Gold nanosphere enhanced green and red fluorescence in ZnO: Al, Eu3+

Gold nanoparticles can generate near field due to surface plasmon resonance (SPR) in the visible region. Such near field has the ability to enhance fluorescence of optimally proximal emitters. We have observed augmented green (intrinsic) and red (Eu3+) emission under UV excitation (375 nm) from an important semiconductor ZnO:Al, Eu3+ when optimally conjugated with gold nanospheres. Local field generated by gold nanosphere (similar to 30 nm) is simulated through finite difference time domain method, and a direct correlation with fluorescence enhancement is established

Enhanced visible fluorescence in highly transparent Al-doped ZnO film by surface plasmon coupling of Ag nanoparticles

ZnO:Al (AZO) film has been deposited on quartz substrate by Pulsed laser deposition and showed monophasic hexagonal structure of c-axis oriented nanorods upto 80 nm in height. AZO film was optimally conjugated with Ag nanoparticles (Ag NPs) in a hybrid nanostructure to achieve significant enhancement in the visible fluorescence emission. Augmented near field and extinction spectra of shape tailored Ag NPs and their dimers are simulated through FDTD method, and a direct association with fluorescence enhancement is established. Such plasmon-enhanced visible emission from a transparent conducting oxide could be very important for solar cell applications

Performance analysis of anomalous photocatalytic activity of Cr-doped TiO2 nanoparticles [Cr(x)TiO2(1-x)]

We report the synthesis and characterisation of pristine and chromium (Cr) metal ion-doped titanium dioxide nanoparticles [Cr(x)TiO2(1-x)] to study the anomalous effect of Cr doping on the photocatalytic property of TiO2. The presence of dopants generates more number of recombination pairs and increases surface coverage sites which decreases photocatalytic activity. We study the structural morphology of the synthesised Cr(x)TiO2(1-x) samples using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy analysis. The effect of Cr3+ ions on the optical properties of TiO2 has been studied using various imaging and spectroscopic techniques. Further, the effect of doping of Cr on the photocatalytic activity of TiO2 has been analysed in detail. The concentration of Cr in TiO2 has been chosen as 0, 1, 5 and 10% by weight. It has been observed that the pristine TiO2 exhibits better photocatalytic activity as compared to Cr-doped TiO2 irrespective of the Cr concentration. This can be attributed to the fact that due to Cr doping in TiO2, the number of available adsorption sites for malachite green reduces which degrades its photocatalytic activity. It is also confirmed by photoluminescence (PL) and time-resolved photoluminescence spectroscopy. PL intensity increases, and lifetime decreases with increase in doping concentration. Radiative recombination of electron and hole pairs of Cr3+ in TiO2 degrades its photocatalytic activity. The degradation efficiency is found to be 96% in the case of pristine TiO2 which reduces to 12% when doped with x = 10% concentration of chromium. Therefore, it is observed that in comparison with Cr-doped TiO2, pristine TiO2 exhibits an improved photocatalytic activity which shows the anomalous effect of Cr doping on the photocatalytic property of TiO2

Introducing dual excitation and tunable dual emission in ZnO through selective lanthanide (Er3+/Ho3+) doping

We have introduced dual excitation properties in the multifunctional semiconductor ZnO by controlled solid state diffusion of dopant lanthanide ions like Er3+ and Ho3+ into the lattice at 500 degrees C. So far light emission from doped ZnO has been explored either under UV or IR excitation. Our results show that the emission colour can be tuned from cyan to red under UV (band edge, 377 nm) excitation and from green to red under IR (980 nm) excitation in ZnO through selected doping of lanthanide ions. Doping lanthanide ions in ZnO changes its morphology and emission characteristics. Whereas down conversion emission under UV excitation is due to across band gap excitation and subsequent donor-acceptor pair recombination, the dependence of up conversion emission yield on pump laser power indicates that two to three photon processes may be more effective in ZnO hosts for frequency upconversion

