Anurag Pandey

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.

The role of growth atmosphere on the structural and optical quality of defect free ZnO films for strong ultraviolet emission

Highly c-axis oriented wurtzite structured ZnO thin films were deposited on silicon substrates using pulsed laser deposition (PLD) by ablating a ZnO target in different atmospheres, including vacuum, argon and oxygen in the deposition chamber. The stress in the films was shown to vary from −3.83 to −0.03 GPa as a function of the chamber atmosphere. The minimum compressive stress (−0.03 GPa) was observed for the oxygen atmosphere. X-ray photoelectron spectroscopy data indicated that the O1s peak consists of three components designated as O1 (due to ZnO), O2 (due to defects) and O3 (due to adsorbed species). A small defect level emission was obtained in the luminescence spectra of the ZnO film deposited in the oxygen atmosphere, while strong ultraviolet (UV) emission was observed for the ZnO films deposited in the vacuum and argon atmosphere. These PLD grown ZnO thin films have the potential to be used as sources of UV radiation in light emitting devices.

Spectroscopic Investigation of Up-Conversion Properties in Green Emitting BaMgF4:Yb3+,Tb3+ Phosphor

In this work we have comprehensively studied the up-conversion (UC) properties of BaMgF4:Yb3+,Tb3+ phosphor for the first time. BaMgF4:Yb3+,Tb3+ phosphors were prepared by a simple and low cost precipitation method. To determine the influence of dopant concentration on luminescence properties, the corresponding UC luminescence spectra of BaMgF4:Yb3+,Tb3+ phosphors were studied under NIR excitation. Emission spectra under NIR excitation reveal the vital role of Tb3+ concentration in spectral tuning from the blue to green region. The UC decay curves were also studied to explore the possible energy transfer (ET) mechanisms between Yb3+ and Tb3+. The results reported here are expected to provide an approach for better understanding ET mechanisms in many Yb3+/Tb3+ codoped UC phosphors. This study will be helpful in applications where precisely defined optical transitions is an essential criterion.

Efficient Color Tunable ZnWO 4 :Er 3+ -Yb 3+ Phosphor for High Temperature Sensing

The single monoclinic phase with nano-structured crystallites in the ZnWO4: Er3+ -Yb3+ phosphor have been detected from structural investigations by using the X-ray diffraction (XRD) analysis. The spectral studies performed in the codoped phosphor upon 980 nm excitation emit radiations within the UV- NIR wavelength region. Diffuse reflectance and Fourier transform infrared (FTIR) analysis have been done to identify the presence of active ions and impurities in the prepared phosphor. The pump power dependence study results in green to red intensity ratio variation and thus a tuning in color of emitted light is observed. The observed emissions have been explained on the basis of excited state absorption (ESA), energy transfer (ET), and temporal evolution analysis. The temperature sensing performance of synthesized material studied upto ~798 K results the highest sensor sensitivity of about 14.63 × 10-3 K-1 which confirms the suitability of present material for high temperature sensing with very good sensitivity.