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Abstract: Broadband 1.20μm emission originating from the Thulium (Tm3+): 1G4 → 3H4 transition was observed in Tm3+-doped gallogermanate glasses under 476.5nm excitation. The stimulated emission cross-section is calculated to be 2.85×10–21 cm2 using the Füchtbauer–Ladenburg approach. Difficulty in the population inversion between the upper 1G4 and lower 3H4 levels resulting from the cross relaxation process Tm3+ [1G4, 3H6]→[3H4, 3H5] was overcome by the incorporation of Terbium (Tb3+) and Europium (Eu3+) ions. A Judd–Ofelt analysis was performed based on the absorption spectrum and the derived intensity parameters (Ω 2 =4.65×10–20, Ω 4 =1.51×10–20, and Ω 6 =1.42×10–20 cm2) reveal a strong asymmetry and covalent environment between Tm3+ ions and ligands in the host matrix. The results indicate that the Tm3+/Tb3+, Eu3+ codoping scheme is promising in the development of amplifiers and lasers operating at the relatively unexplored 1.2μm wavelength region. [Copyright &y& Elsevier]

Abstract: Diffusivity of Li+ in 5mol% (in growth melt) MgO-doped LiNbO3 crystal has been studied as a function of Li2O-content ranging from 43.4 to 44.4mol% under different temperatures. First, diffusion-limited Li2O-content depth profiles were produced by carrying out Li-poor vapour transport equilibration (VTE) treatments on two 0.5-mm-thick MgO-doped LiNbO3 plates at 1100 and 1130°C for 40h. Second, the profiles were obtained by alternatively doing the optical polish to one crystal surface and the Li2O-content characterization on the polished surface through the measurement of birefringence. Third, Boltzmann–Matano method was applied to the profile to derive the Li+ diffusivity as a function of Li2O-content. The results show that the diffusivity decreases with the reduced Li2O-content by at least two orders of magnitude as the Li2O-content reduces by 1mol% from the as-grown state. In the Li2O-content range studied, the diffusivity at 1130°C is at least two times larger than that at 1100°C. In addition, we also studied the time dependence of the Li-poor-VTE-induced reduction of Li2O-content on surface of the same MgO-doped crystal. The results show that the surface Li2O-content reduction induced has a square-root dependence on the VTE duration. Based upon this dependence, the mathematical solution to the Li+ diffusion equation, an integral of error function complement, is obtained and verified by the experimental result. It is concluded that the MgO doping has less effect on both the Li+ diffusivity and the dependence of surface Li2O-content reduction on the VTE duration. [Copyright &y& Elsevier]

Abstract: We have measured OH absorption spectra of a 0.47-mm-thick Z-cut MgO (5mol% in melt):LiNbO3 crystal subjected to post-growth Li-poor vapor transport equilibration (VTE) treatments at 1100°C for different durations ranging from zero to 395h. These spectra allow the evolution of OH absorption characteristics with prolonged VTE to be followed. After 2h of VTE process an additional absorption appears at 3483cm−1. A transition regime that the original 3536cm−1 and new 3483cm−1 absorptions simultaneously appear exists within the VTE duration range of 2–16h. In this regime, the 3536cm−1 absorption becomes weak gradually and eventually disappears around 16h while the 3483cm−1 absorption increases remarkably with the prolonged VTE. The presence of transition regime gives a hint that the 3483cm−1 absorption is due to the VTE-induced formation of a new center. Based upon the spectral features, we have suggested a simple three-layer (two on surface and one in the center of crystal plate) model to describe the depth profile of the photorefractive damage MgO concentration threshold in the crystal in the transition regime. A Li out-diffusion theory is suggested and correlated with the model. To support the Li out-diffusion theory, some additional experiments have been done. These include the depth profile characterization of VTE-induced Li2O content reduction and the measurement of the surface Li2O content as a function of the VTE duration. A quantitative analysis and discussion shows that the model is well supported by the experimental results. [Copyright &y& Elsevier]

Abstract: Efficient infrared emissions at 1.20μm [5I6 → 5I8 transition] and 1.38μm [(5 F4, 5 S2)→ 5I5 transition] from Ho3+-doped lithium–barium–bismuth–lead (LBBP) glass were observed. The stimulated emission cross-sections were calculated to be 0.29×10−20 and 0.25×10−20 cm2 for 1.20 and 1.38μm emissions, respectively. Judd-Ofelt characteristic parameters Ω2, Ω4 and Ω6 for Ho3+ in LBBP glass were calculated to be 6.72×10−20, 2.35×10−20 and 0.61×10−20 cm2, respectively, which indicates a strong asymmetry and a covalent environment between the Ho3+ ions and the ligands in this glass. The optical amplifications operating at these relatively unexplored wavelength regions were evaluated and discussed. [Copyright &y& Elsevier]

