Photocatalytic water splitting properties of Cu2+ exchanged Beta zeolites.

Photocatalytic water splitting with solar energy is the most promising and environmentally friendly hydrogen production method. Having an efficient and cost-effective photocatalyst is key to hydrogen production. Cu dopant has been shown to greatly enhance photocatalytic activities. In this work, Cu2+ ions were doped into Beta zeolite powders (Cu-Beta) by the ion exchange method. The hydrogen evolution efficiency of Cu-Beta was much higher than the raw Beta zeolites without Cu loading. After solid phase reaction, the band gap of Cu-Beta reduced from 3.48 eV to less than 2 eV, and as a result enhanced the optical absorption intensity, particularly in the visible region. The best hydrogen evolution efficiency was 102.12 µmol · g-1 · h-1 when the treated temperature was 900 °C (Cu-Beta-900). The temperature of the solid phase reaction had an important influence on the photocatalytic performance of Cu-Beta; a suitable reaction temperature can greatly improve its photocatalytic performance.

Mn4+ activated Al2O3 red-emitting ceramic phosphor with excellent thermal conductivity.

An Al2O3:Mn4+, Mg2+ red emitting ceramic phosphor, which can be effectively excited by ultraviolet and blue light, was successfully synthesized via solid-state reaction in an oxygen and air atmosphere. The ceramic sintered in oxygen atmosphere has higher optical transmittance and stronger luminescence intensity than the ceramic sintered in the air, which is more suitable for LED application. Since the structure of α-Al2O3 is very simple, it is convenient to study the factors affecting the Mn4+ luminescence. The crystal-strength parameter Dq, Racah parameters B and C, and the nephelauxetic ratio ß1 were calculated to investigate the influence of crystal field strength and nephelauxetic effect on the emission of Mn4+ in the Al2O3 host. The ratio of Dq to B was 1.74, which was lower than 2.2. This indicated that the Mn4+ ions in the α-Al2O3 host were in a weak crystal field environment. Under the 395 nm and 460 nm excitations, quantum yields (QY) of the sample were measured to be 46% and 28.7%, respectively. The density measured by the Archimedes method was 3.61 g/cm3. The ceramic also showed an excellent thermal conductivity value, which was as high as 26.27 W·m-1·K-1@30 °C.

Size and distance dependent fluorescence enhancement of nanoporous gold.

Nanoporous gold (NPG) has been reported to provide remarkable fluorescence enhancement of adjacent fluorophores due to the metal-enhanced fluorescence phenomenon (MEF), and the enhancement is related with the characteristic length of nanoporosity. To fully understand the effect of NPG on nearby fluorophores, it is desirable to study systems with well-defined metal-fluorophore distances. In this study we investigated the distance effect by using silica as the spacing layer between fluorophores and NPG. Originating from competition between plasmonic amplifying and metallic quenching, the dye molecule rhodamine 6G was best enhanced by 20-nm SiO2 coated nanoporous gold with the pore size of 36 nm, while the protein phycoerythrin was best enhanced by 15-nm SiO2 coated nanoporous gold with the pore size of 42 nm and the quantum dots were best enhanced by 20-nm SiO2 coated nanoporous gold with the pore size of 42 nm.

Red Emitting Solid-State CDs/PVP with Hydrophobicity for Latent Fingerprint Detection.

Fluorescent carbon dots (CDs) are a new type of photoluminescent nanomaterial. Solid-state CDs usually undergo fluorescence quenching due to direct π-π* interactions and superabundant energy resonance transfer. Therefore, the preparation of solid-state fluorescent CDs is a challenge, especially the preparation of long wavelength solid-state CDs. In this research, long wavelength emission CDs were successfully synthesized by solvothermal methods, and the prepared CDs showed good hydrophobicity. The composite solid-state CDs/PVP (Polyvinyl pyrrolidone) can emit strong red fluorescence, and the quantum yield (QY) of the CDs/PVP powder reaches 18.9%. The prepared CDs/PVP solid-state powder was successfully applied to latent fingerprint detection. The results indicate that the latent fingerprints developed by CDs/PVP powder have a fine definition and high contrast visualization effect, which proves that the prepared CDs/PVP has great application potential in latent fingerprint detection. This study may provide inspiration and ideas for the design of new hydrophobic CDs.

ITO-Induced Nonlinear Optical Response Enhancement of Titanium Nitride Thin Films.

A series of TiN/ITO composite films with various thickness of ITO buffer layer were fabricated in this study. The enhancement of optical properties was realized in the composite thin films. The absorption spectra showed that absorption intensity in the near-infrared region was obviously enhanced with the increase of ITO thickness due to the coupling of surface plasma between TiN and ITO. The epsilon-near-zero wavelength of this composite can be tuned from 935 nm to 1895 nm by varying the thickness of ITO thin films. The nonlinear optical property investigated by Z-scan technique showed that the nonlinear absorption coefficient (ß = 3.03 × 10-4 cm/W) for the composite was about 14.02 times greater than that of single-layer TiN films. The theoretical calculations performed by finite difference time domain were in good agreement with those of the experiments.

Optical Temperature-Sensing Performance of La2Ce2O7:Ho3+ Yb3+ Powders.

In this paper, La2Ce2O7 powders co-activated by Ho3+ and Yb3+ were synthesized by a high temperature solid-state reaction. Both Ho3+ and Yb3+ substitute the La3+ sites in the La2Ce2O7 lattice, where the Ho3+ concentration is 0.5 at.% and the Yb3+ concentration varies in the range of 10~18% at.%. Pumped by a 980 nm laser, the up-conversion (UC) green emission peak at 547 nm and the red emission at 661 nm were detected. When the doping concentration of Ho3+ and Yb3+ are 0.5 at.% and 14% at.%, respectively, the UC emission reaches the strongest intensity. The temperature-sensing performance of La2Ce2O7:Ho3+ with Yb3+ was studied in the temperature range of 303-483 K, where the highest relative sensitivity (Sr) is 0.0129 K-1 at 483 K. The results show that the powder La2Ce2O7:Ho3+, Yb3+ can be a potential candidate for remote temperature sensors.

