S. Som

Effect of annealing on the structural, morphological and photoluminescence properties of ZnO thin films prepared by spin coating

Zinc oxide (ZnO) thin films were deposited on silicon substrates by a sol-gel method using the spin coating technique. The ZnO films were annealed at 700°C in an oxygen environment using different annealing times ranging from 1 to 4 h. It was observed that all the annealed films exhibited a hexagonal wurtzite structure. The particle size increased from 65 to 160 nm with the increase in annealing time, while the roughness of the films increased from 2.3 to 10.6 nm with the increase in the annealing time. Si diffusion from the substrate into the ZnO layer occurred during the annealing process. It is likely that the Si and O2 influenced the emission of the ZnO by reducing the amount of Zn defects and the creation of new oxygen related defects during annealing in the O2 atmosphere. The emission intensity was found to be dependent on the reflectance of the thin films.

The role of surface and deep-level defects on the emission of tin oxide quantum dots

This paper reports on the role of surface and deep-level defects on the blue emission of tin oxide quantum dots (SnO₂ QDs) synthesized by the solution-combustion method at different combustion temperatures. X-ray diffraction studies showed the formation of a single rutile SnO₂ phase with a tetragonal lattice structure. High resolution transmission electron microscopy studies revealed an increase in the average dot size from 2.2 to 3.6 nm with an increase of the combustion temperature from 350 to 550 °C. A decrease in the band gap value from 3.37 to 2.76 eV was observed with the increase in dot size due to the quantum confinement effect. The photoluminescence emission was measured for excitation at 325 nm and it showed a broad blue emission band for all the combustion temperatures studied. This was due to the creation of various oxygen and tin vacancies/defects as confirmed by x-ray photoelectron spectroscopy data. The origin of the blue emission in the SnO₂ QDs is discussed with the help of an energy band diagram.

Influence of ultrasonication times on the tunable colour emission of ZnO nanophosphors for lighting applications.

This paper reports on the sonochemical synthesis of zinc oxide (ZnO) nanophosphors (NPr) at different ultrasonication times (5 min, 30 min, 1h, 5h, 10h and 15 h) for near white light emission applications. X-ray photoelectron spectroscopy indicated that the O1s peak consists of two components. These were O1 (ZnO) and O2 (deficient oxygen; OH groups) centred at 529.7±0.3 eV and 531.1±0.3 eV, respectively. All samples showed UV and defect level emission (DLE). The DLE enhancement was due to the increase in oxygen related defects such as oxygen vacancies/interstitials. Due to the combination of near UV and DLE near white light emission in ZnO NPr was obtained. The emission could be tuned with different ultrasonic times. It was found that the ultrasonication time influenced the growth mechanism and luminescence properties of the ZnO NPr.

Synthesis and properties of poly(acrylamide-aniline)-grafted gum ghatti based nanospikes

In this work, we have synthesized poly(acrylamide-aniline)-grafted gum ghatti based crosslinked conducting hydrogel via a two-step synthesis method. The first step involved the microwave assisted synthesis of a semi-interpenetrating polymer network (semi-IPN) based on acrylamide and gum ghatti using N,N′-methylene-bis-acrylamide and ammonium persulfate as a crosslinker-initiator system. The semi-IPN has been observed to exhibit as much as 2183% swelling in aqueous solution. The effect of several variables such as time, solvent, pH, microwave power, crosslinker amount, aniline concentration, initiator concentration and monomer concentration on the swelling capacity was explored. In the final step, polyaniline was entrapped within a semi-IPN (optimized reaction condition) followed by doping with hydrochloric acid, which leads to the formation of conducting IPN. The synthesized hydrogels, as monitored by the swelling behaviour were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. Finally, the synthesized crosslinked networks have been used in malachite green (MG) adsorption. The result indicates that IPN of poly(acrylamide-aniline)-grafted gum ghatti are potential candidates for dye removal from water.

A study of the biodegradation behaviour of poly(methacrylic acid/aniline)-grafted gum ghatti by a soil burial method

Gum ghatti-based cross-linked hydrogels have been studied for their water absorption, flocculation and biodegradation properties. To date, a lot of research has been focused on gum ghatti-based cross-linked hydrogels; however, the synthesis and characterization of gum ghatti-based conductive biomaterials are relatively less explored. Moreover, the biodegradation and moisture retention studies have not been reported for conductive hydrogels. A gum ghatti-based electrically conductive hydrogel was prepared through a two-step aqueous polymerization. Biodegradation studies of the synthesized hydrogels were conducted using a soil burial test. Interpenetrating network structures showed better degradation efficiency than semi-IPN. The weight loss of semi-IPN and IPN was 66% and 86.6%, respectively, in 60 days. Different stages of degradation were studied using FTIR and SEM techniques. Furthermore, application of hydrogels to improve the water retention properties of different soils was studied for agricultural purposes, and it was found that the IPN hydrogel can improve the moisture retention capacity of soil for cultivation.

Dopant distribution and influence of sonication temperature on the pure red light emission of mixed oxide phosphor for solid state lighting

In this study, europium doped yttrium gadolinium (Y1.4Gd0.5Eu0.1O3) mixed oxide phosphors were synthesized by a sonochemical method at different growth temperatures (50°C, 100°C, 150°C and 200°C) for pure red light emission applications. The compositional identification, presence of dopants and the distribution of doping materials in the crystal lattice was studied by TOF-SIMS. The formation and growth mechanisms in the sonochemical synthesis of Y1.4Gd0.5Eu0.1O3 nanophosphors are discussed in detail. Different spectral and Judd-Ofelt parameters were estimated from photoluminescence data. Optical gain and efficiency parameters were calculated with the variation of synthesis environment and an efficient synthesis method to make good red emitting phosphors for solid-state lighting and display applications were proposed.

