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Enhanced green and red upconversion emissions under 980 nm excitation are observed in Ba0.85−xCa0.15TiO3:0.75%Er3+/xIn3+ lead-free ferroelectric ceramics which were synthesized by solid state reaction method. With increasing In3+ ions doping level from x = 0% mol the green and red emission intensities increase and reach the maximum at x = 1.75% mol. The maximum intensity of green emission at 550 nm is 20 times larger than In3+ ions undoped samples, which is unprecedented for Er3+-doped perovskite ferroelectric materials. Based on the ultraviolet-visible-near infrared absorption spectra, the enhancement of the luminescence intensity of the A-site In3+ doped Ba0.85−xCa0.15TiO3:0.75%Er/xIn ceramics is attributed to In3+-doping-induced relative increase in isolate Er3+ and decrease in the clustered-Er3+. The effects of In3+ doping on the crystal structure, dielectric, ferroelectric, piezoelectric properties of the ceramics were also studied and discussed.

A series of erbium- and indium-doped 0.965K0.40Na0.58Li0.02Nb0.96Sb0.04O3–0.035Bi0.5K0.5ZrO3:0.25%Er/xIn lead-free piezoelectric ceramics with upconversion photoluminescence (UCPL) properties were prepared by the conventional solid state reaction. A systematical investigation into the effects of In3+ doping on the structural, dielectric, ferroelectric, piezoelectric, and UCPL properties of the ceramics was carried out. The distribution of Er3+-sites could be modified by In3+ doping according to the analysis of UV–Vis-NIR absorption cross-section, resulting in improved piezoelectric and photoluminescence properties of the ceramics. The optimized comprehensive properties are performed by the x = 0.25% samples of which the piezoelectric coefficient d33 ~ 257 pC/N, Curie temperature TC ~ 273 °C, remanent polarization Pr ~ 12.5 µC/cm2, dielectric constant er ~ 1551, and d33 ~ 257 pC/N which is the supreme piezoelectric coefficient achieved in KNN-based UCPL ceramics as of now. The results demonstrate that erbium and indium co-doped KNN-based ceramics may have potential applications in electro-optical devices.

A back-illuminated metal–insulator–semiconductor (MIS) structure AlGaN-based solar-blind ultraviolet photodiode is demonstrated for the purpose of overcoming the technical bottleneck caused by high Al content p-AlGaN in p–i–n structure. The device presents a peak responsivity of 0.115 A/W at 270 nm, corresponding to an external quantum efficiency (EQE) of 53% and an ultraviolet/visible rejection ratio of more than three orders of magnitude under zero-bias. Moreover, a response speed around 24 µs and a peak responsivity of 0.154 A/W, corresponding to an EQE of 70.6% will be achieved at a reverse bias of 3 V. The excellent performances of the back-illuminated MIS photodetector can be attributed to the adoption of a thin n-AlGaN layer of Al content gradient which plays a role of completely relaxing the strain of light absorption layer and the introduction of a homogeneous n-AlGaN interlayer into light absorption region which redistributes its electric field in favor of the separation and transport of the photo-generated carriers.

Strongly correlated perovskite transition-metal oxides have received considerable attention due to their intriguing physical properties, including a metal-insulator transition that can be used in devices. Key questions remain, though, including whether in-plane tensile strain helps or hinders the transition. This study uses both static and dynamic lattice strain to manipulate the transport properties of NdNiO${}_{3}$ films systematically. The electric-field-tunable ferroelastic/piezoelectric strain approach can be used not only to obtain deeper insight into the intrinsic properties of nickelate films, but also as a simple, energy-efficient means to construct multistate resistive memory.

Tea catechins as a member of flavan-3-ols subclass with the same skeleton may behave differentially. This study investigated the chemical conversions of 8 catechins under heat treatment with the involvement of epimerization, hydrolysis and oxidation/condensation reactions. Three reactions were enhanced as temperature increased from 30 °C to 90 °C. The epimerization of non-gallated catechins was favored by epi-configuration but hindered by pyrogallol moiety, and the hydrolysis reaction of gallated catechins was facilitated by pyrogallol moiety. Epicatechin and epigallocatechin had the lowest thermostabilities due to epimerization and oxidation/condensation reactions respectively. Sufficient O2 was not a precondition for the occurrence of chemical conversions of catechins under heat treatment. Non-enzymatic oligomerization occurred to epi type catechins and catechin under heat treatment, and dehydrodicatechins A were mainly responsible for the browning of epicatechin and catechin solutions. The evidence of generation of catechin oligomers provides a novel way to explain sensory change of tea and relevant products during thermal processing.

