Model representing growth mechanism in the LB thin film during phase transformation from α- to β-phase on annealing.

In this work we have studied the structural and optical properties of ZnO thin films prepared by sol-gel spin
coating process. Zinc acetate dihydrate was used as the precursor material. Thin films of ZnO were prepared on
Quartz substrate post annealed at 400ºC, 500ºC and 600ºC. X-ray diffraction (XRD) of the films showed
polycrystalline nature. Scherrer’s formula was used to calculate crystallite size. Scanning electron microscopy
(SEM) study showed granular surface. The refractive index, extinction coefficient and thickness of the films
were measured with spectroscopic Ellipsometry. The band gap and Urbach energy were calculated. The
photoluminescence measurement revealed UV emission at ~ 380 nm.

A search for novel organic luminogens led us to design and synthesize some N-fused imidazole derivatives based on imidazo[1,2-a]pyridine as the core and arylamine and imidazole as the peripheral groups. The fluorophores were synthesized through a multicomponent cascade reaction (A(3) coupling) of a heterocyclic azine with an aldehyde and alkyne, followed by Suzuki coupling and a multicomponent cyclization reaction. All of the compounds exhibited interesting photophysical responses, especially arylamine-containing derivatives, which displayed strong positive solvatochromism in the emission spectra that indicated a more polar excited state owing to an efficient charge migration from the donor arylamine to the imidazo[1,2-a]pyridine acceptor. The quantum yields ranged from 0.2 to 0.7 and depended on the substitution pattern, most notably that based on the donor group at the C2 position. Moreover, the influence of general and specific solvent effects on the photophysical properties of the fluorophores was discussed with four-parameter Catalán and Kamlet-Taft solvent scales. The excellent thermal, electrochemical, and morphological stability of the compounds was explored by cyclic voltammetry, thermogravimetric analysis, and AFM methods. Furthermore, to understand the structure, bonding, and band gap of the molecules, DFT calculations were performed. The performance of the electroluminescence behavior of the imidazo[1,2-a]pyridine derivative was investigated by fabricating a multilayer organic light-emitting diode with a configuration of ITO/NPB (60 nm)/EML (40 nm)/BCP (15 nm)/Alq3 (20 nm)/LiF (0.5 nm)/Al(100 nm) (ITO=indium tin oxide, EML=emissive layer, BCP=2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, Alq3 =tris(8-hydroxyquinolinato)aluminum), which exhibited white emission with a turn-on voltage of 8 V and a brightness of 22 cd m(-2).

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This article presents a comprehensive experimental study of optical properties of Li-doped ZnO nanorods grown by a low temperature (300 °C) thermal decomposition method. In particular, a study of the room temperature photoluminescence spectra dependence on the Li concentration is presented here. The doping of Li in ZnO nanorods results in a redshift in near band edge emission (NBE) compared to the undoped ZnO nanorods. Depending on the Li concentration, we observe a green emission in Photoluminescence spectra. The possible physical mechanisms governing the visible region luminescence are also discussed. These results show that Li-doped ZnO nanorods with strong visible region luminescence have potential applications in optoelectronic devices.

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