybrid metal/semiconductor and semiconductor/semiconductor nanoparticles

Spectral properties and the nonlinear optical response in nanocomposites of ionic liquid crystals (ILC) of cadmium octanoate containing hybrid core/shell nanoparticles (NPs) is studied. The hybrid NPs consist of either an Ag-core and a semiconductor-shell, or a semiconductor1-core and a semiconductor2-shell. Two-wave mixing with excitation by nanosecond pulses laser was used to observe the generation of high diffraction orders in the dynamic regime. The coefficients of optical nonlinear refraction were determined based on the measured diffraction efficiencies. Excitation of polaritons in the hybrid NPs and their electronic type of nonlinearity are responsible for the photoinduced nonlinear response in these nanocomposites.

Nonlinear optical properties of metal alkanoate composites with hybrid core/shell nanoparticles

New composites with hybrid CdSe/ZnS and Au/CdSe nanoparticles (NPs) were chemically synthesized in the thermotropic liquid crystalline phase (smectic A) of cadmium octanoate. Features of structure and nonlinear optical properties of glassy cadmium octanoate composites with hybrid core/shell NPs were studied using small-angle X-ray scattering method and Z-scan technique. Experimental optical setup (Z-scan) is based on a Nd: YAG laser, generating 9 ns pulses with a repetition rate of 0,5 Hz on a wavelength of 532 nm. The effects of the influence of hybrid NPs on the nonlinear optical properties of nanocomposites are considered in this study.

Intensity dependent nonlinear absorption coefficients and nonlinear refractive indices of glass-forming ionic liquid crystals doped with gold and silver nanoparticles

In this paper, we report nonlinear-optical properties of the newly designed glassy nanocomposites made of mesomorphic cadmium octanoate (CdC8) doped with a small fraction of gold (Au) and silver (Ag) nanoparticles (NP). The nanosecond laser scanning measurements (Z-scan) were performed at the wavelength (532nm) within the absorption band of the studied materials. Both types of nanocomposites (CdC8|Au NP and CdC8|Ag NP) exhibit strongly pronounced dependence of the nonlinear absorption coefficient and nonlinear refractive index on the intensity of the laser beam. Physical mechanisms leading to this dependence are discussed.

Photoconductivity of ionic thermotropic liquid crystal with semiconductor nanoparticles

The characteristics of photocurrent are investigated in new nanocomposites of cadmium octanoate with semiconductor nanoparticles (NPs) as well as in pure matrix of the cadmium octanoate. CdS NPs are synthesized inside the cadmium octanoate matrix during one-step chemical reaction. The photoconductivity in these nanocomposites has been detected in wide temperature range. The photocurrent exhibits nonlinear behavior over all different mesophases of the nanocomposites. Two types of near-electrode processes that occur depending on the value of applied voltage are considered to explain the nonlinear dependence of the current-voltage characteristics.

Luminescent microscopy of the small ensembles of the CdSe nanocrystalls synthesized in the liquid crystal matrix of the cadmium octanoate

Here we present investigation of the thin film with CdSe nanocrystals with the size 2.3 nm made from low-concentration toluene solution. Using fluorescent microscopy method we have found small nanocrystals ensembles up to single nanocrystals. Luminescence spectra in different parts of the test sample were registered. Analysing them we can draw a conclusion about the inhomogeneous nature of the luminescence spectra of the bulk nanocomposite material.

Influence of semiconductor and metal nanoparticles on the dielectric properties of ionic matrix cadmium octanoate.

Dielectric properties of ionic composites consisted of cadmium octanoate matrix and semiconductor or metal nanoparticles have been investigated. The nanoparticles of different nature (semiconductor CdS, metal Au, and metal core-semiconductor shell Au-CdS) were chemically synthesized in the smectic A phase of (Cd+2(C7H15COO)−2, CdC8) that was used as a nanoreactor. These nanocomposites are very stable and well ordered; the size and shape of the nanoparticles (NPs) are well controlled during the synthesis. The main aim of the research was to examine the influence of nanoparticles on the dielectric properties of ionic matrix, which has smectic A ordered structure. Electrical characteristics were investigated at different temperatures, which correspond to different phases of the material. The conductivity of nanocomposites has an activation nature. The electrical conductivity anisotropy confirms the structural anisotropy of the nanocomposites. The conductivity of the nanocomposite along the cation-anion layers is higher by 2 orders of magnitude than that across the cation-anion layers. Basing on the experimental data, we proposed the simple model of the charge carriage process.

