H.B. Premkumar

Effective fingerprint recognition technique using doped yttrium aluminate nano phosphor material

First time the yttrium aluminate nanoparticles are used to improve the fingerprint quality. Eco-friendly green combustion process is used to synthesize YAlO3:Sm(3+) (0.5-11mol%) nanophosphor using green tea leaf extract as non-toxic and eco-friendly fuel. Powder X-ray diffraction study confirms the orthorhombic phase. The average sizes of the crystallites were found to be in the range 20-35nm. The emission peaks centered at 564, 601 and 647nm is attributed to 4f-4f (4)G5/2→(6)HJ=5/2,7/2,9/2 forbidden transitions of Sm(3+) ions. Judd-Ofelt theory is applied to experimental data for providing qualitative support by determining J-O intensity parameters. The Commission International De I-Eclairage chromaticity co-ordinates are very close to National Television System Committee standard value of white emission (x=0.296, y=0.237). Further, correlated color temperature is found to be ∼11,900K. A simple, fast, highly sensitive and low-cost method for the detection and enhancement of fingermarks in a broad range of surfaces is developed and constitutes an alternative to traditional luminescent powders.

Novel EGCG assisted ultrasound synthesis of self-assembled Ca2SiO4:Eu3+ hierarchical superstructures: Photometric characteristics and LED applications

This paper reports for the first time ultrasound, EGCG assisted synthesis of pure and Eu(3+) (1-5mol%) activated Ca2SiO4 nanophosphors having self-assembled superstructures with high purity. The shape, size and morphology of the product were tuned by controlling influential parameters. It was found that morphology was highly dependent on EGCG concentration, sonication time, pH and sonication power. The probable formation mechanism for various hierarchical superstructures was proposed. The PL studies of Ca2SiO4:Eu(3+) phosphors can be effectively excited by the near ultraviolet (UV) (396nm) light and exhibited strong red emission around 613nm, which was attributed to the Eu(3+) ((5)D0→(7)F2) transition. The concentration quenching phenomenon was explained based on energy transfer between defect and Eu(3+) ions, electron-phonon coupling and Eu(3+)-Eu(3+) interaction. The Judd-Ofelt intensity parameters and radiative properties were estimated by using PL emission spectra. The photometric studies indicate that the obtained phosphors could be a promising red component for possible applications in the field of white light emitting diodes.

Spectroscopic and photoluminescence properties of MgO:Cr3+ nanosheets for WLEDs

Abstract This work explores the synthesis of nanocrystalline MgO:Cr3+ (1–9xa0mol%) nanophosphors via solution combustion route at 400xa0°C. The nanophosphors were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-Red (FTIR) spectroscopy. PXRD results confirm cubic phase and SEM micrographs indicate that the particles are highly porous and agglomerated. The TEM images show that the powder consists of spherical particles of size ∼5–15xa0nm. Upon 356xa0nm excitation the emission profile of MgO:Cr3+ exhibits an emission peak at 677xa0nm due to 2Egxa0→xa04A2g transition. It was observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity was observed for 3xa0mol% doped sample and afterward it decreases, attributed to concentration quenching. The resultant CIE chromaticity co-ordinates in the white region make the present phosphor highly useful for display applications and also for white light-emitting diodes (WLEDs).

Calotropis gigantean-assisted YSO:Pr3+ nanophosphors: Near-ultraviolet (NUV) photoluminescence and J-O analysis for solid-state lighting solutions

ABSTRACT Y2SiO5:Pr3+ (1–9 mol%) nanophosphors were prepared via combustion synthesis using Calotropis gigantea plant latex as fuel. The PXRD patterns of the sample revealed a monoclinic phase with phase group P21/C n.14. The crystallite size was found to be in the range of 40–48 nm. The effect of Pr3+ cations on the luminescence characteristics of YSO nanoparticles was studied. The CIE chromaticity coordinates were located in the yellow region. Hence, the present phosphor finds applications in light-emitting diodes and display devices.

Cicer arietinum fuel-blended facile synthesis, and structural, photometric, and antioxidant investigation of ZnO:Cr3+ nanophosphors for light-emitting display devices

ABSTRACT This article reports on the synthesis and physical properties of crystalline ZnO:Cr3+ nanophosphors by a low-temperature combustion route using a natural seed extract of Cicer arietinum as the fuel. The obtained product of ZnO:Cr3+ through the C. arietinum seed extract was investigated through various characterization techniques. It was evident that morphology was highly dependent on the concentration of seed extract. Emission spectra show two main intense characteristic peaks recorded at ∼593 and ∼688 nm which indicate that the optimized ZnO:Cr3+ nanophosphor was highly useful for red-light-emitting devices. The synthesized nanophosphors exhibit a significant antioxidant activity against the scavenging of DPPH-free radicals.