Variation of the photoluminescence and vacuum ultraviolet excitation characteristics of BaZr(BO3)2:Eu3+ by the incorporation of Al3+, La3+, or Y3+ into the lattice

The photoluminescence (PL) and vacuum ultraviolet (VUV) excitation properties are studied for the BaZr(BO₃)₂:Eu³⁺ phosphor with incorporating the Al³⁺, La³⁺, or Y³⁺ ion into the lattice. The excitation spectrum shows an absorption band in the VUV region with the band-edge at 200 nm and a very weak charge transfer band of Eu³⁺ at about 226 nm. The luminescence spectrum shows a strong emission at 615 nm (⁵D₀ → ⁷F₂ transition) and weak emission at 594 nm (⁵D₀ → ⁷F₁ transition) in BaZr(BO₃)₂:Eu³⁺, with a good red color purity. The PL intensity is increased by incorporating Al³⁺ into the BaZr(BO₃)₂ lattice. The PL intensity has also increased by incorporating La³⁺ into the lattice, however, the red color purity has deteriorated because of the increased centrosymmetric nature of the site. With the incorporation of Y³⁺ into the BaZr(BO₃)₂ lattice, the PL characteristics of the Eu³⁺ activator resembles that in the YBO₃ lattices. The intensity of the red PL for the Eu³⁺ activator is the highest with good color purity for BaZr(BO₃)₂:Eu³⁺ incorporated with both Al³⁺ (10%) and La³⁺ (0.5%).     

Multicolor Emission in a Single‐Phase Phosphor Ca3Al2O6:Ce3+,Li+: Luminescence and Site Occupancy

A single‐phase multicolor emitting phosphor, Ca₃Al₂O₆:Ce³⁺,Li⁺, was prepared by a solid‐state reaction. When the Ce³⁺ concentration is lower than 0.030 (molar ratio in Ca₃Al₂O₆), yellow and greenish blue emissions can be observed under the excitation by a blue and a near UV light, respectively. The yellow‐emitting phosphor possesses an internal quantum efficiency of 89%. Additional purplish blue emission turns up when Ce³⁺ concentrations are higher than 0.040. Tunable emission bands are originated from Ce³⁺ ions on different Ca sites in Ca₃Al₂O₆. Although the emission band of purplish blue or greenish blue overlaps the excitation band of yellow emission, and the distances between the unlike Ce³⁺ ions are in the range of electric dipole–dipole interaction, no energy transfer is observed. Furthermore, emission wavelengths for the yellow, greenish blue, and purplish blue emission show little change upon increasing Ce³⁺ concentrations.     

Visible light cleavage of water by CdS photoanode coated with polymer-pendant Ru(bpy)2+3 film containing RuO2 dispersions

Simultaneous formation of H₂ and O₂ by visible light cleavage of water was achieved using n-CdS photoanode coated with polymer-pendant Ru(bpy)²⁺₃ film containing RuO₂ dispersions. The Ru complex worked as a relay to transport the holes formed on the CdS surface to the RuO₂ catalyst where water oxidation takes place.     

Effect of Yb3+ concentration on the green-yellow upconversion emission of SrGe4O9:Er3+ phosphors

This work presents the structural, morphological and luminescent, properties of SrGe₄O₉ (SGO):Er³⁺,Yb³⁺ phosphors. These phosphors were synthesized by simple combustion synthesis and subsequently annealed at 1100 °C. The XRD patterns revealed that all the SGO samples doped with Yb³⁺ concentrations from 2 to 10 at.% presented a trigonal pure phase (the Er³⁺ concentration was fixed to 1 at.%). The morphology of the SGO samples was analyzed by scanning electron microscopy and found that they are formed by microparticles with irregular shapes and average sizes in the range of 0.2 μm–3 μm. The luminescence measurements of the SGO:Er³⁺,Yb³⁺ samples showed the presence of two main emission bands at 551 nm (green) and at 662 nm (red) under excitation at 980 nm, which are associated to Er³⁺ transitions. For Yb concentration of 2 and 3 at.% the green band dominated, but the red band became more intense for Yb concentrations above 5 at.%. As result, the CIE coordinate changed from the green to the yellow region. The increase for the Yb content from 2 to 10 at.% also enhanced of the NIR emission of Er³⁺ ≈5 times and the maximum upconversion emission was observed for 8% of Yb concentration. Further, the surface of the SGO samples was analyzed by the FTIR technique in order to find OH groups which are common luminescent quenching centers, but these groups were not detected on the samples. Since the SGO samples presented tunable emission, absence of OH groups on their surface and stable crystalline structure for high Yb dopant concentrations, they could be good candidates as phosphors for solid state lighting or displays applications.     

