Heterogeneous CuS QDs/BiVO4@Y2O2S Nanoreactor for Monitorable Photocatalysis.

Exploration of multifunctional integrated catalysts is of great significance for photocatalysis toward practical application. Herein, a 1D confined nanoreactor with a heterogeneous core-shell structure is designed for synergies of efficient catalysis and temperature monitoring by custom encapsulation of Z-scheme heterojunction CuS quantum dots/BiVO4 (CuS QDs/BiVO4) and Y2O2S-Er, Yb. The dispersed active sites created by the QDs with high surface energy improve the mass transfer efficiency, and the efficient electron transport channels at the heterogeneous interface extend the carrier lifetime, which endows the nanoreactor with excellent catalytic performance. Meanwhile, real-time temperature monitoring is realized based on the thermally coupled levels 2H11/2/4S3/2→4I15/2 of Er3+ using fluorescence intensity ratio, which enables the monitorable photocatalysis. Furthermore, the nanoreactor with a multidimensional structure increases effective intermolecular collisions to facilitate the catalytic process by restricting the reaction within distinct enclosed spaces and circumvents potential unknown interaction effects. The design of multi-space nanoconfined reactors opens up a new avenue to modulate catalyst function, providing a unique perspective for photocatalytic applications in the mineralization of organic pollutants, hydrogen production, and nitrogen fixation.

Swallowed Embedding of Nanopetal-Rich Microflowers in Flexible Photocatalytic and Thermoresponsive Functional Composite Fibers.

Developing efficient catalysts to degrade pollutants in water is a very important way to alleviate water pollution. However, it is crucial but challenging to broaden the functions of conventional photocatalysts and improve their environmental adaptability. In this paper, Bi(Er3+/Yb3+)OBr/polyacrylonitrile (BOB-EY/PAN) composite fibers with a swallowed-embedded structure assembled with nanopetal-rich microflowers were designed and fabricated, integrating photocatalytic and temperature-monitoring functions simultaneously. Their unique structure brings a large specific surface area, and the doping of rare earth ions improves the separation efficiency of electron-hole pairs, which enhances the photocatalytic efficiency and endows the fibers with a temperature-monitoring function at the same time. Under simulated sunlight irradiation, the nanofibers show a maximum degradation efficiency of 99.2% for tetracycline hydrochloride (TC) with a degradation constant of K as high as 0.078 min-1. Based on the fluorescence intensity ratio (FIR), the two thermally coupled levels of Er3+ in the nanofibers, 2H11/2 and 4S3/2, provide real-time temperature feedback, displaying a maximum relative sensitivity as high as 0.0215 K-1 at 303 K. Dual-functional BOB-EY/PAN composite nanofibers show great potential for industrial wastewater disposition, providing solutions for wastewater purification in special scenarios.

Heterojunction Photocatalyst Loaded on Electrospun Nanofibers for Synergistic Enhanced Photocatalysis and Real-Time Temperature Monitoring.

Bi2WO6:Ho3+, Yb3+/g-C3N4 (BHY/CN) photocatalysts are successfully loaded on polyacrylonitrile (PAN) nanofibers by electrospinning technology, which combines an upconversion effect and heterojunctions to achieve dual-functional characteristics. Polymer-modified photocatalytic materials offer a large specific surface area of 24.1 m2/g and a pore volume of 0.1 cm3/g, promoting the utility of solar energy. The introduction of rare earth ions and g-C3N4 optimizes the structural band gap, which broadens the light absorption range and promotes electron transfer. Moreover, the heterojunction between Bi2WO6 and g-C3N4 has suppressed the complexation of photoinduced carriers, further improving catalytic performance. The optimized photocatalysts have higher photocatalytic activity with degrading 92.6% tetracycline-hydrochloride (120 min) under simulated sunlight irradiation. The optical thermometry has also been achieved based on the fluorescence intensity ratio technique, where the maximum absolute and relative sensitivity values of BHY/CN-1:6@PAN are 3.322% K-1 and 0.842% K-1, respectively. This dual-functional nanofibers with excellent mechanical properties provide noncontact temperature feedback and efficient catalytic performance for better wastewater treatment and ecological restoration in extreme harsh environments.

Efficient erbium-doped thin-film lithium niobate waveguide amplifiers.

