Shyam Bahadur Rai

Observation of intermediate bands in Eu3+ doped YPO4 host: Li+ ion effect and blue to pink light emitter

This article explores the tuning of blue to pink colour generation from Li+ ion co-doped YPO4:5Eu nanoparticles prepared by polyol method at ∼100-120 °C with ethylene glycol (EG) as a capping agent. Interaction of EG molecules capped on the surface of the nanoparticles and/or created oxygen vacancies induces formation of intermediate/mid gap bands in the host structure, which is supported by UV-Visible absorption data. Strong blue and pink colors can be observed in the cases of as-prepared and 500 °C annealed samples, respectively. Co-doping of Li+ enhances the emission intensities of intermediate band as well as Eu3+. On annealing as-prepared sample to 500 °C, the intermediate band emission intensity decreases, whereas Eu3+ emission intensity increases suggesting increase of extent of energy transfer from the intermediate band to Eu3+ on annealing. Emission intensity ratio of electric to magnetic dipole transitions of Eu3+ can be varied by changing excitation wavelength. The X-ray photoelectron spectrosc...

Magnetic-field-induced optical bistability in multifunctional Gd 2 O 3 :Er 3+ ∕Yb 3+ upconversion nanophosphor

The effect of an external magnetic field (0-1 T) on the upconversion emission (lambda(exc)=976 nm) of Gd(2)O(3):Er(3+)Yb(3+) nanocrystalline phosphor has been studied. Optical bistability (hysteresis behavior in the intensity of the optical emission) for different transitions of the Er(3+) ion has been observed for a complete cycle of the magnetic field between 0 and 1 T. The phosphor shows paramagnetic behavior, consistent with the presence of Gd(3+) ions, at room temperature. Interaction between induced magnetization in the Gd(2)O(3) host and the intrinsic magnetic moment of the nanosized clusters of Er(3+) and Yb(3+) ion pairs is proposed to be responsible for the hysteresis behavior.

Enhanced Red Upconversion Emission, Magnetoluminescent Behavior, and Bioimaging Application of NaSc0.75Er0.02Yb0.18Gd0.05F4@AuNPs Nanoparticles

The present study reports significant enhancement in the red upconversion emission of Er(3+) in NaSc0.8Er0.02Yb0.18F4 upconversion nanoparticles (UCNPs), via a two step process, (i) codoping of Gd(3+) ion at Sc(3+) site and (ii) attaching gold nanoparticles (AuNPs) at the surface of these codoped nanostructures, and further probes the use of these Gd:UCNPs@AuNPs for bioimaging application. The Gd(3+) codoping tailors the particle size (reduces) of UCNPs and bring out Er(3+)-Yb(3+) ion pair in close proximity, which promotes the cross relaxation mechanism and boosts the population in red emitting level (4)F9/2. Further, attachment of AuNPs on the surface of UCNPs gives 2-fold advantages, that is, reduction in green band (through resonance energy transfer with efficiency 31.54%) and enhancement in red band (through plasmonic effect). It gives red to green (R/G) ratio nearly 20:1 (almost single band red UC), which is quite promising for imaging application. In addition to this, codoping of Gd(3+) enhances the magnetic moment appreciably and the obtained magnetic moment for NaSc0.75Er0.02Yb0.18Gd0.05F4 UCNPs (∼1.7 emu/g) is close to the reported values for bioseparation in case of NPs. This shows the potential of the material for multimodal (optical and magnetic both) imaging application. These magnetoluminescence particles were found safe up to 1 mg/mL dose as assessed by cytotoxicity measurement in human cervical cancer (HeLa) and lung cancer (A549) cells. Ultrafine nanoparticles, transparent, and stable colloidal solution and the unique red UC emission endow these NPs as optical probe for imaging applications.

