Yaru Ni

Controllable self-assembly of NaREF4 upconversion nanoparticles and their distinctive fluorescence properties

The paper presents the growth of hexagonal NaYF4:Yb(3+), Tm(3+) nanocrystals with tunable sizes induced by different contents of doped Yb(3+) ions (10%-99.5%) using the thermal decomposition method. These nanoparticles, which have different sizes, are then self-assembled at the interface of cyclohexane and ethylene and transferred onto a normal glass slide. It is found that the size of nanoparticles directs their self-assembly. Due to the appropriate size of 40.5 nm, 15% Yb(3+) ions doped nanoparticles are able to be self-assembled into an ordered inorganic monolayer membrane with a large area of about 10 × 10 μm(2). More importantly, the obvious short-wave (300-500 nm) fluorescence improvement of the ordered 2D self-assembly structure is observed to be relative to disordered nanoparticles, which is because intrinsic absorption and scattering of upconversion nanoparticles leads to the self-loss of fluorescence, especially the short-wave fluorescence inside the disordered structure, and the relative emission of short-wave fluorescence is reduced. The construction of a 2D self-assembly structure can effectively avoid this and improve the radiated short-wave fluorescence, especially UV photons, and is able to direct the design of new types of solid-state optical materials in many fields.

Mutual protection against UV aging of EVA composites using highly active optical conversion additives

The mutual ultraviolet (UV) degradation protection and optical conversion mechanism of ethylene-vinyl acetate copolymer (EVA) rare earth organic complex (REOC) composite were investigated. The uniform Sm(TTA)3Phen (MSTP) particles were successfully synthesized via microwave ultrasonic technique, and were uniformly embedded into the EVA long chain cross-linked structure with excellent dispersion. The MSTP doped EVA film provides an excellent active optical conversion and highly visible transmission performance, the properties of which are strongly dependent on the size and concentration of the doped particle, and its absorption and emission properties. MSTP was effective as a UV light resistant agent and was a highly active optical conversion additive for EVA rare earth organic complex composites with perfect network structure and excellent adhesion properties, which through the destruction of the structure can transform the heat energy into the form of light energy release via hydrogen bonding.

Synthesis and conductivity properties of Gd0.8Ca0.2BaCo2O5+δ double perovskite by sol–gel combustion

Double perovskite oxides Gd0.8Ca0.2BaCo2O5+δ have been successfully prepared by EDTA-citrate complexation process. The prepared samples were characterized by means of thermogravimetry–differential analysis, X-ray diffraction, Fourier transform infrared spectroscopy techniques. These analyses suggested that pure Gd0.8Ca0.2BaCo2O5+δ phase could be formed when the pH value was maintained above three and calcination temperature was higher than 850xa0°C. The conductivity properties analyzed by means of four probes method, scanning electron microscopy and X-ray photoelectron spectroscopy indicated an improvement in conductivity with a high value of nearly 1200xa0S/cm, which was due to an increase in the number of small polaron hopping conduction units, Co3+–O–Co4+. Interestingly, the Gd0.8Ca0.2BaCo2O5+δ samples exhibited a semiconducting behavior through a wide range of temperature below 100xa0°C and a metallic behavior at 100–500xa0°C, thereby demonstrating that Gd0.8Ca0.2BaCo2O5+δ could meet the requirements of a smart material.

High thermal radiation of Ca-doped lanthanum chromite

Calcium-doped lanthanum chromite, La1−xCaxCrO3, was prepared using a solid-state reaction method, and the effect of varying the Ca content (0 ≤ x ≤ 0.5) was investigated in relation to its crystalline structure, surface morphology, solar absorption and thermal radiation. This found that the crystalline structure is slightly distorted by Ca2+ doping, with an accompanying increase in the valence state of Cr ions and oxygen vacancies enhancing both the solar absorption and thermal emittance. Overall, the La1−xCaxCrO3 system displays relatively high thermal radiation properties, with an optimal composition of La0.5Ca0.5CrO3 exhibiting a solar absorption of 95% and a thermal emittance of 0.94. When used as a light absorber coupled to a thermoelectric module this proved capable of generating electricity and hot water, thereby demonstrating the suitability of this energy-saving material for use in solar thermal radiation applications.

Crystal structures and luminescence properties of NaYF4 microcrystals at different pH values

Luminescence properties of materials are closely related to their crystal structures and growth characteristics. In this study, a series of β-NaYF4:20% Yb3+, 2% Er3+ (20 and 2% represent the reactant mole percentage) microcrystals with different morphologies and sizes were synthesized using a hydrothermal route. The crystal phase, morphology, size, and upconversion luminescence properties of the as-prepared samples were characterized by x-ray diffraction, field emission scanning electron microscopy and photoluminescence analysis, respectively. The effects of the precursor solution pH value on the upconversion luminescence properties of the β-NaYF4:Yb3+, Er3+ crystals were investigated in detail. The results indicate that the preferential growth plane of the β-NaYF4 crystals was significantly influenced by the precursor pH values. Crystal plane characteristics affected the luminescence behavior of β-NaYF4 in the red and green spectral range. In addition, reasonable control of the β-NaYF4 crystal growth has a significant effect on the fluorescence lifetime.

