Dr. K. N. Venkatachalaiah

Herein, we report hierarchical arrow-like structures of CaZrO3:Dy3+ (1−11 mol %) are prepared by sonochemical route using bio template as a surfactant. High purity and crystallinity of the product was obtained in sonochemical route when compared to conventional methods. Morphological results showed arrow-like structures which are highly reliant on many experimental parameters such as, sonication time, bio-template concentration, sonication power, pH and surfactant to water ratio. The photoluminescence emission spectra consist of sharp peaks at ∼481 nm (blue), 575 nm (yellow) and 665 nm (red), which ascribed to 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions of Dy3+ ions, respectively. The decrement in the photoluminescence emission intensity after 7 mol % of Dy3+ ion concentration was clearly noticed, which may due to concentration quenching. The photometric properties of the prepared samples showed intense white emission with high color purity. Thermoluminescence glow curves of CaZrO3:Dy3+ (7 mol %) showed broad and intense peak at ∼143 °C at a warming rate of 2 °C s−1. Thermoluminescence profile reveals the linear dependence with dose, least fading and highly reproducible. The optimized powders are employed to image the latent fingerprints with higher resolution on various porous, non-porous and semi-porous surfaces. The aforementioned results clearly indicate that the optimized hierarchical structures are effectively used in radiation dosimetry, display devices and advanced forensic applications.

Mimosa pudica(MP) plant extract was used to prepare Y2O3:Tm3+ (1-11mol %) nanoscale superstructure with nitrate source as precursors. The samples were characterized by advanced characterization techniques. The PXRD peaks indicates crystalline, no impurity peaks were present with body centre cubic structure of Y2O3. Photoluminescence emission spectra shows blue color emission at 358 nm excitation wavelength. The major peak of Tm3+ was at 453 nm and two very weak peaks were observed at ∼ 474 nm attributed to the transitions of 1D2 → 3 F4 and 1G4 → 3H6, res. The calculated color co-ordinates were matches to the NTSC blue color. Correlated color temperature was ∼ 4000 K. So the Y2O3:Tm3+ nanophosphor could be used for blue component in the warm WLED and SSL devices.

Sm3+ doped (1-11 mol %) cubic Y2O3 nanoflowers were fabricated by simple low temperature Sonochemical method using Aloe Vera gel as fuel. The product was characterized by PXRD, SEM, TEM, DRS, PL etc. The powder X-ray diffraction (PXRD) profiles of nanophosphors showed cubic phase structure. The particle size was further confirmed by transmission electron microscope (TEM) and it was found to be in the range of 17-25 nm. The PL emission results reveal that the phosphor nanoparticles (NPs) emit an intensive yellowish light under 367 nm excitation. The excitation spectrum of Y2O3: Sm3+ (5 mol %) obtained by monitoring the emission of the 4f - 4f (4G5/2→6H7/2) transition of Sm3+ at 612 nm As can be seen that the excitation spectrum consists of strong band at 332 nm and a broad band centered at 367 nm which corresponds to host absorption, confirming the effective energy transfer from Y2O3 host to Sm3+ ions. In the present study, CIE and CCT were estimated and found to be (0.45688, 0.51727) and the CCT of Y2O3: Sm3+ at 367 nm excitation was found to be 3357 K which was within the range of vertical daylight. Thus it can be useful for artificial production of illumination devices.

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 Scherer's 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 (WLED's).

Blue light emitting neodymium (Nd) doped dicalcium (Ca2SiO4) silicate nanostructures were prepared for the first time via ultrasound assisted sonochemical synthesis route using cetyltrimethylammonium bromide (CTAB) surfactant. The obtained final product was well characterized. The powder X-ray diffraction (PXRD) profiles confirmed that product was highly crystalline in nature with monoclinic phase. Influence of various reaction parameters such as, the effect of sonication time, concentration of the surfactant and pH of the precursor solution on the morphology was studied in detail. Diffuse reflectance spectroscopy (DRS) was studied to evaluate the band gap energy of the products and the values were found in the range of 5.78 – 6.17 eV. The particle size was estimated by transmission electron microscope (TEM) and it was found in the range of 20-30 nm. Photoluminescence (PL) properties were studied in detail by recording emission spectra of all the Nd doped dicalcium silicate nanostructures at an excitation wavelength of 380 nm. The emission peaks were observed at 469, 520, 545 and 627 nm which corresponds to Nd3+ ion transitions. The 7 mol% Nd3+ doped Ca2SiO4 nanostructures showed maximum intensity. Further photometric measurements were done by evaluating, Commission International De I-Eclairage (CIE) and correlated color temperature (CCT). From CIE it was observed that the color coordinates lies in blue-green region, which slightly shifts to green as the Nd3+ concentration increases. The color purity and quantum efficiency were also estimated and the results indicate that the nanophosphor obtained in this route can be used in preparing light emitting diodes with a blue-green emission as prominent color.

Nano research offered new possibilities in surface-based science includes latent fingerprints and lips print detection on various surfaces. CdSiO3:Dy3+ nanopowders were fabricated via modified sonochemical method. Eccrine prints stained by optimized composition of prepared samples exhibited high sensitivity, low background hindrance on various surfaces compared to traditional fluorescent powders. Surface morphologies were studied with different sonication influential parameters. The estimated average crystallites size and band gap were found to be 22 nm and 5.37 eV respectively. Photometric CIE and CCT values were close to near ultraviolet light with CP of 95% for the prepared compounds confirms their utility in the field of optoelectronics.

Facile solution combustion route was used to prepare the optimized composite core shell SiO2@Y2O3:Eu3+, Li+ fluorescent nanopowders (NPs) with superior fluorescence intensity under UV light. Powder dusting technique was used for the visualization of latent fingerprints (LFPs) on different porous and non-porous surfaces. The results display that the amorphous SiO2 microspheres were covered by crystalline Y2O3:Eu3+, Li+ NPs, resulting in spherical core-shell structure. The phosphors exhibit intense pure strong red emission corresponding to characteristic Eu3+ ions 5D0→ 7F2 transitions under NUV excitation. The CIE co-ordinates were found to be (x = 0.63, y = 0.36) which is very close to standard NTSC values (x = 0.67, y = 0.33). Judd-Ofelt theory was used to estimate the intensity parameters (Ω2 and Ω4) as well as radiative properties. The CCT value was ∼ 3475 K which was less than 5000 K, as a result the phosphor was highly useful in warm light emitting diodes. Thus, results presented confirms that the developed method was simple, fast and optimized phosphor was effectively used for multifunctional applications namely luminescent sensor for visualization of LFPs, solid state lightning and security ink applications.

In the past two decades, organic conductors have been widely explored for use in different applications. One of the extensively studied organic material for the use in the field of electronic devices is PEDOT:PSS. Organic/inorganic nanocomposite systems have been developed to improve the properties of organic materials. In the present study, we have made an attempt to understand the effect of low energy oxygen ion beam irradiation on the electrical and structural properties of PEDOT:PSS and PEDOT:PSS/TiO2 nanocomposites. The observed reduction in electrical properties in PEDOT:PSS systems may be linked to radiation induced phase change. The nanocomposite systems show better stability to the ion irradiation compared to the pure systems. © 2016 Author(s).