Lithium niobate on insulator (LNOI) is an emerging photonic platform with great promise for use in future optical communications, nonlinear optics, and microwave photonics. An important integrated photonic building block, active waveguide amplifiers, however, are still missing in the LNOI platform. Here, we report an efficient and compact waveguide amplifier based on erbium-doped LNOI waveguides, achieved using a sequence of erbium-doped crystal growth, ion slicing, and lithography-based waveguide fabrication. Using a compact 5 mm long waveguide, we demonstrate an on-chip net gain of >5dB for 1530 nm signal light with a relatively low pump power of 21 mW at 980 nm. The efficient LNOI waveguide amplifiers could become an important fundamental element in future lithium niobate photonic integrated circuits.

All-inorganic perovskite quantum dots-based electrospun polyacrylonitrile fiber for ultra-sensitive trace-recording.

All-inorganic dual-phase CsPbBr3-Cs4PbBr6quantum dots (CPB QDs)-based polyacrylonitrile (PAN) fiber synthesized by supersaturated recrystallization and electrospinning technique possesses characteristics of homogeneous morphology, high crystallinity and solution sensitivity. Under 365 nm laser excitation, CPB@PAN fiber exhibits surprising trace-recording capability attributing to the splash-enhanced fluorescence (FL) performance with a narrow-band emission at 477-515 nm. In the process of ethanol anhydrous (EA) and water splashing, the CPB@PAN fiber presents conspicuous blue and green emission when contacting with EA and water, and maintains intense blue and green FL for more than 4 months. These experimental and theoretical findings provide a facile technology for the development of biological protection display, biotic detection and moisture-proof forewarning based on the trace-recording performance of CPB@PAN fiber.

Fluorescence regulation derived from Eu3+in miscible-order fluoride-phosphate blocky phosphor.

Miscible-order fluoride-phosphate blocky phosphor (FBP), composed with ordered-phase of NaYF4crystals and unordered phase of tin-fluorophosphate glass, is prepared by a two-step process and luminescent properties of FBPs embedded with different particle sizes of NaYF4crystals are presented. High-frequency fluorescence from higher metastable5DJ(J = 1, 2 and 3) energy levels are effectively released in Eu3+doped fluoride crystals. Taking the blue emission of Sn2+as the framework, multi-peak emissions from metastable energy levels are controlled to adjust the color coordinates of the FBP to the white-light region, which the color rendering index (CRI) reaches 89. Tunable color FBP with high CRI retains splendid luminescence property of fluoride, providing a potential candidate for the development of white LED.

Optical damage resistant Ti-diffused Zr/Er-codoped lithium niobate strip waveguide for high-power 980 nm pumping.

Ti4+-diffused Zr4+/Er3+-codoped LiNbO3 strip waveguide was fabricated on an X-cut LiNbO3 substrate by thermal diffusion in sequence of Er3+, Zr4+ and Ti4+. Secondary ion mass spectrometry study shows that the Ti4+ ions follow a sum of two error functions in the width direction and a Gauss function in the depth direction of the waveguide. Both Er3+ and Zr4+ profiles follow the desired Gauss function, and entirely cover the Ti4+ profile. Optical study shows that the waveguide is TE or TM single mode at 1.5 µm wavelength, and has a loss of 0.3 (0.5) dB/cm for the TM (TE) mode. In the case of 980 nm pumping, the waveguide shows stable 1547 nm signal output under high-power pumping without optical damage observed, and a net gain of 1.1 dB/cm is obtained for the available pump power of 120 mW.

Continuous control of the nonlinearity phase for harmonic generations.

The capability of locally engineering the nonlinear optical properties of media is crucial in nonlinear optics. Although poling is the most widely employed technique for achieving locally controlled nonlinearity, it leads only to a binary nonlinear state, which is equivalent to a discrete phase change of π in the nonlinear polarizability. Here, inspired by the concept of spin-rotation coupling, we experimentally demonstrate nonlinear metasurfaces with homogeneous linear optical properties but spatially varying effective nonlinear polarizability with continuously controllable phase. The continuous phase control over the local nonlinearity is demonstrated for second and third harmonic generation by using nonlinear metasurfaces consisting of nanoantennas of C3 and C4 rotational symmetries, respectively. The continuous phase engineering of the effective nonlinear polarizability enables complete control over the propagation of harmonic generation signals. Therefore, this method seamlessly combines the generation and manipulation of harmonic waves, paving the way for highly compact nonlinear nanophotonic devices.

