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(Lu, Gd)2O3: Ce3+, Tb3+ phosphors with different Ce3+ and Tb3+ contents were prepared by sol–gel method using citric acid as a chelating agent. The effects of Ce3+/Tb3+ doping concentration on the crystal structure and photo-/cathodo-luminescence properties of the phosphors were investigated. The X-ray diffraction analysis of the samples shows that the synthesized phosphors are well-crystallized and display a pure Lu2O3 phase, indicating the successful formation of (Lu, Gd)2O3 solid solution host. The phosphors show approximately spherical morphology, uniform distribution of particle size and elements. Upon the excitation of ultra-violet light, the photoluminescence spectra of the phosphors with different Ce3+ doping concentrations consist of four emission peaks, which correspond to the 5D4 → 7FJ (J = 6, 5, 4, and 3) transitions of Tb3+ ions, respectively. The photoluminescence spectra of the phosphors with different Tb3+ doping concentrations consist of five emission peaks, which correspond to the 5D3 → 7F4 and 5D4 → 7FJ (J = 6, 5, 4, and 3) transitions of Tb3+ ions, respectively. Upon the excitation of cathode ray, the (Lu, Gd)2O3: Ce3+, Tb3+ phosphors exhibit luminescence spectra similar to that of the samples excited by ultra-violet light and a color-tunable luminescence property. In addition, the energy transfer mechanism between Ce3+ and Tb3+ ion is also discussed. [ABSTRACT FROM AUTHOR]

Yttrium aluminum garnet (Y3Al5O12, YAG) ceramics with a relative density of about 99.5% were fabricated by solid-state reaction and pressureless sintering using commercial α-Al2O3 and Y2O3 powders as raw materials in air. The effect of different sintering additives, e.g. tetraethyl orthosilicate (TEOS), MgO and TEOS + MgO, on the relative density and mechanical properties of the YAG ceramic samples were investigated. When the dopant content of TEOS exceeded 0.5 wt.%, a sudden grain growth appeared, as well as a residual second phase located in triangle grain boundary. MgO was more effective as a sintering additive than silica in promoting the densification of the YAG ceramics. The relative density of the ceramics gradually decreased with the increase of MgO doping content and fixed TEOS content. The mechanical properties of the YAG ceramics fabricated by pressureless sintering in air at 1600-1710°C were tested. The fracture surface morphology of the MgO-doped ceramic samples was mainly transgranular, whereas the TEOS-doped samples were mainly intergranular. [ABSTRACT FROM AUTHOR]

YVO4:Bi3+,Ln3+ (Ln = Dy, Sm, Eu) phosphors were successful synthesized by microwave sintering method, and characterized by X-ray powder diffraction, scanning electron microscope, photoluminescence spectra, lifetime, quantum efficiency and general structure analysis system structure refinement. Refinement results indicated that the introduced ions occupy the sites of Y3+. Under 275 nm excitation, the luminescent intensity of YVO4:Bi3+ samples reach the maximum when Bi3+ concentration is 0.02, the broad excitation spectrum of YVO4:Bi3+ has a strongest peak at near 343 nm. Doped Bi3+ can effectively improve the emission intensity of YVO4:Ln3+. The energy transfer mechanism of Bi3+ → Ln3+ was dipole-quadrupole mechanism of electric multipole interaction. The critical distance (Rc) between Ln3+ and Bi3+ were calculated by concentration quenching method. Emitting color of YVO4:Bi3+,Ln3+ phosphors were tunable by adjusting Ln3+ content. In a word, the material has a good application prospects on light emitting diodes. [ABSTRACT FROM AUTHOR]

Well-crystallized NaREF4: Yb3+, Er3+ (RE = Y, Lu, La, Gd) phosphors were synthesized by a solid-state reaction method. X-ray diffraction characterization showed that the synthesized samples were all pure hexagonal phase after a calcination process on the as-prepared precursors at 550 °C for 2 h by using Na2CO3 as a fluxing agent. Upconversion spectral analysis showed that under a 1550 nm laser diode excitation, the samples emitted dominant green emission centered at 540 nm and red emission centered at 654 nm, which corresponded to the 2H11/2/4S3/2→4I15/2 and 4F9/2→4I15/2 transition of Er3+ ions, respectively. Color-tunable upconversion luminescence was realized by the variation of Yb3+/Er3+ doping concentration and the types of the host materials, indicating the synthesized hexagonal Yb3+ and Er3+ co-doped NaREF4 phosphors potential applications in many fields, especially in biological imaging and detection. [ABSTRACT FROM AUTHOR]