New Perspective in Garnet Phosphor: Low Temperature Synthesis, Nanostructures, and Observation of Multimodal Luminescence

Herein, we report a new concept for garnet materials in terms of the synthesis of nanocrystalline structure at low temperatures and its multimodal luminescence processes. Terbium- and ytterbium-ion-codoped yttrium gallium garnet nanophosphors have been synthesized via solution combustion technique; nearly pure phase nanophosphor samples were obtained. The synthesized nanophosphor shows efficient multimodal upconversion (UC), downshifting (DS), and quantum cutting (QC)/downconversion (DC) luminescence, which is a new paradigm in garnet material. The garnet nanophosphor shows strong green emission through DS and UC processes both. Furthermore, cooperative energy transfer (CET) has been described in detail, and a possible mechanism for the QC process is also proposed. A UV/blue photon absorbed by Tb(3+) ion splits into two near-infrared photons (wavelength range 900-1040 nm), emitted by a Yb(3+) ion pair, with an efficiency of more than 100%. The Yb(3+) concentration dependent ET from Tb(3+) to Yb(3+) has been verified using time domain analysis. An ET efficiency as high as 28% and a corresponding QC efficiency of about 128% (for 15 mol % of Yb(3+) concentration) have been attained. Such a multimode emitting nanophosphor could be very useful in display devices and for enhancing the conversion efficiency of next generation solar cells via spectral modification etc.

Effect of lead oxide on optical properties of Pr3+ doped some borate based glasses

Abstract The optical properties of Pr 3+ ions in some borate based glasses with varying concentration of lead oxide have been studied. The concentration of lead oxide has been varied from 0 to 50xa0mol%. The Judd–Ofelt intensity parameters ( Ω λ ) and other radiative properties for the glasses have been calculated. Variations of Judd–Ofelt intensity parameters are discussed on the basis of structural analysis. It is observed from fluorescence spectra that the fluorescence yield increases with addition of lead oxide and is about five times greater at 40% PbO than that at 0% PbO.

Host-Sensitized NIR Quantum Cutting Emission in Nd3+ Doped GdNbO4 Phosphors and Effect of Bi3+ Ion Codoping

Host-sensitized near-infrared quantum cutting (QC) emission has been demonstrated in Nd(3+) doped Gd(1-x)Nd(x)NbO4 phosphors for various x values. Further, the effect of Bi(3+) ion addition as a sensitizer on near-infrared QC is studied in detail. X-ray diffraction confirms a monoclinic structure for pure and Nd(3+) doped phosphors. Pulsed laser excitation at 266 nm of Gd(1-x)Nd(x)NbO4 and Gd(0.99-x)Nd(x)Bi(0.01)NbO4 causes efficient room-temperature energy transfer from the NbO4(3-) to the Nd(3+) ions and the NbO4(3-) and Bi(3+) ions to the Nd(3+) ions, respectively, which emits more than one near-infrared photon for single impinging ultraviolet photon. The emission band of Nd(3+) shows unusual character where the intensity of the (4)F(3/2)-(4)I(9/2) transition at 888 nm is higher than the intensity of the transition (4)F(3/2)-(4)I(11/2) at 1064 nm, due to energy transfer from GdNbO4 host to Nd(3+) ion. Using photoluminescence lifetime studies, the quantum cutting efficiencies are found to be the maximum 166% and 172% for Gd(0.95)Nd(0.05)NbO4 and Gd(0.94)Nd(0.05)Bi(0.01)NbO4, respectively. The present study could establish Nd(3+) ion as an alternative of Yb(3+) ion for near-infrared quantum cutting. This work facilitates the probing of Nd(3+) ions doped phosphor materials for next generation Si-solar cells.

Revelation of the Technological Versatility of the Eu(TTA)3Phen Complex by Demonstrating Energy Harvesting, Ultraviolet Light Detection, Temperature Sensing, and Laser Applications

We synthesized the Eu(TTA)3Phen complex and present herein a detailed study of its photophysics. The investigations encompass samples dispersed in poly(vinyl alcohol) and in ethanol in order to explore the versatile applicability of these lanthanide-based materials. Details upon the interaction between Eu, TTA, and the Phen ligands are revealed by Fourier transform infrared and UV-visible absorption, complemented by steady state and temporally resolved emission studies, which provide evidence of an efficient energy transfer from the organic ligands to the central Eu(3+) ion. The material produces efficient emission even under sunlight exposure, a feature pointing toward suitability for luminescent solar concentrators and UV light sensing, which is demonstrated for intensities as low as 200 nW/cm(2). The paper further promotes the complexs capability to be used as luminescence-based temperature sensor demonstrated by the considerable emission intensity changes of ∼4.0% per K in the temperature range of 50-305 K and ∼7% per K in the temeperature range 305-340 K. Finally, increasing the optical excitation causes both spontaneous emission amplification and emission peak narrowing in the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) - features indicative of stimulated emission. These findings in conjunction with the fairly large stimulated emission cross-section of 4.29 × 10(-20) cm(2) demonstrate that the Eu(TTA)3Phen complex dispersed in poly(vinyl alcohol) could be a very promising material choice for lanthanide-polymer based laser architectures.

