Anura P. Samantilleke

p-Type behaviour of electrodeposited ZnO:Cu films

Cu-doped ZnO (ZnO:Cu) thin films and ZnO/ZnO:Cu homojunction devices were electrodeposited on conductive glass substrates in a non-aqueous electrolyte containing Cu and Zn salts. The Cu content of the films is proportional to the Cu/Zn precursor ratio in the deposition electrolyte. ZnO:Cu was found to be of a hexagonal wurtzite structure with (002) preferred orientation. A transition from n-type to p-type was observed for ZnO:Cu films with a Cu/Zn ratio higher than 2% as inferred from the change in the direction of the photocurrent. The rectifying characteristics shown by homojunction devices further confirm the p-type conductivity of ZnO:Cu layers.

Cohesive strength of nanocrystalline ZnO:Ga thin films deposited at room temperature.

In this study, transparent conducting nanocrystalline ZnO:Ga (GZO) films were deposited by dc magnetron sputtering at room temperature on polymers (and glass for comparison). Electrical resistivities of 8.8 × 10-4 and 2.2 × 10-3 Ω cm were obtained for films deposited on glass and polymers, respectively. The crack onset strain (COS) and the cohesive strength of the coatings were investigated by means of tensile testing. The COS is similar for different GZO coatings and occurs for nominal strains approx. 1%. The cohesive strength of coatings, which was evaluated from the initial part of the crack density evolution, was found to be between 1.3 and 1.4 GPa. For these calculations, a Youngs modulus of 112 GPa was used, evaluated by nanoindentation.

Preparation and Photoluminescence Properties of SrAl2O4:Eu2+,RE3+ Green Nanophosphors for Display Device Applications

An efficient rapid gel combustion process was used to prepare divalent-europium-doped strontium aluminate (SrAl2O4:Eu2+/Eu2+,Dy3+/Eu2+,Dy3+,Nd3+) nanophosphors in the presence of boron flux in air. The prepared nanophosphors emitted green light at 507xa0nm upon excitation at 360xa0nm. The emission of green light was observed due to the 4f65d1xa0→xa04f7 transition of Eu2+ ions. The absence of the characteristic sharp emission peak at 612xa0nm for Eu3+ (5D0xa0→xa07F2) indicates that efficient reduction of Eu3+ to Eu2+ occurred in the presence of the boron flux (H3BO3) as reducing agent. The x-ray diffraction pattern suggested monoclinic crystallinity, while transmission electron microscopy revealed the average size of the prepared materials to be between 20xa0nm and 50xa0nm. Coactivators in the lattices such as Dy3+ alone or Dy3+ with Nd3+ produced long persistence and enhancement of the optoelectronic properties of the prepared materials.

Nanostructured hybrid ZnO thin films for energy conversion

We report on hybrid films based on ZnO/organic dye prepared by electrodeposition using tetrasulfonated copper phthalocyanines (TS-CuPc) and Eosin-Y (EoY). Both the morphology and porosity of hybrid ZnO films are highly dependent on the type of dyes used in the synthesis. High photosensitivity was observed for ZnO/EoY films, while a very weak photoresponse was obtained for ZnO/TS-CuPc films. Despite a higher absorption coefficient of TS-CuPc than EoY, in ZnO/EoY hybrid films, the excited photoelectrons between the EoY levels can be extracted through ZnO, and the porosity of ZnO/EoY can also be controlled.

Synthesis of Sr(1-x-y)Al4O7:Eux2+,Lny3+ (Ln = Dy, Y, Pr) nanophosphors using rapid gel combustion process and their down conversion characteristics

Eu2+ and Eu2++Ln3+ doped SrAl4O7 nanophosphors were synthesized by rapid gel combustion process. The morphology of prepared phosphors was examined with scanning and transmission electron microscopy. The phase identification and the crystal structures of nanophosphors were studied using X-ray powder diffraction techniques. Luminescence characteristics of the prepared nanophosphors were analyzed on account of excitation, emission and phosphorescence decay analysis. The emission spectra demonstrated the broad green emission attributed to 4f65d1→ 4f7 transition of the Eu2+ ions. The effect of codoping of some trivalent lanthanide (Dy3+, Pr3+ and Y3+) ions were investigated for improving the emission intensity and phosphorescence decay time of the basic lattice of SrAl4O7:Eu2+ phosphors. The synthesized materials had enhanced bright luminescent properties that could suitably be applied for display as well as photovoltaic applications.

