Optimization of sensitizer concentration for upconversion photoluminescence of Yb3+/Er3+: La10W22O81 nanophosphor rods

Yb³⁺/Er³⁺codoped La₁₀W₂₂O₈₁ (LWO) nanophosphor rods have been successfully synthesized by a facile hydrothermal assisted solid state reaction method, and their upconversion photoluminescence properties were systematically studied. X-ray diffraction patterns revealed that the nanophosphors have an orthorhombic structure with space group Pbcn (60). A microflowers-like morphology with irregular hexagonal nanorods was observed using field emission scanning electron microscopy for the Yb³⁺(2 mol%)/Er³⁺(2 mol%):LWO nanophosphor. The shape and size of the nanophosphor and the elements along with their ionic states in the material were confirmed by TEM and XPS studies, respectively. A green upconversion emission was observed in the Er³⁺: LWO nanophosphors under 980 nm laser excitation. A significant improvement in upconversion emission has been observed in the Er³⁺: LWO nanophosphors by increasing the Er³⁺ ion concentration. A decrease in the upconversion emission occurred due to concentration quenching when the doping concentration of Er³⁺ ions was greater than 2 mol%. An optimized Er³⁺(2 mol%): LWO nanophosphor exhibited a strong near infrared emission at 1.53 μm by 980 nm excitation. The green upconversion emission of Er³⁺(2 mol%): LWO was remarkably enhanced by co-doping with Yb³⁺ ions under 980 nm excitation because of energy transfer from Yb³⁺ to Er³⁺. The naked eye observed this upconversion emission when co-doping with 2 mol% Yb³⁺. In order to obtain the high upconversion green emission, the optimized sensitizer concentration of Yb³⁺ ions was found to be 2 mol%. The upconversion emission trends were studied as a function of stimulating laser power for an optimized sample. Moreover, the NIR emission intensity has also been enhanced by co-doping with Yb³⁺ ions due to energy transfer from Yb³⁺ to Er³⁺. The energy transfer dynamics were systematically elucidated by energy level scheme. Colorimetric coordinates were determined for Er³⁺ and Yb³⁺/Er³⁺: LWO nanophosphors. The energy transfer mechanism was well explained and substantiated by several fluorescence dynamics of upconversion emission spectra and CIE coordinates. The results demonstrated that the co-doped Yb³⁺(2 mol%)/Er³⁺(2 mol%): LWO nanophosphor material is found to be a suitable candidate for the novel upconversion photonic devices.     

Stabilization of 6H-Hexagonal SrMnO3 Polymorph by Al2O3 insertion

We demonstrate the structural evolution of polymorphic phases in Al₂O₃-inserted SrMnO₃ ceramics synthesized by solid state reaction. While the 4H-hexagonal phase is predominant in pure SrMnO₃ ceramics, a small amount of 6H-hexagonal polymorph is identified in addition to the primary 4H-hexagonal SrMnO₃ and the secondary hexagonal SrAl₂O₄ phases in the as-sintered ceramics, evidenced by x-ray diffraction and subsequent Rietveld refinement analyses. The existence of the 6H-hexagonal SrMnO₃ phase is corroborated using Raman spectroscopy. The chemical compositions and electronic structures of the Al₂O₃-inserted SrMnO₃ compounds are also examined using energy dispersive spectroscopy and x-ray photoelectron spectroscopy, respectively. The first-principles calculations reveal that there is no clear difference between the total energies of 4H- and 6H-hexagonal polymorphs regardless of the presence/absence of Sr and oxygen vacancies. Possible origins are discussed with the estimation of actual strain based on the refined lattice parameter of 6H SrMnO₃.     

Brief Review of Precipitated Iron-Based Catalysts for Low-Temperature Fischer–Tropsch Synthesis

Topics in Catalysis - Fischer–Tropsch synthesis (FTS) is a promising way to produce clean liquid fuels and high value-added chemicals from low-value carbon-containing resources such as coal,...     

Analyzing the Variability in Low-Flow Projections under GCM CMIP5 Scenarios

Water Resources Management - The present study considered the impacts of global climate model (GCM) selection in the Couple Model Intercomparison Phase 5 (CMIP5) scenarios on the low-flow...     

Gait event detection algorithm based on smart insoles

Gait analysis is an effective clinical tool across a wide range of applications. Recently, inertial measurement units have been extensively utilized for gait analysis. Effective gait analyses require good estimates of heel‐strike and toe‐off events. Previous studies have focused on the effective device position and type of triaxis direction to detect gait events. This study proposes an effective heel‐strike and toe‐off detection algorithm using a smart insole with inertial measurement units. This method detects heel‐strike and toe‐off events through a time‐frequency analysis by limiting the range. To assess its performance, gait data for seven healthy male subjects during walking and running were acquired. The proposed heel‐strike and toe‐off detection algorithm yielded the largest error of 0.03 seconds for running toe‐off events, and an average of 0–0.01 seconds for other gait tests. Novel gait analyses could be conducted without suffering from space limitations because gait parameters such as the cadence, stance phase time, swing phase time, single‐support time, and double‐support time can all be estimated using the proposed heel‐strike and toe‐off detection algorithm.     

Multimedia content recommendation in social networks using mood tags and synonyms

Multimedia Systems - The preferences of Web information purchasers are changing. Cost-effectiveness (i.e., an emphasis on performance with respect to price) is becoming less regarded than...     

Mechanistic insight into gold nanorod transformation in nanoscale confinement of ZIF-8

Core-shell hybrid nanomaterials have shown new properties and functions that are not attainable by their single counterparts.Nanoscale confinement effect by porous inorganic shells in the hybrid nanostructures plays an important role for chemical transformation of the core nanoparticles.However,metal-organic frameworks(MOFs)have been rarely applied for understanding mechanical insight into such nanoscale phenomena in confinement,although MOFs would provide a variety of properties for the confining environment than other inorganic shells such as silica and zeolite.Here,we examine chemical transformation of a gold nanorod core enclosed by a zeolitic imidazolate framework(ZIF)through chemical etching and regrowth,followed by quantitative analysis in the core dimension and curvature.We find the nanorod core shows template-effective behavior in its morphological transformation.In the etching event,the nanorod core is spherically carved from its tips.The regrowth on the spherically etched core inside the ZIF gives rise toformation of a raspberry-like branched nanostructure in contrast to the growth of an octahedral shape in bulk condition.We attribute the shell-directed regrowth to void space generated at the interfaces between the etched core and the ZIF shell,intercrystalline gaps in mult-domain ZIF shells,and local structural deformation from the acidic reaction conditions.