Study of the optical properties and frequency-dependent electrical modulus spectrum to the analysis of electric relaxation and conductivity effect in zinc oxide nanoparticles

Abstract

In this article, the optical and dielectric properties along with electric relaxation behaviour of the zinc oxide nanoparticles (ZnO NPs) with an average size & 32.5 nm were studied. The band gap, and free carrier concentration of the ZnO NPs have been found to be 3.73 eV, and & 5.55 9 10 12 per cm 3 , respectively. Dispersion parameters and nature of dispersion have been studied from optical spectrum. X-ray diffraction investigation revealed that the crystalline phase is hexagonal with atomic fraction & 75.44%. The overall behaviour of the dielectric constants of ZnO NPs has obeyed Koops model. Relaxation behaviour and defect state response inside ZnO NPs have been observed in the dielectric studies. The relaxation time varies from 8.0585 9 10 -5 to 7.8447 9 10 -5 s with temperature (T) ranges from 323 to 573 K, respectively, calculated from the electric modulus study. The AC conductivity complies the Jonscher's universal power law and the observed hopping of electron is the correlated barrier hopping. The activation energy of the ZnO NPs is found to be & 93 meV from the temperature-dependent DC conductivity analysis. The real part of complex impedance showed a negative temperature coefficient of resistance nature with increase the temperature from 473 to 673 K in the low-frequency zone. The equivalent circuit for the complex impedance analysis at T = 673 K has been studied from Cole-Cole equation and Nyquist plot. The observed properties of ZnO NPs are very important for electric storage, sensing and optical semiconductor devices.

Exciton–tryptophan coupling pulse behaviour along with corona formation, binding analysis, and interaction study of ZnO nanorod–serum albumin protein bioconjugate

“…Structural changes in the BSA and microenvironment changes [39,40] The apparent association constant of the complex at the peak position of the Trp was calculated from the Benesi and Hildebrand method and found to be 8 Â 10 3 mol À1 . [23] An important optical parameter is the refractive index (n), which can be expressed by the following equation [41] :…”

“…The variation of the refractive index (n) with λ of the bioconjugate shows (Figure 7a) an optical pulse-like nature with the mixture of anomalous and normal dispersions. [41] Different dispersion regions are: (i) normal dispersion regions: 230 nm < λ < 253 nm, 278 nm < λ < 303 nm, 376 nm < λ < 900 nm;…”

“…303 nm < λ < 353 nm. The optical conductivity (σ Opt ) can be expressed by the following relations [41] :…”

“…The real optical dielectric constant (ϵ 1 ) (Figure 8a), imaginary optical dielectric constant (ϵ 2 ) (Figure 8b) and electrical susceptibility (χ c ) (Figure 9a) could be expressed by the following equations [41] :…”

“…The above optical parameters (ϵ 1, ϵ 2, χ c ) showed an optical pulse-like nature with ϵ 1 > > ϵ 2 . This pulse 11T A B L E 3 The resultant fitted parameters for ZnO NRs-BSA bioconjugate from exponential association Equation 11Fitting parameters Trp Exciton For ZnO NRs, surface energy loss of function (SELF) and volume energy loss of function (VELF) can be expresses by the following equations [41] :…”