A strategy to achieve efficient dual-mode luminescence in lanthanide-based magnetic hybrid nanostructure and its demonstration for the detection of latent fingerprints

We have synthesized a novel inorganic-organic hybrid nanostructure (IOHN) composed of fluoride nanophosphor (NaGd0.78Er0.02Yb0.2F4) and β-diketones complex (Eu(DBM)3Phen). The Le Bail fitting of X-ray diffraction data suggests that the nanophoshor crystallizes in a hexagonal structure (P63/m space group). The TEM studies reveal that the nanophosphor and the IOHN both have average particle size of 6-8nm. The Eu(DBM)3Phen and NaGd0.78Er0.02Yb0.2F4 show characteristic down-shifting (DS) and up-conversion (UC) emission, under UV and NIR excitation, respectively. The IOHN comprises an excellent dual-mode optical features (DS and UC) of both the phases. Energy transfer from Er3+ (doped in inorganic phase) to Eu3+ (coordinated in organic phase) clearly demonstrates for a viable coupling between both the phases. IOHN material was found to be unique for the visualization of latent fingermarks. Because of ultrafine particle size the surface to volume ratio is relatively higher which improves the attachment of particles with the fingermarks. On the other hand, the strong paramagnetic property helps to remove excess material with magnetic wand easily. These properties provide an opportunity to probe even very weak fingermarks. Notwithstanding this, the dual-mode emission is useful for the visualization of latent fingermarks on multi-color surfaces as well.

Effect of a chelating agent at different pH on the spectroscopic and structural properties of microwave derived hydroxyapatite nanoparticles: a bone mimetic material

In the present investigation, the effect of a capping agent (EDTA) and pH on the optical and structural characteristics of HAp nanoparticles (NPs) has been studied. Six samples of HAp were synthesized under six different chemical conditions. The HAp specimens were prepared via a microwave irradiation technique (MWIT) in the presence and absence of EDTA at three different pH values 9, 11 and 13. All the samples were calcined at 900 °C. HAp NPs with different sizes and shapes were found to be developed. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques were employed to determine the crystal structure, crystallite size and bonding parameters of the resulting HAp. The SEM measurements revealed the formation of the different morphologies of the HAp NPs under different physico-chemical conditions. Electron microscopies revealed that the particle size of the samples was in the range of ∼10–200 nm. The TEM results were in good agreement with the SEM results. The study revealed the vital role of the chelating agent (EDTA) in the formation of the pure phase HAp nanostructures. EDTA assisted the formation of needle-like nanorods of HAP and prevented agglomeration. EDTA also prevented carbonate impurities. Carbonate impurities, probably from the atmosphere, were observed in the HAp samples formed without EDTA. Despite the effect of EDTA, the pH of the solution also played a key role in deciding the final morphology of the HAp nanostructures. The samples were also characterized spectroscopically using Fourier transform infrared (FT-IR) spectroscopy and Raman techniques to understand the molecular interactions. The application of laser induced breakdown spectroscopy (LIBS) detected the presence of N and further confirmed the formation of the HAp powders.

On the correlation between the thermal and electrical transport in ionic conductors

Simultaneous measurements of the thermal diffusivity and electrical conductivity of some ion conducting polymer–solid and solid–solid composites have led us to establish, for the first time, a correlation between these quantities in ionic conductors similar to the Wiedmann–Franz law applicable to electron conducting metals according to which the ratio of thermal to electrical conductivity is almost constant. However, the proportionality constants for the ionic conductors are found to be different for systems with (a) different mobile species, namely H+, Li+ or Ag+ and/or (b) different morphology, i.e. polymeric or polycrystalline.