Y 2 O 3 :Yb3+, Er3+, Eu3+ phosphors with different Yb3+, Er3+ and Eu3+ doping concentrations were prepared by sol-gel method using glycine as a chelating agent. The effect of Yb3+/Er3+/Eu3+ doping concentrations on the upconversion and near-infrared spectral performances of the synthesized phosphors were investigated. The XRD analysis shows that the samples calcined at 1000 °C for 2 h are well-crystallized and show a pure cubic Y 2 O 3 phase. Upon excitation of 980 nm excitation source, the emission intensity of green/red upconversion and 1.54 μm near-infrared emission of the samples can be adjusted with the variation of Eu3+ doping concentrations. The samples also display a color-tunable upconversion emission with the variation of Eu3+ doping concentration and the excitation power of 980 nm laser diode. In addition, the energy transfer mechanism among Yb3+, Er3+ and Eu3+ in upconversion and 1.54 μm emission processes are also discussed. • Sol-gel synthesis of Y 2 O 3 :Yb3+, Er3+, Eu3+ phosphors. • 980 nm LD excited color-tunable upconversion luminescence. • Eu3+ doping can apparently enhance the 1.54 μm NIR emission intensity of the samples. • Applications in optical communications, eye-safe laser, display devices, solar cells. [ABSTRACT FROM AUTHOR]

Well-crystalline β-NaYF:Yb, Ho, Tm nanoparticles were synthesized by sol-gel method using isopropyl alcohol [(CH)CHOH] as a complexing agent. The samples were characterized by X-ray diffraction, scanning electron microscopic analysis and fluorescence spectrum analysis methods. Under the excitation of 980 nm laser diode (LD), the samples displayed bright upconversion luminescence (UCL), which was generated from the energy level transition of Ho and Tm ions. With the increase of Tm, Ho and Yb-doping concentration, the UCL intensity of blue, green and red light emission of the samples varied. Calculation of the CIE color coordinate of the β-NaYF:Yb, Ho, Tm nanoparticles revealed that with the adjustment of Tm, Ho and Yb doping concentration and the excitation power of 980 nm LD, the multi-color UCL can be realized. Approximately single red light output with the CIE color coordinate of x = 0.545, y = 0.306 and white light output with the CIE color coordinate of x = 0.325, y = 0.320 can be obtained in the synthesized β-NaYF: Yb, Ho, Tm nanoparticles. [ABSTRACT FROM AUTHOR]

Novel broadband luminescence phosphors CaNaMgVO:xEu have been successfully prepared via the conventional high-temperature solid-state reaction. The effects of concentrations of doped Eu and introducing Li, K on the luminescent properties of phosphor were studied. X-ray diffraction, GSAS structural refinement and photoluminescence spectra were used to characterize the samples. The refinement data ensured where the doped Eu ions occupied the lattice site in the host. Under 355 nm excitation, the emission peak of CaNaMgVO:Eu phosphors are located at 610 nm (red) ascribed to the electric dipole transition of Eu from D → F. In the range of 400-575 nm, CaNaMgVO:Eu phosphors have broad emission bands attributed to charge transfer of $${\text{VO}}_4^{3 - }$$ group. Energy transfer mechanism, energy transfer efficiency and critical distance (R) of $${\text{VO}}_4^{3 - }$$ → Eu would be analyzed. The emitting color of CaNaMgVO:Eu could be tunable from blue-green to near white light. [ABSTRACT FROM AUTHOR]

Abstract: Highly transparent Er3+/Yb3+ co-doped yttria ceramics were fabricated by a solid-state reaction method using high purity Y2O3, Er2O3 and Yb2O3 powders as starting materials and La2O3 as an additive. The microstructure evolution and optical properties of the ceramics were investigated. Fully dense Y2O3: Er3+, Yb3+ ceramics with mean grain size of about 60 μm were obtained by vacuum sintering at 1800 °C for 10 h. The highest transmittance of the ceramic sample is more than 75% in the range from 500 to 3000 nm. Under the 980 nm laser diode excitation, the ceramic sample exhibits intense up-conversion luminescence, which is centered at 561 and 662 nm respectively. [Copyright &y& Elsevier]