Impact of grain size,Pr~(3+) concentration and host composition on non-contact temperature sensing abilities of polyphosphate nano- and microcrystals

In this article,varied praseodymium polyphosphate hosts:M~I(Li,Na K)Pr(PO_3)_4 microcrystals and LiLa_(1-x)Pr_x(PO_3)_4(x = 0.01-1)nanocrystals were successfully synthesized by the flux method and the coprecipitation technique,respectively.The size of stoichiometric nanocrystals of LiPr(PO_3)_4 was tuned by the te mpe rature of thermal treatment in range of 35-145 nm.In order to dete rmine the most suitable material for the non-contact optical thermometric applications,the temperature sensing measurements were carried out by using luminescence intensity ratio(LIR)of emission bands corresponding to the ~3 P_1→~3H_5 and ~3P_0→~3 H_5 electronic transitions of Pr~(3+) ions into the 123-423 K temperature range.The influence of the host material composition of M~Ⅰ(Li,Na,K)Pr(PO_3)_4 microcrystals on the sensitivity of luminescent thermometers was studied.It is found that the sensitivity of lithium praseodymium polyphosphate is the highest of all micropowders under investigation.Moreover,it is found that the nanocrystals reveal much higher relative sensitivity in respect to the microcrystalline counterparts.The highest sensitivity of LIR temperature sensing is found for LiPr(PO_3)_4 nanocrystals(35 nm grain size)in the whole temperature range,reaching 0.283%/K at 164 K.The impact of the average grain size on the sensitivity of LIR based thermometers of LiPr(PO_3)_4 nanocrystals was investigated.It is found that the reduction of the grain size from 145 to 35 nm results in the enhancement of the relative sensitivity from0.156 to 0.240%/K at 223 K.Additionally it is found that the high dopant concentration possesses favorable influence on the relative sensitivity of LiLa_(1-x)Pr_x(PO_3)_4 nanocrystalline luminescent thermometers.     

Preparation of Pt/multiwalled carbon nanotubes modified Au electrodes via Pt–Cu co-electrodeposition/Cu stripping protocol for high-performance electrocatalytic oxidation of methanol

Pt nanoparticles well dispersed on multiwalled carbon nanotubes (MWCNTs) were prepared for high-performance electrocatalytic oxidation of methanol in both acidic and alkaline media via the co-electrodeposition/stripping (CS) protocol, namely, co-electrodeposition of Pt and Cu followed by electrochemical stripping of Cu, as examined by cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The Pt catalyst prepared by the CS protocol on MWCNTs (Pt_cs/MWCNTs/Au) exhibited a specific electrocatalytic activity of 519 and 2210 A g⁻¹ toward cyclic voltammetric electrooxidation (50 mV s⁻¹) of methanol in 0.5 M CH₃OH + 0.5 M H₂SO₄ and 0.5 M CH₃OH + 1.0 M NaOH media, respectively, which are larger than those prepared by conventional electrodeposition from chloroplatinic acid on Au and MWCNTs/Au, as well as that by a CS protocol on Au. The Pt_cs/MWCNTs/Au electrode also possessed the highest stability, which maintained 91% and 90% of its initial catalytic activity after 120-cycle CV in 0.5 M CH₃OH + 0.5 M H₂SO₄ and 0.5 M CH₃OH + 1.0 M NaOH, respectively. The electrode kinetics of methanol oxidation is also briefly discussed. The nanosubstrate-based CS protocol is simple, convenient and efficient, which is expected to find wide applications in film electrochemistry and electrocatalysis.     

Hydrothermal-assisted synthesis of surface aluminum-doped LiCoO2 nanobricks for high-rate lithium-ion batteries

LiCoO₂ nano-particles precursor was synthesized through a mixed-alkalis (LiOH-NaOH) hydrothermal reaction, and finally sintered into LiCoO₂ nanobricks with a sickness of ~300?nm. This LiCoO₂ nanobrick cathode delivered a specific capacity of 131.8 mAh g^?1 at 1?C between 3.0 and 4.2?V and 90% capacity retention after 100 cycles. Those synthesized LiCoO₂ nanobricks were further treated by surface Al³⁺ doping to achieve much enhanced 4.5?V lithium storage capability and cycling stability. EIS results showed the surface Al³⁺ doping operation can signification decrease the charge-transfer resistances of the LiCoO₂ cathodes for both before and after cyclings.     

Preparation and properties of an uricase biosensor based on copolymer of o-aminophenol-aniline

An uricase biosensor of poly-o-aminophenol-aniline is firstly reported in this paper. The preparing process of the biosensor is as follows: An uricase electrode is prepared with one-step process using the copolymer of aniline and o-aminophenol, then the electrode is hydrolyzed in 6.0 mol dm⁻³ hydrochloric acid solution to remove the uricase that may be affected by monomer during copolymerization and a template with moderate apertures for immobilization uricase was obtained. Finally, active uricase is immobilized into the template based on doping and undoping of the copolymer, and a copolymer-uricase biosensor is obtained. Some factors that affect response current are studied, such as temperature, pH, potential and substrate concentration. The result of experiment indicates that the response current of the copolymer-uricase biosensor prepared with template process only decreases by about 19% for 50 days, but that of polyaniline-uricase biosensor prepared with two-step process decreases by approximately 43% for 40 h. FTIR, UV–vis and SEM are used to characterize the copolymer-uricase biosensor.     

Enhanced emission and improved thermal stability of BaMgAl10O17:Eu2+ phosphor via additional Mg2+ doping

BaMgAl₁₀O₁₇:Eu²⁺ doped with 0–6% additional Mg²⁺ were synthesized by co-precipitation method. Their photoluminescence and thermal stability were investigated under ultraviolet (UV) and vacuum ultraviolet (VUV) excitation. The additional Mg²⁺-doped samples exhibited stronger emission intensity and better thermal stability than the sample without additional Mg²⁺ under 254 or 147 nm excitation. After thermal degradation, the 4% additional Mg²⁺-doped sample had the highest emission intensity which was 12.7% and 16.6% stronger than that of the sample without additional Mg²⁺ under 254 and 147 nm excitation, respectively. Moreover, the improvement mechanisms on emission intensity and thermal stability were discussed.