Synthesis and Optical Characterization of Europium Doped MY2O4 (M = Mg, Ca, and Sr) Nanophosphors for Solid State Lightening Applications

Trivalent europium doped yttriate nanophosphors were synthesized by rapid facile gel combustion technique. The photoluminescence (PL) properties of these Eu3

Optoelectronic characterization of Eu3+ doped MLa2O4 (M = Sr, Ca, Mg) nanophosphors for display devices

Abstract Eu3+ doped MLa2O4 (M = Mg, Ca, Sr) nanophosphors were synthesized by a rapid facile gel combustion route. Luminescence properties of these prepared nanophosphors were analyzed by their excitation and emission spectra. The excitation spectrum consisted of some peaks in the 350–410 nm range due to the f–f transitions. The emission spectra of prepared nanophosphors had transitions of Eu3+ ions i.e. 5D0 → 7F0 (580 nm), 5D0 → 7F1 (594–596 nm), 5D0 → 7F2 (614–618, 628–629 nm), and 5D0 → 7F3 (650–651 nm). The main emission peak was observed at 614–618 nm of 5D0→7F2 transitions of Eu3+ ions. The enhancement in optical properties was observed when materials were reheated at higher temperatures. The nanostructural morphology was confirmed with scanning as well as transmission electron microscopy. The prepared materials were having size in the range of 10–50 nm. X-ray powder diffraction (XRD) technique was used to determine the crystal structure and phase of the prepared phosphor materials. XRD measurements revealed that the crystallinity of MLa2O4 materials increased with increasing the sintering temperature. The prepared materials had bright red emitting optical properties that could be suitably applied in various display devices.

Formation of unique nanocrystalline Cu-In-Se bulk pn homojunctions for opto-electronic devices.

Semiconductor pn junctions, integrated in optoelectronic devices require high quality crystals, made by expensive, technically difficult processes. Bulk heterojunction (BHJ) structures offer practical alternatives to circumvent the cost, flexibility and scale-up challenges of crystalline planar pn junctions. Fabrication methods for the current organic or inorganic BHJ structures invariably create interface mismatch and low doping issues. To overcome such issues, we devised an innovative approach, founded on novel inorganic material system that ensued from single-step electrodeposited copper-indium-selenide compounds. Surface analytical microscopies and spectroscopies reveal unusual phenomena, electro-optical properties and quantum effects. They support the formation of highly-ordered, sharp, abrupt 3-dimensional nanoscale pn BHJs that facilitate efficient charge carrier separation and transport, and essentially perform the same functions as crystalline planar pn junctions. This approach offers a low-cost processing platform to create nanocrystalline films, with the attributes necessary for efficient BHJ operation. It allows roll-to-roll processing of flexible devices in simple thin-film form factor.

A versatile fluorescence lifetime imaging system for scanning large areas with high time and spatial resolution

We present a flexible fluorescence lifetime imaging device which can be employed to scan large sample areas with a spatial resolution adjustable from many micrometers down to sub-micrometers and a temporal resolution of 20 picoseconds. Several different applications of the system will be presented including protein microarrays analysis, the scanning of historical samples, evaluation of solar cell surfaces and nanocrystalline organic crystals embedded in electrospun polymeric nanofibers. Energy transfer processes within semiconductor quantum dot superstructures as well as between dye probes and graphene layers were also investigated.

ZnO:Cu Thin Films and p‐n Homojunctions Grown by Electrochemical Deposition

ZnO doped with Cu thin films were deposited on indium tin oxide coated glass substrates by electrodeposition using an electrolyte consisting of Cu and Zn perchlorates dissolved in dimethylsulfoxide. The Cu/Zn ratio measured in the thin films is about twice the Cu/Zn ratio present in the starting electrolyte. Irrespective of the Cu content, all the ZnO:Cu films exhibit a hexagonal wurtzite structure typical of ZnO with a preferential orientation along (002) direction. The p‐type behaviour of ZnO:Cu films is inferred from the change in the sign of the photocurrent observed for Cu concentrations greater than 2%. Furthermore, a p‐n homojunction with a rectifying factor ∼22 were prepared by electrodepositing of ZnO/ZnO:Cu layers.