Enhancement of fluorescent emission in photonic crystal film and application in photocatalysis

Fluorescent photonic crystal films composed of monodisperse NaYF4:15Yb,0.5Tm@SiO2 (where 15 and 0.5 represent the mole percentage of reactants) core-shell spheres were successfully fabricated and applied in photocatalysis. The core-shell spheres were prepared using a modified Stober method, and fluorescent photonic crystal films were fabricated via a simple self-assembly method. The morphologies, structures and upconversion fluorescent properties of the fluorescent photonic crystal films with different photonic band gaps were characterized. Moreover, their photocatalytic capability in decomposing rhodamine B using near-infrared light was studied. Results indicate that the band edge effect plays a critical role in the enhancement of short wave emission intensity of fluorescent photonic crystal films. Specifically, in comparison to the reference sample without a band edge effect, the 363 nm emission intensity was enhanced by 5.97 times, while the percentage of UV upconversion emission was improved by 6.23%. In addition, the 451 nm emission intensity was enhanced by 5.81 times, and the percentage of visible upconversion emission was improved by 8.88%. Furthermore, fluorescent photonic crystal films with enhanced short wave emission exhibited great photocatalytic performance in the degradation of rhodamine B aqueous solutions under near-infrared light.

Enhancement of fluorescent properties of photonic crystals containing triplet–triplet annihilation upconversion materials via adjusting incident angles

A triplet–triplet annihilation upconversion luminescent (TTA-UCL) material of platinum(II)-octaethylporphyrin and 9,10-diphenylanthracene (PtDPA) was dispersed in the silica photonic crystal (PC) gaps to construct a hybrid fluorescent structure. The morphology, forbidden band effects and fluorescent properties were characterized by field emission scanning electron microscopy, Ultraviolet–Visible spectrophotometer and photoluminescence analysis, respectively. The results indicated that the fluorescent intensity of PtDPA detected from different angles was enhanced with the aid of PC structure and the emission intensity came to the strongest when the emission and excitation peaks of PtDPA were coincident with the forbidden bands of the PC structure. Crystal diffraction theory, finite-difference-time-domain method and plane wave expansion method were used to analyze the effect of incident angle on forbidden band effects of the PC film. The results showed that the forbidden band position of the PC moved from 571 to 400xa0nm when the incident angle changed from 0° to 75° gradually and split into two forbidden bands when the incident angle was larger than 45°. The adjustment of incident angle, thus, provided a convenient way to control the fluorescent properties of TTA-UCL materials coupled with PCs.

Influence of annealing atmosphere on the electrical and spectral properties of Gd0.8Ca0.2BaCo2O5+δ ceramic

For practical applications, the stability of perovskite-like oxides in various environments should be evaluated. In this work, samples of Gd0.8Ca0.2BaCo2O5+δ (GCBC2)were annealed in different atmospheres and at different temperatures, and changes in their spectral reflective properties, infrared radiative properties, and electrical conductivity properties under solar irradiation were investigated using thermogravimetric analyses, reflection spectra measurements, electrical conductivity measurements, and X-ray photoelectron spectroscopy. The results of the study show that oxygen non-stoichiometry is dependent on the temperature and atmosphere used during the annealing process. In an oxygen atmosphere, an increase in oxygen non-stoichiometry was observed up to temperatures of 500xa0°C, and then a decrease at 800xa0°C. In a nitrogen atmosphere, oxygen stoichiometry always decreased at temperature above 400xa0°C. Although an increase in oxygen content had no effect on the ceramic’s electrical and optical properties, a decrease in oxygen content affected its properties significantly. Therefore, because GCBC2 has a typical insulator–metal transition under solar irradiation below 500xa0°C, and a low infrared emissivity in oxidized atmospheres, it can be used as a solar thermal conversion material, or for spacecraft thermal control devices in an oxidized environment.

Novel spectral properties for La0.7Ca0.3CrO3 ceramics by Mo6+ doping

The effects of Mo6+ doping on La0.7Ca0.3CrO3 oxide ceramics synthesized using a solid state reaction method were systematically investigated by thermogravimetric and differential thermal analysis, X-ray diffraction, 3D laser microscopy, UV–Vis spectrophotometry, and infrared diffused reflection measurement. Through these experiments, it was found that the structure, morphology, and spectral properties of the ceramic powders depend on the concentration of Mo6+ ions. Identification and quantification of crystalline phases using Rietveld refinement revealed the presence of Mo-doped calcium lanthanum chromites and calcium molybdate (CaMoO4) in doped oxides with ≤0.5xa0at% Mo, whereas LaCrO3, CaMoO4 and La2Mo2O9 were formed at higher concentrations. The mean surface roughness of all the samples was around 0.2xa0μm, and therefore had little influence on the solar absorptance and infrared emissivity. Calculated values obtained by integrating the spectra identified a low near infrared reflectivity (0.47) with 81xa0% solar absorptance, indicating the possibility of selectively controlling the spectral properties at a specific wavelength to create functional ceramics with variable near infrared reflectivity for use in solar applications.

Novel spectral properties for La 0.7 Ca 0.3 CrO 3 ceramics by Mo 6+ doping

The effects of Mo6+ doping on La0.7Ca0.3CrO3 oxide ceramics synthesized using a solid state reaction method were systematically investigated by thermogravimetric and differential thermal analysis, X-ray diffraction, 3D laser microscopy, UV–Vis spectrophotometry, and infrared diffused reflection measurement. Through these experiments, it was found that the structure, morphology, and spectral properties of the ceramic powders depend on the concentration of Mo6+ ions. Identification and quantification of crystalline phases using Rietveld refinement revealed the presence of Mo-doped calcium lanthanum chromites and calcium molybdate (CaMoO4) in doped oxides with ≤0.5xa0at% Mo, whereas LaCrO3, CaMoO4 and La2Mo2O9 were formed at higher concentrations. The mean surface roughness of all the samples was around 0.2xa0μm, and therefore had little influence on the solar absorptance and infrared emissivity. Calculated values obtained by integrating the spectra identified a low near infrared reflectivity (0.47) with 81xa0% solar absorptance, indicating the possibility of selectively controlling the spectral properties at a specific wavelength to create functional ceramics with variable near infrared reflectivity for use in solar applications.