Abstract: Ytterbium-doped yttria (Yb3+:Y2O3) nanopowders for transparent ceramics were synthesized by using a carbonate-precipitation method. The characteristics of precursor and powders calcined at different temperatures were investigated. The pure yttria phase can form through calcining at 700°C. The Yb3+:Y2O3 nanopowders calcined at 1100°C were well dispersed with a spherical morphology, and had a narrow particle size distribution with a mean particle size of about 70nm. By using 1100°C-calcined powders, nearly full dense Yb3+:Y2O3 ceramics were fabricated at 1750°C for 8h without any additives under vacuum conditions. The fluorescence spectrum of the sintered ceramics illustrates that there are two emission peaks locating at 1028 and 1071nm respectively, all corresponding to the 2 F 5/2 → 2 F 7/2 transitions of Yb3+ ion. Homogeneous Yb3+:Y2O3 nanopowders synthesized by carbonate-precipitation method are suitable for the fabrication of IR-transparent ceramics. [ABSTRACT FROM AUTHOR]

• Solid-state reaction synthesis of Na(Y, Gd)F 4 :Yb3+, Er3+ phosphors. • 980/1550 nm laser excited color-tunable upconversion luminescence. • Gd3+ ion doping can obviously enhance the UC luminescence intensity of the samples. • Applications in bio-science and PV solar cells. A series of Na(Y, Gd)F 4 :Yb3+,Er3+ phosphor samples co-doped with different concentrations of Gd3+, Yb3+ and Er3+ ions were synthesized at 550 °C for 2 h by a solid-state reaction method. The crystal structure and upconversion (UC) luminescence properties of the samples upon 980/1550 nm wavelength excitation were characterized by XRD and emission spectral analysis methods. The XRD analysis showed that the synthesized samples were all pure hexagonal β-NaYF 4 phase. The doping of Gd3+ ions into β-NaYF 4 solid solution matrix can obviously enhance the UC luminescence intensity of the NaYF 4 : Yb3+, Er3+ samples both upon 980 and 1550 nm laser diode excitation. Moreover, the UC emission of the 1550 nm excited Na(Y, Gd)F 4 :Yb3+,Er3+ samples had a better color tunability than that of the UC emission of the 980 nm excited samples. Meanwhile, based on the experimental results, the UC luminescence mechanisms of the sample upon 980 and 1550 nm excitation were also discussed. [ABSTRACT FROM AUTHOR]

Highly transparent Er3+, Yb3+:Y 2 O 3 ceramics were fabricated by pressureless vacuum sintering method using La 2 O 3 and ZrO 2 as compound sintering additives. The microstructure, optical transmittance, upconversion and near-infrared spectral properties of the ceramics were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry and spectroscopic analysis methods. The sintered ceramics displayed a pure cubic Y 2 O 3 phase structure and a nearly pore-free microstructure with homogeneous grain morphology and grain-size distribution. The highest transmittance of Er3+, Yb3+:Y 2 O 3 ceramics sintered at 1800 °C for 14 h with 9 at% of La 2 O 3 and 3 at% of ZrO 2 as compound additives was more than 82% in the range of 380–3000 nm. Under 980 nm wavelength excitation, the ceramics exhibited intense blue, green and red upconversion emission, and broad-bandwidth near-infrared emission centered at 1536 nm, which gives it the potential to act as a high-performance solid-state 1.54 μm near-infrared and upconversion laser gain media. • Pressureless vacuum sintering of highly transparent Er3+, Yb3+:Y 2 O 3 ceramics. • Using La 2 O 3 and ZrO 2 as compound sintering additives. • The highest transmittance of more than 82% was achieved in the range of 380–3000 nm. • The ceramics demonstrated intense blue, green and red upconversion emission. • The ceramics showed broad-bandwidth near-infrared emission centered at 1536 nm. [ABSTRACT FROM AUTHOR]

Abstract: Mg0.20Zn0.80O films have been prepared on quartz substrates by using radio frequency (RF) magnetron sputtering, and metal–semiconductor–metal (MSM) structured photodetectors have been fabricated on the Mg0.20Zn0.80O films employing interdigital Au as metal contacts. We have investigated the effects of electrode spacings on the properties of Mg0.20Zn0.80O MSM photodetectors. It was shown that both of dark currents and responsivities of the devices will decrease with the increasing electrode spacing at the same bias. It was thought that the resistance and the depletion region between the electrodes play important roles in the devices, and the physical mechanism can be explained by a straightforward qualitative model. [ABSTRACT FROM AUTHOR]