Evaluation of a conducting interpenetrating network based on gum ghatti-g-poly(acrylic acid-aniline) as a colon-specific delivery system for amoxicillin trihydrate and paracetamol

The objective of the present investigation was to develop colon-specific drug delivery systems for amoxicillin trihydrate and paracetamol using Gum ghatti (Gg) based cross-linked hydrogels. An interpenetrating network (IPN) of electrically active hydrogel based on Gg, poly(acrylic acid) (AA) and polyaniline was synthesized by a two-step aqueous polymerization. The radical copolymerization of Gg and AA was done using N,N′-methylene-bis-acrylamide (MBA) and ammonium persulphate (APS) as a crosslinker-initiator system. Optimum operating conditions for maximizing the percentage swelling were solvent (ml) = 10, AA (mol L−1) = 0.291 × 10−3, APS (mol L−1) = 0.219 × 10−1, MBA (mol L−1) = 0.324 × 10−1, reaction time (min) = 180, temperature (°C) = 60 and pH = 7.0. The synthesized semi-IPN matrix was further grafted with aniline through oxidative-radical copolymerization using APS in acidic media. The resultant cross-linked hydrogels were characterized using X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy, ToF-SIMS and electrical conductivity. The maximum conductivity was found to be 2.5 × 10−6 S cm−1 at 1.5 N HCl concentration. The synthesized hydrogels were loaded with amoxicillin trihydrate and paracetamol as model drugs to investigate the release behaviour. Amoxicillin trihydrate follows the surface phenomena and weak bonding interaction whereas paracetamol exhibited chemical interaction with the hydrogel matrices. The release rate of both the drugs through the synthesized hydrogel matrices was found to show Fickian behaviour at each pH. The hydrogel networks showed lower release in acidic and neutral media than in basic media, making them particularly suitable carriers for colon-specific drug delivery.

Influence of Ho3+ doping on the temperature sensing behavior of Er3+–Yb3+ doped La2CaZnO5 phosphor

In this paper, a series of Er3+/Yb3+ and Er3+/Yb3+/Ho3+ codoped La2CaZnO5 (LCZ) upconversion (UC) phosphors were synthesized by the combustion route. The UC emission from LCZ phosphors, codoped with fixed Er3+, Ho3+, and various Yb3+ concentrations has been investigated. The structural and upconversion properties of the synthesized phosphors were studied in detail. Under 980 nm laser excitation, the codoped samples showed green UC emission that consisted of three well-known emission bands centered at 522, 548 and 672 nm generated by the 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ ions, respectively. The emission intensities of these bands have been enhanced sufficiently on codoping of Yb3+ ions in the LCZ : Er3+ system. An effort has been presented to explain the enhancement on the basis of a power dependence study and an energy level diagram. The luminescence lifetimes of the green emission of the LCZ samples with different codoping were also recorded and incorporated to explain the energy transfer mechanism. The strong temperature dependence of the fluorescent intensity ratio between two green emissions makes the material suitable for temperature sensing purposes and it is also suitable up to high temperatures of 500 K. A relatively high-temperature sensor with good sensitivity 0.00625 K−1 was found from the observed results. An increment of 6% for the sensitivity is observed over the existing LCZ phosphor after co-doping with Ho3+. These results indicate that the Er3+/Ho3+/Yb3+ codoped LCZ material is an effective UC phosphor and may be a potential candidate for high-temperature sensors.

Ultra-broadband luminescent from a Bi doped CaO matrix

CaO:Bi phosphor powders were successfully synthesized by the sol–gel combustion method. Post heat treatment led to the enrichment of the Ca2+ site with multiple Bi centers. These centers were responsible for the change in the ultra-broadband cathodoluminescence (CL) emission as a function of different electron beam currents/beam voltages. The CaO phase formation and the presence of the enrichment of Bi was confirmed by using the X-ray diffraction and X-ray photoelectron spectroscopy techniques. The thermoluminescence afterglow spectra for the samples annealed at 800 °C and 1200 °C were strongly modified for the CaO and the presence of the multiple Bi centers. Of particular interest was that the ultra-broadband CL may have potential applications in inorganic single-emitting components that produce various colours under different beam currents/beam voltages or in a variety of optical devices if it can be better controlled.

Photoluminescence and thermoluminescence properties of Y3(Al,Ga)5O12:Tb3+ phosphor

A comparative study of the structural, photoluminescence (PL) and thermoluminescence (TL) properties of Y3(Al,Ga)5O12:Tb3+ phosphor powder was performed. The scanning electron microscope images showed that the phosphor particles were agglomerated and irregular in shape. The bigger particles consisted of smaller spherically shaped agglomerated particles ranging in size between 0.5 and 1 μm. The UV–VUV synchrotron radiation was used to study the luminescence properties of the phosphor. The TL study was performed after the sample was irradiated by γ-rays obtained from a 60Co target in the dose range of 10–50 Gy. The effect of heating rate on the TL glow curves and trapping parameters was also calculated. The correlation between PL and TL was explored.