Polarization-insensitive, shallow Ti-diffused near-stoichiometric LiTaO3 strip waveguide for integrated optics.

We report on a Ti-diffused near-stoichiometric (NS) LiTaO3 strip waveguide fabricated by diffusion of an 8 µm wide, 160 nm thick Ti-strip followed by Li-rich vapor transport equilibration. It is found that the waveguide surface caves in ∼60 nm below the crystal surface. X-ray single-crystal diffraction shows that the indentation is due to Ti-induced lattice contraction. Optical studies show that the waveguide is in an NS composition environment, supports TE and TM single-mode propagation at 1.5 µm wavelength, is polarization insensitive, and has a shallow mode field profile and a loss of 0.2/0.3 dB/cm for the TE/TM mode. Secondary ion mass spectrometry analysis shows that the Ti profile follows a sum of two error functions in the width direction and a Gaussian function in the depth direction of the waveguide. With the optimized fabrication condition, the waveguide is promising for developing an optical-damage-resistant device that requires a shallow mode field profile.

Near-stoichiometric Ti-diffused LiNbO(3) strip waveguide doped with Zr(4+).

We report a near-stoichiometric Ti:Zr:LiNbO(3) strip waveguide fabricated from a congruent substrate with a technological process in the following sequence: Zr4+-diffusion-doping, diffusion of 8-µm-wide, 100-nm-thick Ti strips, and post-Li-rich vapor transport equilibration. We show that Zr(4+)-doping has little effect on the LiNbO(3) refractive index, and the waveguide is in a near-stoichiometric environment. The waveguide well supports both the TE and TM modes, shows weak polarization dependence, is in single mode at the 1.5 µm wavelength, and has a loss of ≤0.6/0.8 dB/cm for the TE/TM modes. A secondary ion mass spectrometry analysis shows that the Zr(4+)-profile part with a concentration above the threshold of photorefractive damage entirely covers the waveguide, implying that the waveguide would be optical-damage resistant.

Electro-optically tunable super-broadband filter based on long period grating in Ti:LiNbO3 waveguide.

We report an electro-optically tunable optical filter based on a parallel structure of two long period gratings in the two same Ti:LiNbO3 strip waveguides: one 675-µm-pitch grating in one waveguide and another 880-µm-pitch grating in the other waveguide. The stop-band is observed in the 1.1-1.3 (1.4-1.6) µm spectral region for the grating pitch 675 (880) µm. Its contrast increases linearly to ∼30 dB as the voltage is increased to 300 V, and the linearity is similar for the two cases of 675 and 880 µm pitches. Higher than 300 V, the contrast decreases due to photorefractive (PR) effect and/or over-coupling. Accompanying the contrast modulation, the resonant wavelength is simultaneously linearly tuned by making use of the PR effect. For the 675 (880) µm pitch, the tuning range is 160 (200) nm for the 400 (300) V voltage change range. With the two gratings, one can realize >360 nm super-broadband filtering.

Symmetry-selective third-harmonic generation from plasmonic metacrystals.

Nonlinear processes are often governed by selection rules imposed by the symmetries of the molecular configurations. The most well-known examples include the role of centrosymmetry breaking for the generation of even harmonics, and the selection rule related to the rotational symmetry in harmonic generation for fundamental beams with circular polarizations. While the role of centrosymmetry breaking in second harmonic generation has been extensively studied in plasmonic systems, the investigation of selection rules pertaining to circular polarization states of harmonic generation is limited to crystals, i.e., symmetries at the atomic level. In this Letter we demonstrate the rotational symmetry dependent third harmonic generation from nonlinear plasmonic metacrystals. We show that the selection rule can be imposed by the rotational symmetry of metacrystals embedded into an isotropic organic nonlinear thin film. The results presented here may open new avenues for designing symmetry-dependent nonlinear optical responses with tailored plasmonic nanostructures.

Spin-enabled plasmonic metasurfaces for manipulating orbital angular momentum of light.

