[en] Highlights: • Eu"3"+ ions occupy C_1 point group of the Zr"4"+ site in ZrW_2O_8 crystals. • The optimum doping concentration of Eu"3"+ was determined for the red emission. • ZrW_2O_8:Eu possess high quantum efficiency and suitable chromaticity coordinates. - Abstract: ZrW_2O_8:Eu"3"+ nanophosphors (ca. 60 nm) with different Eu"3"+ doping concentrations were obtained using hydrothermal syntheses. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence excitation and emission spectra as well as decay curve measurements were used for the characterization. Under 466 nm excitation, strong red emission at 616 nm corresponding to "5D_0–"7F_2 transition of Eu"3"+ was observed for ZrW_2O_8:Eu"3"+ (9 mol%) phosphors. The values of intensity parameter Ω_2 and Ω_4 are 17.82 × 10"−"2"0 cm"2 and 1.092 × 10"−"2"0 cm"2, respectively. The high quantum efficiency of 83.5% of the ZrW_2O_8:Eu"3"+ (9 mol%) suggests this material could be promising red phosphor for generating white light in phosphor-converted white light-emitting diodes (LED)

[en] Eu³⁺-Yb³⁺-Y³⁺ tri-doped cubic ZrO₂ (abbreviated as YSZ:Eu,Yb) phosphors with different doping concentrations of Yb³⁺ can be synthesized via the Pechini sol-gel method. Efficient near-infrared (NIR) emission in YSZ:Eu,Yb phosphors was demonstrated. The dependence of the intensities of visible and NIR emissions, decay lifetimes and energy-transfer efficiencies on the Yb³⁺ doping concentration was investigated in detail. It is found that Eu³⁺, acting as a sensitizer, can efficiently transfer its energy to Yb³⁺ activator ions in YSZ:Eu,Yb phosphors

[en] Pyrochlore Gd₂Sn₂O₇:Eu³⁺ (in brief GSO:Eu) nanoparticles have been prepared by the microwave hydrothermal method followed by further calcining treatment. The effects of pH value and Eu³⁺-doping concentration on the pure phase of the products are investigated. It is found that the pH value is a crucial step for the control of the pure phase of the GSO nanocrystals. All the products were systematically characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectra (EDS), photoluminescence (PL) spectra and decay curve. Under the 391 nm excitation, intense reddish orange emission peak at 587 nm corresponding to ⁵D₀→⁷F₁ transition of Eu³⁺ is observed for 7 mol% GSO:Eu phosphor as the optimal doping concentration. The luminescence property indicates that the local symmetry of Eu³⁺ ion in GSO crystal lattice has inversion center of Gd³⁺ ion with D_3d point group. The luminescence properties suggest that a brightly luminescent GSO:Eu phosphor with reddish orange light may be considered as an ideal optical material for the development of new optical display systems.

[en] Yb³⁺ and Er³⁺ co-doped Y₂Ce₂O₇ nanoparticles sintered at different temperatures were prepared by homogeneous co-precipitation method. The products were characterized by X-ray powder diffraction (XRD), energy-dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The results indicated that the particle sizes and morphologies of the samples were heavily influenced by the sintering temperature. As temperature increased, the particle sizes became gradually larger and more agglomerate. The emissions including green and red upconversion emissions were investigated under 980 nm excitation. The emission intensities of the samples also depended on the sintering temperature. Two photon processes were mainly responsible for green and red upconversion emissions. (author)

[en] The authors describe the synthesis, characterization and electrochemical sensing performance of a PrFeO₃-MoS₂ nanocomposite. Graphene-like MoS₂ sheets and a perovskite-type PrFeO₃ were synthesized via a hydrothermal and a sol-gel method, respectively. Finally, PrFeO₃-MoS₂ nansheets were synthesized by using sodium molybdate as a source for molybdenum and thiourea as the source for sulfur. The nansheets were characterized by transmission electron microscopy and X-ray diffraction. The electrochemical behavior of the nanosheets deposited on a glassy carbon electrode was studied via electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrodes display strong response to nitrite. At a scan rate of 100 mV·s⁻¹, the current at the oxidation peak at 0.85 V (vs. SCE) increases linearly in the 0.005 to 3 mM nitrite concentration range. The detection limit is 1.67 μmol·L⁻¹ (S/N = 3). The sensor is selective, stable and reproducible. It was successfully applied to the determination of nitrite in (spiked) real samples, and appropriate recoveries were obtained. .

[en] Er³⁺ doped and Yb³⁺/Er³⁺ co-doped Y₄Al₂O₉ phosphors are prepared by the sol-gel method. The effect of dopant concentration on the structure and up-conversion properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to monoclinic. Under 980 nm excitation, the green and red up-conversion emissions are observed and the emission intensities depended on the Yb³⁺ ion concentration. The green up-conversion emissions decrease with the increase of Yb³⁺ concentration, while red emission increases as Yb³⁺ concentration increases from 0 to 8 at% and then decreases at high Yb³⁺ concentration. The mechanisms of the up-conversion emissions are discussed and results shows that in Er³⁺ and Yb³⁺/Er³⁺ co-doped system, cross-relaxation (CR) and energy transfer (ET) processes play an important role for the green and red up-conversion emissions.

