Solid-state Reaction In Vacuum Research Articles

Upconversion luminescence of cubic and hexagonal structured SrTa4O11:Er3+/Yb3+ phosphors.

Cubic and hexagonal structured SrTa4O11(STO):Er3+/Yb3+ phosphors were synthesized by a solid state reaction (SSR) and molten salt synthesis (MSS). The upconversion luminescence (UCL) intensity of these samples was investigated. Hexagonal STO:Er3+/Yb3+ with much or a little β-Ta2O5 can be synthesized by SSR in air or vacuum, respectively, and the UCL intensity of the sample synthesized by SSR in a vacuum is higher. Cubic STO:Er3+/Yb3+ can be synthesized by MSS with KCl flux, and hexagonal STO:Er3+/Yb3+ can be synthesized by MSS with B2O3 flux, which has the strongest UCL intensity among all the samples compared with samples prepared by SSR. The sample by MSS with B2O3 flux was acid pickled (AP) with HCl solution, and the green UCL intensity increased by 2.18 times, which reached 32.95% for β-NaYF4:Er3+/Yb3+. The UCL intensity of the hexagonal STO:Er3+/Yb3+ is much higher than that of the cubic structure, which is due to the layered structure and the non-central symmetry of the Er3+/Yb3+ doped sites in hexagonal STO:Er3+/Yb3+. The temperature sensitivity of samples is evaluated by luminescence intensity ratio (LIR) technology. The maximum relative sensitivity is 0.0099 K-1 at 303 K. All the results show that hexagonal STO:Er3+/Yb3+ has excellent pure green UCL intensity and high temperature sensitivity, which can be used in UCL display and temperature sensing.

Color-tunable and upconversion luminescence of Gd2O2S:Er,Tm phosphor: experimental investigations and first-principles calculation

The Er3+, Tm3+ co-doped gadolinium oxysulfide phosphors were prepared using solid-state reaction in vacuum. The crystal structure, morphology, and photoluminescence characteristics were, respectively, investigated by X-ray diffraction, transmission electron microscope, upconversion luminescence spectra and Commission Internationale de L’Eclairage diagram. Under 980 nm excitation, the quenching concentration of Er3+ was revealed to be 7 mol% with highest luminescence intensity and fluorescence lifetime. The emitting color of Gd2O2S:Er,Tm phosphors can be tuned by adjusting the concentration of Er3+ and Tm3+. First-principles calculation was employed to clarify the luminescence mechanism of the impurities doped in gadolinium oxysulfide host lattice by calculated band structure, density of states and absorption spectrum.

Color-tunable and upconversion luminescence of Gd2O2S:Er,Tb phosphor

Er3+,Tb3+-codoped gadolinium oxysulfide phosphor was prepared using solid state reaction in vacuum. The structure and morphology of the resulting particles were characterized by X-ray diffraction and transmission electron microscope whereas their optical properties were monitored by photoluminescence spectroscopy. The power dependence on color-tunable and upconversion luminescence were also obtained in this paper. Color emission of the synthesized phosphors can be tuned from green to yellow due to Tb3+ ions doping by varying the excitation power from 1.0 W to 2.0 W. The first principles calculation method was employed to study the crystal, electronic structure and optical properties of Gd2O2S:Er crystals, so it was further confirmed that doping of Tb3+ ions played significant role of energy transfer rather than crystal structure of the host lattice.

Microstructure optimization of the composite phase ceramic phosphor for white LEDs with excellent luminous efficacy.

The two-phase MgAl2O4-Ce:YAG ceramic phosphor was fabricated by the solid-state reaction in vacuum, and it presented a better luminous efficacy than the single-phase transparent ceramic phosphor when directly combined with the blue light-emitting diodes. The addition of MgAl2O4 implemented the control of the grain sizes and the variation of microstructure, and the microstructure optimization further improved the luminous efficacy of the composite phase ceramic phosphor. A maximum luminous efficacy attaining 99 lm/W at the correlated color temperature 5000 K was obtained. The composite phase ceramic phosphor is expected to be a promising candidate for use in the high-power light source.

Influence of vacuum upon preparation and luminescence of Si4+ and Ti4+ codoped Gd2O2S:Eu phosphor

As a novel red long afterglow phosphor, Si4+ and Ti4+ ion codoped Gd2O2S:Eu phosphor with spherical morphology, sub-micrometer size and narrow particle size distribution was synthesized by solid-state reaction in vacuum. The vacuum synthesis mechanism was determined by thermal analysis. The crystal structure, luminescence properties and mechanisms were investigated respectively by XRD, SEM and fluorescence spectrophotometer. The results show that well-crystallized Gd2O2S:Eu,Si,Ti phosphors are of hexagonal structure which is in agreement with the standard powder peak positions of Gd2O2S hexagonal phase. It displays pure red emission because of the strongest peaks at 627nm and 617nm which are attributed to energy transfer (5D0–7F2). There is a little blue shift of charge transfer excitation band in the excitation spectra between the bulk and sub-micrometer-sized samples, which may stem from size dependent shift and different lattice distortion in the position of the Eu3+-ligand electron transfer absorption/excitation band. To further study the influence of the impurities in Gd2O2S:Eu crystals on crystal growth, the simulated crystal face and its XRD patterns were illustrated. The preferred orientation of crystal growth changed from crystal face (101) to (100) thus to result in different luminescence mechanisms.

Preparation and photovoltaic properties of N-doped TiO2nanocrystals in vacuum

Abstract

Sintering and Characterization of Zr<sub>2</sub>Al<sub>3</sub>C<sub>5</sub> Monolith

Zr2Al3C5 has been successfully synthesized via solid state reaction between Al, ZrC and carbon powder at 1600 in vacuum. This complex carbide has very strong bond between metal atoms and carbon atoms. Thus, this material has a potential to be utilized as structural materials. Some properties of Zr2Al3C5 powder from solid-state reaction in vacuum had been tested. It was found that this powder was completely oxidized in air at 900 1 h, and can be hydrated in moist air. These drawbacks might come from the high reactivity of the powder due to synthesis in vacuum. Zr2Al3C5 powder from solid state reaction in vacuum was sintered at various temperatures from 1500 to 2000 under vacuum with pulse electric current sintering (PECS) and pressureless sintering. Zr2Al3C5 started to sinter at 1500 and got partially dense from 1700. Physical properties and mechanical properties of this material were investigated and discussed.

Electrooptic Properties of SnSe Thin Films Synthesized by Solid State Reaction

AbstractTin monoselinide thin films were obtained by solid state reaction in vacuum. They were characterised by X‐ray diffraction and subjected to resistivity and optical absorbance measurements. The data were analysed for obtaining activation energy and band gap. The effects of varying deposition parameters were studied. These films are concluded to be superior to those obtained directly from the compound semiconductor.