Study of the Spectral Properties of Nanocomposites with CdSe Quantum Dots in a Wide Range of Low Temperatures

Luminescence spectra of the colloidal solution of CdSe quantum dots (in toluene) were studied in a wide range of low temperatures. Samples were synthesized in the liquid crystal matrix of cadmium octanoate (CdC8). A comparative analysis of the obtained data with previous results was performed.

Electro-conductive properties of cadmium octanoate composites with CdS nanoparticles

Electro-conductive properties of cadmium octanoate composites with CdS nanoparticles

Optical absorption, induced bleaching, and photoluminescence of CdSe nanoplatelets grown in cadmium octanoate matrix

CdSe nanoparticles (NPs) are chemically synthesized in thermotropic ionic liquid crystalline (LC) phase of cadmium octanoate that was used as a nanoreactor. The nanocomposite samples are obtained by the rapid cooling of the LC phase to room temperature. Observed doublet structure in absorption spectra of the nanocomposites is characteristic for the two-dimensional CdSe nanoplatelets (NPLs). The thicknesses of the CdSe NPLs are 1.6, 1.9 and 2.3 nm as determined from the absorption spectra, and correspond to 4, 5 and 6 CdSe monolayers, respectively. Induced simultaneous bleaching of the doublet components observed under femtosecond laser excitation, as well as photoluminescence spectra and their kinetics are found compatible with the model of excitons with heavy- and light-hole valence bands confined in nanoplatelets.

Luminescence properties of CdSe nanocrystallites in cadmium alkanoate glasses

Quantum confinement effect and its influence on absorption and photoluminescence spectra of CdSe nanoparticles chemically synthesized in thermotropic ionic liquid crystal of cadmium octanoate are studied. It was found out that the spectral resolution grows with decrease of temperature, so it becomes possible to distinguish the band-edge luminescence from the bands associated with the presence of surface defects. Obtained spectra were analyzed theoretically and the energy diagrams for samples with 1.8 nm and 2.6 nm nanoparticles were calculated.

Monodispersity and ordering of semiconductor quantum dots synthesised in ionic liquid crystalline phase of cadmium alkanoates

Structural and optical properties of cadmium alkanoates nanocomposites with cadmium sulfide (CdS) quantum dots (QDs) have been studied by using various techniques: small angle X-ray scattering, transmission electron microscopy, optical absorption spectroscopy and photoluminescence. QDs are chemically synthesised in thermotropic ionic liquid crystalline (ILC) phase of cadmium alkanoates that have smectic-type ordering and are used as nanoreactors. Anisotropic glassy nanocomposites are obtained by rapid cooling the thermotropic ILC nanocomposites to the room temperature. For synthesis of CdS QDs are used cadmium capronate matrix or cadmium octanoate matrix and their binary mixture. Our results show that in the new cadmium alkanoates matrices, the CdS QDs have a small dispersion of their sizes, their shape is nearly spherical, they are stable over time and they are ordered in a layered smectic A matrix. QDs in cadmium octanoate and in cadmium capronate matrices have the dominant characteristic sizes of 2.7 and 2.8 nm, respectively. In the binary mixture, the QDs have two dominant characteristic sizes of 2.7 and 3.6 nm. The glassy nanocomposites show spectra both of absorption and of photoluminescence in near-ultraviolet and blue visible spectral range.

Strong thermal optical nonlinearity caused by CdSe nanoparticles synthesised in smectic ionic liquid crystal

Spectral and nonlinear optical properties of cadmium octanoate composites containing CdSe nanoparticles (NPs) have been studied by using optical absorption spectroscopy and laser scanning technique (Z-scan). CdSe NPs are chemically synthesised in thermotropic ionic liquid crystal (ILC) phase of cadmium octanoate which is used as nanoreactor. Anisotropic glassy nanocomposites are obtained by the rapid cooling of the ILC phase of nanocomposites to room temperature. The sizes of the CdSe NPs are determined from the absorption spectra. The thermo-optical nonlinearity of the new nanocomposites is characterised by extremely large value of the nonlinear refractive index, n2, under relatively low-powered CW laser irradiation. This nonlinearity is caused by (1) the efficient light-induced heating due to the CdSe NPs strong exciton absorption, and (2) consequent thermal dissipation, which in turn, produces the photoelastic tensions in the glassy smectic matrix.