Second Derivative Of Absorption Spectra Research Articles

Investigation of AgInS2/ZnS Quantum Dots by Magnetic Circular Dichroism Spectroscopy.

Over recent years, quantum dots (QDs) based on ternary metal dichalcogenides have attracted a lot of attention due to their unique properties and a range of potential applications. Here, we review the latest studies on the optical properties of AgInS2/ZnS QDs with emphasis on their theoretical modeling, and present our investigations of electronic transitions invisible in unstructured absorption spectra of AgInS2/ZnS QDs. The analysis of the absorption, photoluminescence excitation (PLE), and magnetic circular dichroism (MCD) spectra of hydrophobic and hydrophilic AgInS2/ZnS QDs of different sizes enables us to determine positions of electron transitions in these QDs. We demonstrate that the use of the second derivative of PLE spectra provides more unequivocal data on the position of the energy transitions compared with the second derivative of absorption spectra. Analysis of the MCD spectra reveals that the magnetic field induces energy level mixing in AgInS2/ZnS QDs in contrast to the traditional Cd-based QDs, where MCD is associated only with removing degeneracy of the excited energy level.

ZnO-doped KCl single crystal with enhanced UV emission lines

The embedded bulk KCl single crystal with the ZnO nanocrystal was grown using Czochralski technique. Various structural and optical analyses were employed to characterize the grown sample. X-ray diffraction confirmed the diffusion of ZnO NCs in the KCl bulk lattice. The crystal structure and the lattice parameters were estimated for both ZnO NCs and KCl matrix by Rietveld analysis. The bond formation of KCl:ZnO was demonstrated by Fourier transform infrared (FTIR) spectroscopy. FE-SEM was carried out for the morphological study of ZnO NCs and estimation of particle size distributions. Energy-dispersive X-ray (EDX) analysis was used to investigate the elemental composition of the prepared sample. The experimental results confirmed the improvement in optical properties of KCl single crystal was found when it was doped by ZnO. The second derivative of absorption spectrum confirmed the band gap of 6.06 eV for KCl single crystal. In PL spectrum, several intense UV light emission peaks at 297 and 360 nm were observed in which the emission peaks of KCl:ZnO samples were very sharp in comparison with the pure KCl single crystal. It seems that the UV peaks at 297 and 360 nm emission lines of ZnO-doped KCl crystals originated from electron capturing from F center.

Size Selective Excitonic Transition Energies in Strongly Confined CdSe Quantum Dots

We report on the synthesis of CdSe nanocrystal quantum dots (QDs) of different radii (R). Size dependent optical properties like increase in the confinement energy with decreasing radius for different excitonic transitions are studied. Different excitonic transitions are calculated from the second derivative of UV-vis absorption spectra of as synthesized CdSe QDs. The transitions are assigned to specific states by calculating the transition energies using effective mass approximation. A close matching of the transition energies with the experiment suggesting that the second derivative of the absorption spectra could provide a direct knowledge of the electronic transition for the direct band gap semiconductor quantum dots.

Electroabsorption spectroscopic study of cyano-substituted phenylene vinylene polymer (CN-PPV)

We report electroabsorption spectroscopy measurements on a single layer cyano-substituted phenylene vinylene (CN-PPV) polymer device and also contact potential difference (CPD) in the device structure ITO/PEDOT: PSS/CN-PPV/Al. The electroabsorption (EA) spectrum shows well developed structure of a peak and valley at 2.2 and 2.56 eV, respectively. It is demonstrated that the line shape more closely reflects second derivative of absorption spectra than corresponding first derivative. The origin of dominant features in EA spectra in the range of 1.5–3.2 eV are discussed qualitatively without taking recourse to fitting a linear combination of derivatives of linear absorption. The contact potential difference (CPD) measured using this technique shows a value 0.6 V that is exactly the work function difference between ITO and Al electrode used in this structure. These features in EA measurements of CN-PPV are in contrast to the ones observed in the case of PPV thin films.

Determination of lipid bilayer/water partition coefficient of new phenothiazines using the second derivative of absorption spectra method.

The partition coefficients (K(p)) between lipid bilayer of phosphatidylcholine (PC) vesicles and buffer for five new phenothiazines were determined using the second derivatives of ultraviolet absorption spectra. The lambda(max) of absorption band for each of the investigated phenothiazine derivatives (PDs) was shifted to the longer wavelengths in the presence of PC vesicles with increasing of lipid concentration. As a result of light scattering in liposome suspension no isosbestic point could be observed in absorption spectra. However, the background signal could be eliminated using the method of second derivative of absorption spectra. In the second derivative of absorption spectra two isosbestic points were observed. Changes of intensity (Delta D) of second derivative of absorption spectra at the lambda(max) (wavelength of absorption maximum for drug in buffer) caused by the increase in lipid concentration were measured for set of phenothiazine derivatives. K(p) for these drugs were calculated from the relationship between Delta D and lipid concentration. The K(p) values for all studied phenothiazine derivatives are in the order of magnitude of 10(5) and they increase about 1.7-fold when length of the alkyl phenothiazine chain was enhanced by addition of the each next one (-CH(2)) group. Substitution of -H atom by -CF(3) group at position 2 of phenothiazine ring results in 3.5-fold increase in K(p) values.