R.B. Basavaraj

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.

Zinc silicates with tunable morphology by surfactant assisted sonochemical route suitable for NUV excitable white light emitting diodes.

The cationic surfactants assisted ultrasound route was used to prepare Dy3+ doped Zn2SiO4 nanophosphors. The final products were characterized by powder X-ray diffraction (PXRD), ultraviolet visible spectroscopy, scanning electron microscopy, transmission electron microscopy and photoluminescence. Orthorhombic phase of Zn2SiO4:Dy3+ (JCPDS card No. 35-1485) was confirmed from PXRD. It was evident that the morphology of spherical and broom like structures were obtained with epigallocatechin gallate (EGCG) and cetyltrimethylammonium bromide (CTAB) surfactants respectively. Further the size and agglomeration of the products were varied with surfactants concentration, sonication time, pH and sonication power. The probable formation mechanisms to obtain various micro/nano superstructures were discussed. The characteristic PL peaks were observed at 484, 574 and 666nm due to the electronic transitions 4F9/2→6Hj (j=15/2, 13/2, 11/2) of Dy3+ ions upon excited at NUV pumping wavelength of 350nm [6H15/2→6P7/2 (4M15/2)]. The Judd-Ofelt intensity parameters and radiative properties were estimated by using PL emission data. The photometric studies indicated that the obtained phosphors could be promising materials in white light emitting diodes (wLEDs). The present synthesis route was rapid, environmentally benign, cost-effective and useful for industrial applications such as solid state lighting and display devices.

Bio-mediated route for the synthesis of shape tunable Y2O3: Tb3+ nanoparticles: Photoluminescence and antibacterial properties

The study reports green mediated combustion route for the synthesis of Tb(3+) ion activated Y2O3 nanophosphors using Aloe Vera gel as fuel. The concentration of Tb(3+) plays a key role in controlling the morphology of Y2O3 nanostructures. The formation of different morphologies of Y2O3: Tb(3+) nanophosphors were characterized by PXRD, SEM, TEM and HRTEM. PXRD data and Rietveld analysis evident the formation of single phase Y2O3 with cubic crystal structure. The influence of Tb(3+) ion concentration on structural morphology, UV-visible absorption and PL emission were investigated systematically. The PL emission of Y2O3: Tb(3+) (1-11 mol%) nanophosphors were studied in detail under 271 and 304nm excitation wavelengths. The CIE coordinates lies well within green region and correlated color temperature values were found to be 6221 and 5562K under different excitations. Thus, the present phosphor can serve as an excellent candidate for LEDs. Further, prismatic Y2O3: Tb(3+) (3 mol%) nanophosphor showed significant antibacterial activity against Pseudomonas desmolyticum and Staphylococcus aureus. The present study successfully demonstrates Y2O3: Tb(3+) nanophosphors can be used for display applications as well as in medical applications for controlling pathogenic bacteria.

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.

Green light emitting nanostructures of Tb3+ doped LaOF prepared via ultrasound route applicable in display devices

For the first time Tb3+ (1-5 mol %) doped LaOF nanophosphors using Aloe vera (AV) leaves extract as bio-surfactant were synthesized by facile ultrasound supported sonochemical route at relatively high temperature (700°C) and short duration of 3h. The powder X-ray diffraction (PXRD) profiles of LaOF nanophosphors showed tetragonal structure. The morphological features of LaOF with effect of Sonication time and concentration of bio-surfactant were studied by scanning electron microscope (SEM). The particle size were estimated from transmission electron microscope (TEM) image was found to be in the range of 20-30 nm. The characteristic photoluminescence emission peaks at 487, 541, 586 and 620 nm in green region corresponding to 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+ were observed. The LaOF: Tb3+ nanophosphors exhibit green luminescence with better chromaticity coordinates, colour purity and higher intensity under low-voltage electron beam excitation were observed by Commission International De I’Eclairage (CIE) along with colour correlated temperature (CCT). All results indicate that these obtained nanophosphors have potential applications in field emission display device.For the first time Tb3+ (1-5 mol %) doped LaOF nanophosphors using Aloe vera (AV) leaves extract as bio-surfactant were synthesized by facile ultrasound supported sonochemical route at relatively high temperature (700°C) and short duration of 3h. The powder X-ray diffraction (PXRD) profiles of LaOF nanophosphors showed tetragonal structure. The morphological features of LaOF with effect of Sonication time and concentration of bio-surfactant were studied by scanning electron microscope (SEM). The particle size were estimated from transmission electron microscope (TEM) image was found to be in the range of 20-30 nm. The characteristic photoluminescence emission peaks at 487, 541, 586 and 620 nm in green region corresponding to 5D4→7Fj (j=6, 5, 4, 3) transitions of Tb3+ were observed. The LaOF: Tb3+ nanophosphors exhibit green luminescence with better chromaticity coordinates, colour purity and higher intensity under low-voltage electron beam excitation were observed by Commission International De I’Eclairag...

Synthesis, Characterization and Photoluminescence Properties of CdSiO3:Ce3+ Nanophosphors

CdSiO3: Ce3+ (1-11mol %) nanophosphors were prepared by low temperature solution combustion method using Oxalyl di-hydrazine (ODH) as fuel. The final products were well characterized by PXRD and SEM. The optical properties of the nanophosphors were investigated by Photoluminescence studies. PXRD results evident that CdSiO3 phosphor shows pure single monoclinic structure. The average crystallite size was calculated using Debye – Scherer’s formula and was found to be in the range of 30-40 nm. The SEM micrographs show phosphors with high porosity and irregular shaped particles. Photoluminescence peaks observed at 454, 563 and 679 nm under 397 nm excitation was due to transition from 5d state to the 2F5/2 and 2F7/2 components of the ground state of Ce3+ in CdSiO3 host material. CdSiO3:Ce3+ nanophosphors show an intense yellow emission with CIE coordinates (0.47, 0.50) with average correlated color temperature value 3284 was within the range of vertical day light. The present study successfully demonstrates solution combustion synthesis of nanophosphors for display 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.

Photoluminescence properties of Dy3+ activated Ca2SiO4 nanophosphor for WLED applications

ABSTRACT A series of Dy3+-activated Ca2SiO4 phosphors were prepared by low-temperature solution combustion method. The obtained phosphor was well characterized by powder X-ray diffraction, scanning electron microscopy, UV–visible spectroscopy, etc. The average crystallite size was estimated using Scherers formula and Williamson–Hall plots and was found to be in the range of 40–57 nm. The optical energy band gaps (Eg) for Dy-doped samples were estimated and were found to be in the range of 5.10–5.44 eV. The energy band gap was found to be widened with an increase of Dy3+ ion concentration. Photoluminescence spectra consist of three main groups of peaks in 460–500 nm (blue), 555–610 nm (yellow) and 677 nm (red) regions, respectively, and were assigned to the transitions of 4F9/2 → 6H15/2,13/2,11/2. The chromaticity color coordinates of all the prepared phosphors were found to be in the white region and was quite useful for the 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.