G.P. Darshan

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.

Dual color emitting Eu doped strontium orthosilicate phosphors synthesized by bio-template assisted ultrasound for solid state lightning and display applications

A novel Sr2SiO4:Eu (1-5mol %) superstructures (SS) were synthesized using bio-sacrificial A.V. gel assisted ultrasound method. Powder X-ray diffraction patterns confirmed the presence of both α and β phase formation. It was evident that the morphological growth was highly reliant on A.V. gel concentration, sonication time, pH and sonication power. The formation mechanisms for different hierarchical SS were proposed. From diffuse reflectance spectra, the energy band gap was estimated and found to be ∼4.70-5.11eV. The photoluminescence emission spectra for the excitation at 392nm, shows characteristic emission peaks at 593, 613, 654 and 702nm which were attributed to 5D0→7F0, 7F1,7F2 and 7F3 transitions of Eu3+ ions respectively. Conversely, when the samples were subjected to the heat treatment at 850°C for 3h under argon atmosphere, display an intense broad emission peak with two de-convoluted peaks at 490 and 550nm due to 4f65d1→4f1 (8S7/2) transitions of Eu2+ ions. The concentration quenching phenomenon was discussed which attributes to energy transfer, electron-phonon coupling and ion-ion interaction. The Judd-Ofelt intensity parameters and other radiative properties were estimated by using emission spectra. The CIE chromaticity coordinate values of Sr2SiO4:Eu2+ and Eu3+ nanophosphors were located in green and red regions respectively. The calculated CCT and CRI values specify that the present phosphor can be fairly useful for both green and red components of white LEDs. Luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting diodes. Overall, the results elucidated a rapid, environmentally benign, cost-effective and convenient method for Sr2SiO4:Eu3+ synthesis and for the possible applications such as solid state lighting and display devices.

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.

Blue light emitting Y 2 O 3: Tm 3+ nanophosphors with tunable morphology obtained by bio-surfactant assisted sonochemical route

Modified sonochemical route was used to prepare Y2O3:Tm3+ (1-11mol%) nanophosphor using Mimosa pudica (M.P.) leaves extract as bio-surfactant. The prepared samples were exhibited high crystalline nature with various morphologies. This was due to sonochemical experimental reaction took place between cavitation bubbles and nearby solution. The average crystallite sizes of the prepared samples were about 15nm to 21nm as obtained from PXRD and TEM analysis. The ultraviolet visible absorption spectra showed prominent bands with an energy gap varied from 5.73eV to 5.84eV. Photoluminescence (PL) emission spectra shows the prominent blue light emission peak at ~456nm attributed to 1D2→3F4 transitions of Tm3+ ions. Judd-Ofelt intensity parameters were estimated by using PL emission spectra. The photometric characteristics of the prepared compounds were very close to the blue color of NTSC standards. So the results were fruitful in making use of Y2O3:Tm3+ nanophosphor as an alternative material for effective blue component in WLEDs.

SiO 2 @LaOF:Eu 3+ core-shell functional nanomaterials for sensitive visualization of latent fingerprints and WLED applications

For the first time, intense red color composite of SiO2@LaOF:Eu3+ core-shell nanostructures (NS) were fabricated via facile solvothermal method followed by thermal treatment. The obtained core-shell particles display better spherical shape and non-agglomeration with a narrow size distribution. Photoluminescence (PL) emission spectra exhibits intense peaks at ∼593 nm, 611 nm, 650 nm corresponds to 5D0 → 7FJ (J = 0, 1 and 2) Eu3+ transitions respectively. The spectral intensity parameters and Eu-O ligand behaviors are estimated by means of Judd-Ofelt (J-O) theory. CIE co-ordinates are found to be (x = 0.63, y = 0.36) which is very close to standard NTSC values (x = 0.67, y = 0.33). CCT value is ∼3475 K which is less than 5000 K, as a result this phosphor is suitable for warm light emitting diodes. The optimized core-shell SiO2 (coat III)@LaOF:Eu3+ (5 mol%) was used as a fluorescent labeling marker for the visualization of latent fingerprints on both porous and non-porous surfaces. Obtained fingerprints are highly sensitive and selective also no background hindrance which enables level-I to level-III fingerprint ridge characteristics. Observed results indicate that the significant improvement in luminescence of coreshell NS can be explored as a sensitive functional nanopowder for advanced forensic and solid state lightning applications.

New design of highly sensitive and selective MoO3:Eu3+ micro-rods: Probing of latent fingerprints visualization and anti-counterfeiting applications

Red colour light emitting Eu3+ ions activated MoO3 nanophosphors (NPs) were prepared through an ultrasound assisted sonochemical method using Aloe Vera (A.V.) gel as a bio-surfactant. Properties like crystal structure, morphology, optical band gap, luminescent properties, radiative parameters of prepared samples and their use in latent fingerprint (LFPs) visualization were reported. Powder X-ray diffraction results revealed the single orthorhombic crystal structure of the prepared samples, which specifies effective substitution of dopant ions. Morphology of NPs exhibits the hexagonal rod-like structures with size of ∼10 nm. Photoluminescence (PL) emission spectra exhibited sharp, intense peaks at ∼539 nm, 593 nm, 615 nm, 651 nm and 702 nm attributed to 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, 5D0 → 7F3 and 5D0 → 7F4 transitions of Eu3+ ions respectively. Judd-Ofelt (J-O) theory was used to estimate the PL intensity parameters and Eu-O ligand behavior. The International Commission on Illumination coordinates of the prepared samples located in the pure red region. The optimized sample can be explored as a novel sensing material for the visualization of LFPs on various surfaces under 254 nm UV light. Clear level-3 patterns (sweat pores) were observed in the LFPs and their decay was very slow compared to the LFPs obtained from commercial powders. The photometric characterization of the prepared samples reveals the suitability of the MoO3:Eu3+ NPs for pure red emission in light-emitting diode, better visualization of LFPs and anti-counterfeiting applications.