[en] Multiwavelength near infrared emission of Tm³⁺ in double perovskite Y₂MgTiO₆:Mn⁴⁺/Tm³⁺ (in brief YMT: Mn⁴⁺/Tm³⁺) phosphors is to easily achieve by resonance energy transfer and downshift (or downconversion) between rare earth ions and transition metal ions. In this study, we observe the multiwavelength near infrared emissions of Tm³⁺ in Mn⁴⁺-Tm³⁺ co-doped YMT phosphors synthesized by a high temperature solid-state reaction. During the resonance energy transfer from Mn⁴⁺ to Tm³⁺, the YMT:Mn⁴⁺/Tm³⁺ phosphor exhibits three wavelength near-infrared emission around 800, 1488 and 1800 nm originating in ³H₄→³H₆, ³H₄→³F₄ and ³F₄→³H₆ of Tm³⁺ with a wide excitation band extending from 250 to 550 nm. The cascade emission of two wavelengths (1488 and 1800 nm) is mainly contributed to downconversion of Tm³⁺ ions. Based on Dexter's theory, the energy transfer mechanism is mainly contributed to a dipole-dipole interaction between Mn⁴⁺ and Tm³⁺ ions, which is responsible for the largely enhanced multiwavelength near infrared emission of Tm³⁺. Multiwavelength near infrared emission of Tm³⁺ make them potential application in solid state lasers, bioimaging, Ge photovoltaic devices (band gap approximately 0.67 eV) and so on.

[en] Highlights: • A novel far-red/green dual-emitting phosphor was synthesized by sol-gel method. • The relative intensity of far-red/green can be controlled by changing temperature. • The quadrupole-quadrupole interaction was mainly responsible for energy transfer. A new far-red/green dual-emitting phosphor La₂ZnTiO₆:Mn⁴⁺/Er³⁺ (LZT:Mn⁴⁺/Er³⁺) was successfully synthesized by the sol-gel method. Under 381​nm excitation, LZT:Mn⁴⁺/Er³⁺ phosphor shows the strong far-red emission peak of 709​nm (Mn⁴⁺: ²E_g→⁴A_2g) and weak green emission peak of 523/548​nm (Er³⁺: ²H_11/2/⁴S_3/2​→​⁴I_15/2), which consistent with the requirement of plant growth for far-red and green light. A 1.5-fold enhancement of far-red emission intensity is found in LZT:Mn⁴⁺/Er³⁺ phosphor compared with the Mn⁴⁺ singly-doped counterparts. Moreover, the relative emission intensity of far-red and green can be easily controlled by changing temperature. Utilizing the optimal LZT:0.2%Mn⁴⁺/2%Er³⁺ phosphor as plant lighting, a prototype near-UV-pumped LED device was fabricated. Upon 120​mA driving current, it demonstrated far-red/green dual emission. All the results indicated that the LZT:Mn⁴⁺/Er³⁺ phosphor is a potential material for plant growth illumination with far-red/green light.

[en] A nanocomposite is described that consists of TmPO₄ and graphene oxide (GO) and is used to modify a glassy carbon electrode (GCE) to obtain a sensor for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). GO and TmPO₄ were synthesized via the Hummers method and by a hydrothermal method, respectively. The nanocomposite was characterized by transmission electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction and Fourier transform infrared spectroscopy. The electrochemical properties of the modified GCE were studied by electrochemical impedance spectroscopy and cyclic voltammetry. The good performance of the modified GCE results from the synergistic effects between GO with its good electrical conductivity and of TmPO₄ as the electron mediator that accelerates the electron transfer rate. Compared to a bare GCE, a GO/GCE and a TmPO₄/GCE, the GO/TmPO₄/GCE exhibits three well-defined and separated oxidation peaks (at −0.05, +0.13 and + 0.26 V vs. SCE). Responses to AA, DA and UA are linear in the 0.1–1.0 mM, 2–20 μM and 10–100 μM concentration ranges, respectively.

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[en] Tetragonal $\text{NaY}({\text{MoO}}_4{)}_2$ (NYM) phosphors co-doped with ${\text{Yb}}^{3+}$ and ${\text{Tm}}^{3+}$ ions were synthesized through microwave hydrothermal method followed by calcining treatment. Powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and photoluminescence spectra were used to characterize the properties of as-prepared samples. The results show that ${\text{Yb}}^{3+}$/${\text{Tm}}^{3+}$ co-doped NYM displayed bright blue emission near 472 and 476 nm (${}^1{\text{G}}_4\to <!--\; ???\; -->{}^3{\text{H}}_6$ transition), strong near-infrared upconversion (UC) emission around 795 nm (${}^3{\text{H}}_4\to <!--\; ???\; -->{}^3{\text{H}}_6$ transition). The optimum doping concentrations of ${\text{Yb}}^{3+}$ and ${\text{Tm}}^{3+}$ for the most intense UC luminescence were obtained, and the related UC mechanism of ${\text{Yb}}^{3+}$/${\text{Tm}}^{3+}$ co-doped NYM depending on pump power was studied in detail.