Venkatram Nalla

High‐Performance Broadband Photodetector Using Solution‐Processible PbSe–TiO2–Graphene Hybrids

Highly sensitive, multicomponent broadband photodetector devices are made from PbSe/graphene/TiO(2). TiO(2) and PbSe nanoparticles act as light harvesting photoactive materials from the UV to IR regions of the electromagnetic spectrum, while the graphene acts as a charge collector for both photogenerated holes and electrons under an applied electric field.

Transient photoconductivity and femtosecond nonlinear optical properties of a conjugated polymer-graphene oxide composite.

A water soluble conjugated thiophene polymer, sodium salt of poly[2-(3-thienyl)ethoxy-4-butylsulfonate] (TPP), and graphene oxide (GO) composite film (GO-TPP) device was prepared. Transient photoconductivity measurements were carried out on the GO-TPP composite film using 150 ns laser pulses of 527 nm wavelength. Highly efficient photocurrent generation was observed from the GO-TPP film. The relationships of the film photoconductivity, photocurrent decay time and electron decay times with the incident light intensity were investigated. The photoconductive gain of the film was determined to be greater than 40% and to be independent of the light intensity. Furthermore, the femtosecond nonlinear optical properties of the GO-TPP film were measured using 800 nm femtosecond laser pulses and the composite film exhibited high nonlinear absorption and nonlinear refraction coefficients.

Synthesis and nonlinear optical switching of Bi2S3 nanorods and enhancement in the NLO response of Bi2S3@Au nanorod-composites

Organic solvent dispersible bismuth(III) sulfide (Bi2S3) nanorods were prepared by the chemical decomposition of tris(monothiobenzoato) bismuth(III), [Bi(SCOPh)3] as a single molecular precursor in the presence of trioctylphosphine oxide (TOPO) and 1-dodecanethiol (DdT). The rod surfaces of the as-prepared Bi2S3 nanorods were attached to Au nanoparticles (NPs) via direct reduction of KAuCl4·2H2O in the presence of octylamine (OTA) and oleic acid (OA). The attachment of the Au NPs onto the Bi2S3 rod surfaces was found to be relatively stable. The prepared samples (both Bi2S3 and Bi2S3@Au) were characterized by powder X-ray diffraction (PXRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) analysis and UV-vis spectroscopy. Their nonlinear-absorption (NLA) responses were studied using laser pulses at 532, 780 and 1064 nm, and the observed enhancement in the NLO response of Bi2S3@Au was discussed. Optical switching behaviour was observed at all the wavelengths.

Charge transfer assisted nonlinear optical and photoconductive properties of CdS-AgInS2 nanocrystals grown in semiconducting polymers

Anisotropic CdS-AgInS2 nanocrystals are directly grown into benzothiadiazole-based semiconducting polymer solution. Their nonlinear optical absorption and nonlinear scattering are investigated with 7-ns laser pulses of 532-nm wavelength for optical limiting applications. Optical limiting is found to be enhanced in the polymer-CdS-AgInS2 nanocomposites, as compared to pure polymer or CdS-AgInS2 nanocrystals. The observation is explained quantitatively using a numerical model which includes one-photon-induced excited state absorption, two-photon absorption, and nonlinear scattering. Presence of charge transfer in polymer-CdS-AgInS2 nanocomposites is found from zero-biased photoconduction experiments, which plays an important role in the enhancement of nonlinear optical properties. In addition, it is also demonstrated that these nanocomposite films can be utilized for photodetection with large and fast photoconductive responses.

Enhanced photoluminescence due to two-photon enhanced three-photon absorption in Mn2+-doped ZnS quantum dots

In this work, we have investigated the multi-photon absorption induced photoluminescence in Mn2+-doped ZnS quantum dots in the wavelength range 860 – 1050 nm (Near-Infrared Window I). The observed three-photon action cross-section has been compared with the theoretical prediction under four band approximation. An enhancement of four to five orders has been observed in the range from 970 to 1050 nm compared to the theoretical value, which is attributed to two-photon enhanced three-photon absorption. Transient lifetime measurements reveal a lifetime of 0.35 ± 0.3 ms, which is four to five orders higher than other conventional fluorescent probes.