Here, we investigate the spin-induced manipulation of orbitals using metasurfaces constructed from geometric phase elements. By carrying the spin effects to the orbital angular momentum, we show experimentally the transverse angular splitting between the two spins in the reciprocal space with metasurface, as a direct observation of the optical spin Hall effect, and an associated global orbital rotation through the effective orientations of the geometric phase elements. Such spin-orbit interaction from a metasurface with a definite topological charge can be geometrically interpreted using the recently developed high order Poincaré sphere picture. These investigations may give rise to an extra degree of freedom in manipulating optical vortex beams and orbitals using "spin-enabled" metasurfaces.

Appropriate solvent NaVO3 for composition analysis of LiNbO3 crystal using chemical method.

It is crucial to find an appropriate solvent for composition analysis of LiNbO(3) crystal by a chemical method, such as inductively coupled plasma atomic emission spectroscopy. We have comparatively studied several solvents for LiNbO(3) crystal, including HF acid, KHSO(4), B(2)O(3), LiBO(2), and NaVO(3). The results show that as the NaVO(3) is used as the solvent, the solubility of LiNbO(3) is as high as 1 g/g at 1000 °C. The dissolving is quite fast. Neither solute nor solvent is lost from the melting during the dissolving procedure. A clear high-concentration solution is obtained. Moreover, it is verified experimentally that such a solution is valid for composition analysis of LiNbO(3) crystal by a chemical method. In contrast, the other solvents suffer from one problem or another. We conclude that NaVO(3) is an appropriate solvent for chemical analysis of LiNbO(3).

Recyclable and flexible Bi(Ho3+-Yb3+)OBr/g-C3N4 composite porous fiber for efficient water purification and real-time temperature sensing.

Herein, an electrospinning porous nanofiber with large specific surface area, excellent flexibility, remarkable tensile strength, and high stability of thermal degradation has been developed by loading Ho3+/Yb3+ co-doped BiOBr/g-C3N4 (BHY/CN) heterojunction photocatalysts on polyacrylonitrile (PAN) nanofibers. The optimized BHY/CN-2 nanofiber demonstrates outstanding photocatalytic activity for the degradation of 98.83% tetracycline (TC, 60 min) and 99.06% rhodamine B (RhB, 90 min) under simulated sunlight irradiation, and maintains a high level of reusability and recycling stability in three cycles. In addition, temperature monitoring of the catalytic degradation process can be feedback by (5F4, 5S2) → 5I8 and 5F5 → 5I8 radiation transitions of Ho3+ with excellent sensitivity. More importantly, the nanofiber luminescence performance is enhanced by the doping of g-C3N4, which maintain the effective upconversion luminescence properties even in water, providing a reliable reference for real-time monitoring and feedback of the operating temperature, and further expanding the application fields of photocatalysts.

Crystal field optimization and fluorescence enhancement of a Mn4+-doped fluoride red phosphor with excellent stability induced by double-site metal ion replacement for warm WLED.

The effective double-site metal ion replacement strategy was adopted to optimize the crystal field environment of a Mn4+-activated fluoride phosphor. In this study, a series of K2yBa1-ySi1-xGexF6:Mn4+ phosphors with optimized fluorescence intensity, excellent water resistance, and outstanding thermal stability was synthesized. The composition adjustment includes two different types of ion substitution based on the BaSiF6:Mn4+ red phosphor: [Ge4+ → Si4+] and [K+ → Ba2+]. X-ray diffraction and theoretical analysis revealed that Ge4+ and K+ could be successfully introduced into BaSiF6:Mn4+ to form new solid solution K2yBa1-ySi1-xGexF6:Mn4+ phosphors. The emission intensity enhancement and slight wavelength shift were detected in different cation replacement procedures. Furthermore, K0.6Ba0.7Si0.5Ge0.5F6:Mn4+ with superior color stability performance possessed a negative thermal quenching phenomenon. Excellent water resistance was also found, which was more reliable than K2SiF6:Mn4+ commercial phosphor. A warm WLED with low correlated color temperature (CCT = 4000 K) and high color rendering index (Ra = 90.6) was successfully packaged by using K0.6Ba0.7Si0.5Ge0.5F6:Mn4+ as the red light component, and it also exhibited high stability for different currents. These findings demonstrate that the effective double-site metal ion replacement strategy can open up a new avenue for designing new Mn4+-doped fluoride phosphors to improve the optical properties of WLEDs.