An empirical experimental observations and MD simulation data-based model for the material properties of confined fluids in nano/Angstrom size tubes

The transport of fluids in nanometer and Angstrom-sized pores has gotten much attention because of its potential uses in nanotechnology, energy storage, and healthcare sectors. Understanding the distinct material properties of fluids in such close confinement is critical for enhancing their performance in various applications. These properties dictate the fluid\u27s behavior and play a crucial role in determining flow dynamics, transport processes, and, ultimately, the performance of nanoscale devices. Remarkably, many researchers observed that the size of the geometry, such as the diameter of the confining nanotube, exerts a profound and intriguing influence on the material properties of nanoconfined fluids, including on the critical parameters such as density, viscosity, and slip length. Many researchers tried to model these material properties: viscosity $\eta$, density $\rho$, and slip $\lambda$ using various models with many dependencies on the tube diameter. It is somewhat confusing and tough to decide which model is appropriate and needs to be incorporated in the numerical simulation. In this paper, we tried to propose a simple single equation for each nano confined material property such as for density $\displaystyle \rho(D)/\rho_o = a+ b/(D-c)^n$, viscosity $\displaystyle \eta(D)/\eta_o = a+ b/(D-c)^n$, and the slip length $\lambda(D) = \lambda_1~D~e^{-n~D}+ \lambda_o$ (where $a,~b,~c,~n,~\lambda_1,~\lambda_o$ are the free fitting parameters). We model a wealth of previous experimental and MD simulation data from the literature using our proposed model for each material property of nanoconfined fluids at the nanometer and Angstrom scales. Our single proposed equation effectively captures and models all the data, even though many different models have been employed in the existing literature to describe the same material property. Our proposed model exhibits exceptional agreement with multiple independent datasets from the experimental observations and molecular dynamics simulations. Additionally, the model possesses the advantageous properties of continuity and a continuous derivative, so the proposed model is well-suited for integration into numerical simulations. Further, the proposed models also obey the far boundary conditions, i.e., when tube diameter $D \implies \infty$, the material properties tend to the bulk properties of the fluid. Due to the models\u27 simplicity, smooth, and generic nature, this heuristic model holds promise to apply in simulations to design and optimize nanoscale devices

Chemistry of extracting high-contrast invisible fingerprints from transparent and colored substrates using a novel phosphorescent label

Traditionally used fluorescent powders for developing invisible (latent) fingerprints involve complicated operation and show characteristics of auto-fluorescence interference and high toxicity. To overcome these serious drawbacks we report a novel application and facile methodology to extract high contrast fingerprints on non-porous and porous substrates using a chemically inert, visible light excitable, and nanosized SrAl2O4:Eu2+, Dy3+ phosphorescent label in the dark. The chemistry of non-covalent physisorption interaction between the long afterglow phosphor powder and sweat residue in fingerprints has been discussed in detail. Real-time fingerprint development on porous and non-porous substrates has also been performed

Probing high temperature ferromagnetism and its paramagnetic phase change due to Eu3+ incorporation in ZnO nanophosphors

Ferromagnetic oxide semiconductors exhibiting efficient luminescent properties together with robust ferromagnetism above room temperature form an exclusive class of spintronic materials endowed with both charge and spin degrees of freedom. Herein, we report on the occurrence of high temperature ferromagnetism (>600 K) in zinc oxide nanophosphors attributed to the presence of defects in the host lattice and wherein incorporation of rare earth ions contributed to a gradual reduction in the ferromagnetic character and steady transformation to paramagnetic behavior. Although undoped ZnO nanophosphors exhibit a high coercive field and saturation magnetization along with a prominent green emission (536 nm) attributed to the presence of oxygen vacancies V-o, Eu3+ doping results in a decrease in green emission along with coercivity as well as magnetization efficient line emission in the orange red region (618-622 nm) pointing to a definite correlation between the V-o and ferromagnetism. The temperature dependence of the magnetization shows stable ferromagnetism with Curie temperature above 600 K for undoped ZnO and a ferromagnetic to paramagnetic transition with an increase in Eu3+ concentration that has been explained through an F+ center exchange mechanism