Structural and Scintillation Properties of Ce3+:Gd3Al3Ga2O12 Translucent Ceramics Prepared by One-Step Sintering.

Cerium-doped gadolinium aluminum gallium garnet (Ce3+:Gd3Al3Ga2O12, Ce3+:GAGG) ceramic is a promising scintillation material. In this study, Ce3+:Gd3Al3Ga2O12 scintillation ceramics were prepared by the one-step sintering of commercially available Gd2O3, Al2O3, Ga2O3, and CeO2 powders in a flowing oxygen atmosphere at 1600 °C by solid-phase reaction sintering. For all the Ce3+:Gd3Al3Ga2O12 ceramic samples doped with different amounts of Ce3+ doping, dense ceramics were obtained. The structure, photoluminescence, and scintillation properties of the Ce3+:Gd3Al3Ga2O12 ceramics have been investigated. The average grain size of samples sintered at 1600 °C is about 2 µm. The X-ray excitation luminescence peak is around 560 nm, which is consistent with that of Ce3+:Gd3Al3Ga2O12 single crystals, matching well with the computed tomography X-ray detector's response sensitivity. The light yield is higher compared to the standard reference sample-lutetium yttrium orthosilicate single crystal.

Tunable Nonlinear Optical Response of ITO Films with Au@Ag Bimetallic Nanoparticles.

The nonlinear optical (NLO) response of indium tin oxide films covered with Au@Ag colloid layer was characterized by a femtosecond single-beam open aperture (OA) Z-scan technique in this study. As the Au@Ag thickness increased, the transition from saturated absorption (SA) to reverse saturated absorption (RSA) was found in these ITO matrix composites. The nonlinear absorption coefficient for these composite materials can be regulated from -6.85 × 10-7 m/W to 26.06 × 10-7 m/W. In addition, this work also characterized the structure, morphology, and other optical properties of the specimen, and the finite-difference time-domain (FDTD) results were consistent with the experimental results. The NLO response of the ITO/Au@Ag composites can be attributed to the phase properties, synergistic competition effect, strong interaction based on the epsilon-near-zero (ENZ) mode, and localized surface plasmon resonance (LSPR) between the indium tin oxide films and Au@Ag.

Color Tunable Composite Phosphor Ceramics Based on SrAlSiN3:Eu2+/Lu3Al5O12:Ce3+ for High-Power and High-Color-Rendering-Index White LEDs/LDs Lighting.

Lu3Al5O12:Ce3+ phosphor ceramics were fabricated by vacuum sintering. On this basis, a bi-layer composite phosphor was prepared by low-temperature sintering to cover the phosphor ceramics with a layer of SrAlSiN3:Eu2+-phosphor-in-glass (PiG). The optical, thermal, and colorimetric properties of LuAG:Ce3+ phosphor ceramics, SrAlSiN3:Eu2+ phosphors and SrAlSiN3:Eu2+-PiG were studied individually. Combining the bi-layer composite phosphors with the blue LED chip, it is found that the spectrum can be adjusted by varying the doping concentration of SrAlSiN3:Eu2+-PiG and the thickness of Lu3Al5O12:Ce3+ phosphor ceramics. The maximal color rendering index value of the white LED is 86, and the R9 is 61. Under the excitation of a laser diode, the maximum phosphor conversion efficacy of the bi-layer composite phosphors is 120 lm/W, the Ra is 83, and the correlated color temperature is 4534 K. These results show that the bi-layer composite phosphor ceramic is a candidate material to achieve high color rendering index for high brightness lighting.

SERS-active WO3-x thin films with tunable surface plasmon resonance induced by defects from thermal treatment.

A series of WO3-x thin films with defects were obtained by thermal treatments from laser irradiation and annealing, respectively. The corresponding tunability of localized surface plasmon resonance properties and the enhancement of Raman scattering intensity were realized due to the defects in the WO3-x thin films after thermal treatments. With the changes of either laser power or annealing temperature, the crystalline quality of WO3-x thin film was declined with a red shift of the surface plasmon resonance wavelength from 464 nm to 482 nm. The as-treated WO3-x film shows good uniformity and reproducibility in Surface-enhanced Raman spectroscopy measurement, the detection limit for dye methylene blue can reach 10-8 mol/L, and enhancement factor is 1.38 × 106. Furthermore, the simulation result of finite-difference time-domain showed a substantial agreement with experimental results.

BaAl2O4:Eu2+-Al2O3 ceramics for wide range optical temperature sensing.

In this paper, BaAl2O4:Eu2+-Al2O3 ceramics were successfully prepared by spark plasma sintering (SPS). The optical properties of the multiphase ceramics doped with different concentrations of alumina were studied. Under excitation with 365 nm ultraviolet light, the luminescent color of the samples can be adjusted by changing the sintering temperature and the contents of alumina addition. The temperature dependent fluorescence spectra in the temperature range of 4 K-434 K were measured, and the temperature dependent fluorescence intensity ratio (FIR) was calculated. The FIR monotonically increased with the increase of temperature, indicating that the material could be used for temperature sensing. The absolute sensitivity Sa of the temperature sensing fluorescent material is larger than 0.005 K-1 at 334 K-434 K, and the relative sensitivity Sr is larger than 0.75% K-1 at 304 K-434 K. The results show that the BaAl2O4:Eu2+-Al2O3 ceramic is a promising non-contact temperature sensing material.