Preparation of Eu3+ ions activated Ca2La8(SiO4)6O2 oxyapatite nanophosphors through two-step surfactant-free method and their optical and electrical properties.

Eu3+ ions activated Ca2La8(SiO4)6O2 (CLSO):Eu3+ nanophosphor samples were synthesized by a mixed solvothermal and hydrothermal method. The samples were carefully studied using various characterization techniques. The XRD patterns of CLSO:Eu3+ and CLSO confirmed that the samples were crystallized in hexagonal phase with a space group of P63/m (176). The morphology of the nanoparticles was studied by varying the reaction parameters such as growth, temperature and time. The photoluminescence (PL) excitation and PL emission spectra exhibited the typical Eu3+ bands in the wavelength range of 200-550 nm and 400-750 nm, respectively. The intensity of the [Formula: see text] electric dipole (ED) transition peak was strong in the PL emission spectrum which imparts the red color when observed under ultraviolet light. The ED transition peak intensity increased when the sample was calcined at an elevated temperature of 700 °C, indicating improved asymmetry ratio and good chromaticity coordinates. The electrical properties of the prepared materials were studied by spin-coating the powder dispersed solutions on the silica substrate. The output current values were also measured for the CLSO nanoparticles prepared under different growth conditions. These results showed the advantages of CLSO nanoparticles for their application in optics and feasibility in nanoelectronic and energy harvesting devices.

Synthesis and luminescent properties of Eu3+ activated SrWO4 nanocrystalline microspheres.

We synthesized the Eu3+ activated SrWO4 nanocrystalline microspheres by a simple and facile synthesis route. X-ray diffraction patterns exhibited a unique phase of SrWO4:Eu3+ scheelite structure with an average crystallite size of 58.9 nm. Fourier transform infrared spectra revealed the presence of absorption bands of WO4(2-) and polyethylene glycol. The optical properties were investigated by varying the Eu3+ ion concentration. Photoluminescence (PL) excitation spectra confirmed that these phosphors are able to be excited by UV, near UV, and visible wavelengths. PL emission spectra showed the bright-red emission due to the 5D0 --> 7F2 electric dipole transition from the sites of non-inversion symmetry. The optimal doping concentration of Eu3+ ions was found to be 7 mol%. Blending this phosphor with YAG:Ce3+ phosphors may compensate their lack of a red spectral component, which leads to a good natural white light for indoor illumination.

Fallen leaves derived honeycomb-like porous carbon as a metal-free and low-cost counter electrode for dye-sensitized solar cells with excellent tri-iodide reduction.

Utilizing carbon-based counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) have received much attention in recent times, owing to their low cost, good electrochemical activity, natural abundance and eco-friendly nature. Herein, we have facilely prepared quince leaves derived porous carbon (QLPC) using fallen quince leaves (QLs) and it was used as a cost-effective CE for the fabrication of DSSCs. By means of alkali treatment and pyrolysis process (at different temperatures of 700, 800 and 900 °C), the QLs powder undergoes chemical activation and carbonization, which results in a honeycomb-like QLPC with abundant micro/mesopores and large surface area. Simple and straightforward coating of QLPC samples onto fluorine doped tin oxide glass substrates led to improved electrocatalytic activity and good tri-iodide reduction in DSSCs. When the DSSCs were illuminated under 1 sun condition (AM 1.5; 100 mW cm-2), the device assembled with QLPC-based CE (prepared at 800 °C) showed a higher current density of ∼14.99 mA/cm2 and power conversion efficiency of ∼5.52% among the other QLPC-based CEs, which are comparable with the platinum-based CE in DSSCs. This facile process for the preparation of biomass derived carbon-based CE provides an alternative to the noble metal-free CE in DSSCs.

Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes.

The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350-420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.

Red and green colors emitting spherical-shaped calcium molybdate nanophosphors for enhanced latent fingerprint detection.

We report the synthesis of spherical-shaped rare-earth (Eu3+ and Tb3+) ions doped CaMoO4 nanoparticles in double solvents (IPA and H2O) with the help of autoclave. The X-ray diffraction patterns well match with the standard values and confirm the crystallization in a tetragonal phase with an I41/a (88) space group. The luminescence spectra exhibit the strong red and green emissions from Eu3+ and Tb3+ ions doped samples, respectively. The X-ray photoelectron spectroscopy results show the oxidation states of all the elements present in the sample. The temperature-dependent luminescence spectra reveal the stability of Eu3+ and Tb3+ ions doped samples. The red- and green-emitting Eu3+ and Tb3+ ions doped CaMoO4 samples were used for detection and enhancement of latent fingerprints which are the common evidences found at crime scenes. The enhanced latent fingerprints obtained on different surfaces have high contrast with low background interference. The minute details of the fingerprint which are useful for individualization are clearly observed with the help of these nanopowders.