Triple excitation with dual emission in paramagnetic ZnO:Er3+ nanocrystals

ZnO nanocrystals have been made excitable under UV as well as near and far infrared (IR) wavelengths (980 nm, 1550 nm) through doping of rare earth ion Er3+ thus making it a triple excitation nanophosphor. Whereas the visible emission under UV is broad due to intrinsic donor acceptor pair recombination, the sharp green and red emission peaks under IR are characteristic of f-f transitions of the Er3+ ion. Thus both down and upconversion fluorescence in ZnO could be realised through doping of rare earth ion Er3+ that also makes ZnO: Er3+ nanocrystals paramagnetic. To the best of our knowledge we are reporting upconversion at 1550 nm in ZnO: Er3+ for the first time

Novel flux-assisted synthesis for enhanced afterglow properties of (Ca,Zn) TiO3: Pr3+ phosphor

Selection of chemical fluxes for the phosphor synthesis is largely dependent on trial and error, so a detailed understanding of their selection is obligatory. The active role of various fluxes in influencing Pr3+ emission, afterglow, structural and morphological properties of the as-synthesized (Ca,Zn) TiO3: Pr(3+)phosphor is less explored. Luminescent properties of the (Ca, Zn) TiO3: Pr(3+)phosphors show a significant enhancement in Pr3+ emission with the addition of small quantities of fluxes. The persistence of the afterglow has also been increased to 15-30 min. Flux-dependent luminescent studies suggest that NH4BF4 is the best suitable flux for (Ca0.8Zn0.2) TiO3: Pr3+ phosphor among all others. X-ray diffraction studies confirm the orthorhombic phase of CaTiO3, in addition, low intensity peaks from cubic ZnTiO3 phase have also been observed. The calculated Commission Internationale de I'Eclairage (CIE) coordinates for the optimized (Ca0.8Zn0.2) TiO3: Pr3+ phosphor sample is found to be (0.66, 0.33), which is close to the ideal red coordinates with color purity of similar to 96.39%. Spatial distribution of the activator ions was investigated using confocal microscopy. Thermoluminescence studies have been carried out to understand the trapping and detrapping behavior of phosphors. This multifunctional phosphor could serve fascinating applications in areas involving photon energy storage systems, strategic markings, biological staining etc

Structural, morphological, photoluminescence and electrical characterization of aluminium doped ZnO phosphors for solar cell applications

We report synthesis of highly luminescent and n-type conducting aluminium doped ZnO (AZO) phosphors using flux-free solidstate reaction technique followed by casting of thin films. The precursor powders were pelletized and fired at 1000 degrees C (AZO-1). In another typical case, 2-stage sequential firing has been adapted at 1000 degrees C followed by 1200 degrees C (AZO-2) in a flowing O2 gas environment. The stabilization (dwell) time has been fixed as 2 hours for all temperatures of firing in the furnace. After firing at 1200 degrees C, a new cubic phase (zinc aluminate) has been observed in the lattice along with the wurtzite ZnO phase. The microstructure analysis was substantiated with Rietveld refinement of the diffraction data of AZO-1 and AZO-2 samples. The photoluminescence (PL) measurements revealed that both AZO-1 and AZO-2 exhibited green (similar to 523 nm) PL under UV (375 nm) excitation, with emission intensity of AZO-1 comparatively higher than that of AZO-2 sample. Moreover, the measurement of electronic transport properties of the AZO-1 and AZO-2 samples exposed their n-type behavior, with slightly lower electrical resistivity of AZO-1 (4.7 x 10(-3)Omega-m) as compared to AZO-2 (3 x 10(-3)Omega-m) at 700 K temperature. The AZO samples have been used as target materials for transparent thin film deposition on quartz substrate, thus proving it to be ideal materials for solar cell applications