Summary Desorption of catechins and caffeine from polyvinylpolypyrrolidone (PVPP) was comprehensively investigated. The result showed that caffeine could easily be desorbed from PVPP by the tested solvents except n-hexane, while catechins could only be thoroughly done by dimethyl sulphoxide (DMSO) and N, N-dimethylformamide (DMF). Excellent desorption efficiency of DMSO and DMF might be attributed to their high dipole moments and H-bond potentials. Addition of ethanol was recommended considering the elution efficiency and fluidity, but ethanol volume should be

Interactions of black tea polyphenols (BTP) and green tea polyphenols (GTP) with whole milk were comparatively studied. Upon the ultracentrifugation of BTP– and GTP–milk systems (40% v/v milk), most BTP and GTP partitioned into milk protein fractions: whey proteins and casein micelles, with 35.1% and 73.0% of total catechins bound to the casein micelles accordingly. The affinities of catechins for casein micelles were differentiated by the structures of catechins in the GTP–milk system but the BTP–milk system, being enhanced by a gallate group in catechins and the cis-form and weakened by a pyrogallol group. Fourier transforms infrared spectroscopy (FTIR) analysis showed that TP binding altered the secondary structures of milk proteins by reducing inter β-sheet, random coil and the large loop and increasing α-helix, intra β-sheet and turn structures, and more intense hydrophobic interaction was observed in the BTP–milk system. UV–vis spectra indicated no obvious impacts on TP molecules at a low concentration of milk proteins. With the increasing addition of tea infusion, BTP exhibited a similar fluorescence quenching ability to GTP, but the variance in the ORAC values of BTP–milk system was different from that of the GTP–milk system, suggesting that fluorescence quenching may not fully represent the interactions between polyphenols and proteins.

Adsorbent is one of the most important factors for separation efficiency in fixed-bed purification techniques. The adsorption behavior of catechins and caffeine onto polyvinylpolypyrrolidone (PVPP) was investigated by static adsorption tests. The results showed that catechins rather than caffeine were preferred to adsorb onto PVPP since the adsorption selectivity coefficient of total catechins vs caffeine was around 22.5, and that adsorption of catechins could be described by the pseudo-second-order model. Adsorption amount of caffeine onto PVPP in green tea extracts solution was much higher than that in purified caffeine solution although the initial concentration of caffeine was similar in the two solutions, indicating the caffeine might be attached with catechins which were adsorbed by PVPP instead of being adsorbed by PVPP directly. The results also showed that the adsorption capacity of catechins and caffeine decreased with an increase in temperature, and that Freundlich and Langmuir models were both suitable for describing the isothermal adsorption of catechins, but not suitable for caffeine. The predicted maximum monolayer adsorption capacity of total catechins by PVPP was 671.77 mg g(-1) at 20 °C, which was significantly higher than that by other reported adsorbents. The thermodynamics analyses indicated that the adsorption of catechins onto PVPP was a spontaneous and exothermic physisorption process, revealing lower temperature was favorable for the adsorption of catechins. Elution tests showed that the desorption rates of catechins and caffeine were higher than 91% and 99% after two elution stages; in detail, almost all of the caffeine could be washed down at the water eluting stage, while catechins could be recovered at the dimethyl sulfoxide/ethanol solution eluting stage. Thus, the PVPP could be used as an excellent alternative adsorbent candidate for separating catechins from crude tea extracts, although some investigations, such as exploring the new eluants with low boiling point and high desorption efficiency, should be conducted furthermore.

We epitaxially grew 7 mol. % Nd-doped BaSnO3 (NBSO) thin films on double-side polished SrTiO3 (001) single-crystal substrates and optimized the oxygen pressure (PO2), substrate temperature (TS), and film thickness (t) to achieve excellent structural, optical, and electrical performance. By keeping TS (=800 °C) constant, NBSO films prepared at PO2 = 10 Pa show the best crystallization, yielding a full-width at half-maximum (FWHM) of the x-ray diffraction rocking curve of 0.079° and exhibiting a room-temperature resistivity (ρ) of ∼1.85 mΩ cm and a volume carrier density (n) of ∼8.5 × 1020/cm3. By keeping PO2 (=10 Pa) constant, the room-temperature ρ of NBSO films could be reduced to as low as 0.5 mΩ cm by increasing TS from 700 to 825°; meanwhile, the volume carrier density and mobility show the maximum of 5.04 × 1020/cm3 and 24.9 cm2/Vs, respectively, for TS = 825 °C. For all as-grown NBSO thin films, the optical transmittance in the visible wavelength region is larger than 80%. The optimized comprehensive properties of the NBSO films with FWHM = 0.11°, ρ = 0.5 mΩ cm, μ = 24.9 cm2/Vs, and T > 80% are superior to those of other rare-earth and 4d- and 5d-transition metal-doped BaSnO3 thin films.