R. Reshmi

Photoluminescence of Eu3 + -Doped Ba0.7Sr0.3TiO3 Thin Film for Optoelectronic Application

The europium-doped barium strontium titanate (BST:Eu) films find application in ferroelectric as well as in optoelectronic devices. In this paper, we report the pulsed laser deposition (PLD) of BST:Eu thin films. The structural and optical properties of the PLD-grown BST film have been investigated and correlated. The photoluminescence spectra show the prominent transitions of Eu 3+ ions at 550 nm ( 5 D 1 - 7 F 2 ), 615 nm ( 5 D 0 - 7 F 2 ), and 669 nm ( 5 D 0 - 7 F 3 ) upon excitation with 408 nm. The luminescent properties of BST:Eu thin films follow a close correlation with the crystallinity of the thin films. Films deposited at a lower substrate temperature show good luminescent characteristics.

Size-Dependent Optical Nonlinearity of Au Nanocrystals

Gold nanoparticles of different sizes are prepared by laser ablation of the gold target in deionized water. The UV/visible absorption spectra show surface plasmon resonance bands that are redshifted in wavelength with an increase in particle size. An increase in particle size is observed with increasing laser pulse energy. The optical absorptive nonlinearity of the nanoclusters shows an optical-limiting-type nonlinearity, which finds application in the fabrication of optical-limiting devices. The limiting efficiency decreases with an increase in particle size. The Au nanoparticle shows good nonlinear refraction, which is of a self-defocusing nature. Both the real and imaginary parts of nonlinear susceptibility increase with a decrease in particle size. A stable nonlinear

Determination of third-order optical absorptive nonlinearity of ZnO nanoparticles by Z-scan technique

A sensitive single-beam technique for measuring the nonlinear absorption coefficient of ZnO nanoparticles is reported here. The transmittance T(z) of the sample is measured by open aperture Z-scan technique as the sample is moved along the propagation path(z) of a focused Gaussian laser beam. The ZnO nanoparticles synthesized by wet chemical method, by mixing zinc acetate dehydrate and NaOH in ethanol is a clear transparent colloidal solution. The average size of ZnO nanoparticles is 6nm as confirmed by TEM analysis. Two-photon absorption of colloidal solutions of ZnO nanoparticles in ethanol is investigated by the Z-scan method using the nanosecond pulses from the second harmonics of Nd:YAG laser (532nm). The value of β for ZnO dispersed in ethanol extracted from the Z-scan data are 2.1cm/GW. ZnO nanoparticles of various sizes were embedded in PVA matrix on glass substrate and size dependence on β value was analyzed. The high value of two photon absorption coefficient (β) demonstrate that ZnO nanoparticle is a potential material for optical limiting applications.

Influence of Oxygen to Argon Ratio on the Properties of RF Magnetron Sputtered Ba0.7Sr0.3TiO3 Thin Films

The optical properties of thin films of barium strontium titanate (BST) are important due to its wide band gap, high refractive index and low absorption coefficient and hence find application in electro-optic and non-linear optical devices. Ba 0.7 Sr 0.3 TiO 3 (BST) thin films were deposited by RF magnetron sputtering on fused silica and Pt/TiO 2 /SiO 2 /Si (PtSi) wafers at relatively low substrate temperature. The crystallisation of thin films strongly depends on O 2 /Ar ratio in the sputtering gas. The optical parameters like band gap (E g ), refractive index (n) were studied as a function of oxygen to argon ratio in the sputtering gas. The electrical properties of BST thin films deposited on PtSi substrates as a function of O 2 to Ar ratio has also been studied. The films show 50% tunability with a minimum loss of 0.018 at 1 MHz when grown at the optimized O 2 to Ar ratio.

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr x Ti1−x O3) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.

Optical Emission Spectroscopic Analysis of Plasma Plume during Pulsed Laser Deposition of PZT

Spatial variation in intensity of spectral emission, electron temperature, number density, and the time of flight (TOF) of ions and neutrals at various oxygen ambiances has been investigated on ferroelectric lead zirconium titanate (PZT) plasma using optical emission spectroscopy. Plasma produced by ablating PZT ceramic target using Nd-YAG laser operating at the third harmonics ( nm,  ns, repetition frequency 10 Hz) was investigated at various oxygen partial pressures and at various distances from the target surface. Here energy density for laser fluence was fixed as 3.13 Jcm−2 and distance from the target and ambient gas pressure were varied. The electron number density and electron temperature of the PZT plasma at the early stage of plume expansion were measured as  Jcm−2 and 13200 K, respectively, and thus verified the existence of local thermodynamic equilibrium (LTE). Time of flight spectra (TOF) of neutral and singly ionized species in plasma were recorded. The result shows that plasma parameters and velocity of species are of same order for various oxygen partial pressures but have a decreasing tendency with distance. The energy of almost all species in the plume become more or less same at 0.1 mbar. These conditions favour the growth of perovskite PZT thin films.