Superbroadband near-infrared emission and energy transfer in Pr3+-Er3+ codoped fluorotellurite glasses.

We report the first demonstration of superbroadband emission extending from 1.30 to 1.68 µm in praseodymium(Pr(3+))-erbium(Er(3+)) codoped fluorotellurite glasses under 488 nm excitation. This superbroad near-infrared emission is contributed by the Pr(3+): (1)D(2)→(1)G(4) and Er(3+): (4)I(13/2)→(4)I(15/2) transitions which lead to emissions located at 1.48 and 1.53 µm, respectively. The quenching of the Pr(3+) emission resulted from the cross relaxation [(1)D(2), (3)H(4)]→[(1)G(4), (3)F(3,4)] was effectively compensated by the codoping of Er(3+). The results suggest that, other than the heavy-metal and transition-metal elements of active bismuth (Bi), nickel (Ni), chromium (Cr), etc., Pr(3+)-Er(3+) codoped system is a promising alternative for the broadband near-infrared emission covering the expanded low-loss window.

Superbroadband near-IR photoluminescence from Pr3+-doped fluorotellurite glasses.

Praseodymium(Pr3+)-doped fluorotellurite glasses were synthesized and broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 µm was observed under both 488 and 590 nm wavelength excitations. The broadband PL emission is mainly due to the radiative transition from the manifolds Pr3+: 1D2 to 1G4. The PL line-shape, band width, and lifetime were modified by the Pr3+ dopant concentration, and a quantum efficiency as high as 73.7% was achieved with Pr3+ dopant in a low concentration of 0.05 mol%. The good spectroscopic properties were also predicted by the Judd-Ofelt analysis, which indicates a stronger asymmetry and covalent bonding between the Pr3+ sites and the matrix lifgand field. The large stimulated emission cross-section, long measured lifetime, and broad emission bandwidth confirm the potential of the Pr3+-singly doped fluorotellurite glass as broadband luminescence sources for the broadband near-infrared optical amplifications and tunable lasers.

Influence of postgrowth Li-poor vapor-transport equilibration on the surface Li2O content of a congruent LiNbO3 crystal.

The influence of Li-poor vapor-transport equilibration (VTE) on the surface Li(2)O content of initially congruent X- and Z-cut LiNbO(3) crystal plates was studied against the VTE temperature and time. The VTE-induced surface-Li(2)O-content reduction was evaluated from the measured birefringence. The results show that the reduction and VTE temperature follow the traditional Arrhenius law with a surface-Li(2)O-content alteration constant of (1.0 ± 0.2) × 10(8)/(1.6 ± 0.2) × 10(10) mol % and an activation energy (2.2 ± 0.2)/(2.8 ± 0.2) eV for the X/Z-cut plate, and the reduction has a square-root dependence on the VTE time, ΔC(X) = 0.15t(0.5) for the X-cut plate and ΔC(Z) = 0.167t(0.5) for the Z-cut plate. A generalized empirical expression that relates the reduction to both the VTE temperature and duration is presented. The expression is useful for producing an off-congruent, Li-deficient LiNbO(3) plate with the desired surface Li(2)O content via adjustment of the VTE temperature and duration. On the basis of the known VTE time dependence on the surface-Li(2)O-content reduction, a solution to the Li(+) out-diffusion equation, an integral of the error function complement, is obtained and verified by previously reported experimental results. The results also show that the VTE displays slight anisotropy and is slightly faster along the optical axis direction of the crystal. The Li-poor VTE is a slow process. At 1100 °C, the Li-poor VTE time required for the surface Li(2)O content reaching the Li-deficient boundary is about 400/323 h for the X/Z-cut plate.

Sharp plasmonic resonance on gold gratings in amplitude and phase domains.

In this work, we experimentally studied sharp plasmonic resonance on gold gratings in both amplitude and phase domains using a spectroscopic ellipsometry technique. We used numerical and analytical models to analyze the phase delay of TM and TE waves under a surface plasmon excitation condition, and the calculated result fits well with the experimental observations. In addition, the ellipsometry method used here provides an important tool to characterize the phase information in plasmonic and metamaterial devices.