Miscible-order NaGdF 4 fluoride-phosphate phosphor has been synthesized based on tin-fluorophosphate glass with low-melting-point, retaining excellent luminescence property of fluoride nanoparticles. Multi-peak emissions from metastable 5D J (J = 0, 1, 2 and 3) levels are released effectively in the Eu3+ doped fluoride nanoparticles, which lifetimes are at the order of millisecond and quantum efficiency at 5D 0 level in high Eu3+ concentration still remains 88.9%. On the basis of multi-peak emissions from Eu3+ and wide-band blue framework from Sn2+, the color coordinates of the fluoride-phosphate phosphors are regulated to the white light region and the color rendering index reaches up to 88. Tunable color and high color rendering index make fluoride-phosphate phosphor become a potential candidate for high-quality white light source. • Miscible-order fluoride-phosphate phosphor possesses tunable white lighting. • Relative-discrete fluoride-phase retains ability to produce multi-peak emissions. • Quantum efficiency at 5D 0 level in high Eu3+ concentration still remains 88.9%. • Color coordinates are driven to white region and color rendering index reaches 88. • Tunable-color fluoride-phosphate phosphor exhibits attractive potential in WLED. [ABSTRACT FROM AUTHOR]

Electrospun nanofibers of Eu(BA) 3 Phen doped polyacrylonitrile (PAN) have been prepared and the surface radiation-regulation effect of flexible fibers is revealed. Fluorescence contrast between bulks and nanofibers confirmed that the fibrosis process facilitated spectral reshaping and enhanced energy transfer efficiency of ligands to rare earth ions. Due to the enhanced surface radiation-regulation effect, the quantum efficiency of Eu(BA) 3 Phen/PAN nanofibers remains on an upward tendency as Eu(BA) 3 Phen content increasing, and the maximum quantum efficiency of fibers reaches to 86.7%. Large emission cross-section and high radiation transition probability for 5D 0 → 7F 2 of Eu3+ reach up to 4.043 × 10−21 cm2 and 518.79 s−1, respectively, which indicates that the europium-complexes/PAN nanofibers possess great emissive ability. Accordingly, the nano-sized rare-earth fluorescence materials with high quantum efficiency and excellent flexibility obtained by electrospun fibrosis compensate the brittle defects of bulks, which provides a breakthrough in developing light-converting materials. Nanoscale Eu(BA) 3 Phen/PAN flexible fibers with great emissive ability and high quantum efficiency provide a breakthrough in developing light-converting materials. [Display omitted] • Nanoscale Eu(BA) 3 Phen/PAN polymer fibers with smooth surface were prepared. • Spectral reshaping and flexibility enhancement were achieved during fibrosis. • The σ em and A ij for 5D 0. → 7F 2 of Eu3+ reach up to 4.043 × 10−21 cm2 and 518.79 s−1. • Anomalous concentration dependency occurs due to surface radiation-regulation effect. • Bonding of great emissive ability and high QE extend light-converting film region. [ABSTRACT FROM AUTHOR]

• SSON:Eu and CASN:Eu phosphors were introduced in Sn-F-P-O glass by one-step-sintering. • F-migration behavior from glass matrix to phosphors was first investigated in detail. • A mechanism of enhanced PL intensity for Sn2+ caused by doped phosphors was proposed. • PiG with full-visible-spectrum emission shows qualities of CRI (91) and CCT (4993 K). • PiG pumped by NUV LED chip will be a promising candidate for solid warm light source. ga1 Herein, the phosphor-in-glass (PiG) with full-visible-spectrum emission has been successfully fabricated by incorporating SrSi 2 O 2 N 2 : Eu2+ (SSON:Eu) and CaAlSiN 3 : Eu2+ (CASN:Eu) phosphors in ultra-low melting Sn-F-P-O glass using one-step sintering method. The Sn2+ ions show intense blue-green emission characteristics under the excitation of NUV chips, which are highly dependent on its coordination environment in Sn-F-P-O glass. Then, it was investigated in detail for the first time that fluoride from Sn-F-P-O glass substrate migrates and gathers around the embedded phosphors, which is closely related to the emission performance of Sn2+ activators in the PiG. Furthermore, the mechanism of enhancing the PL intensity of Sn2+ ions by embedded phosphors is proposed. As a result, the PiG with full-visible-spectrum emission can be achieved under 370 nm excitation. Importantly, the PiG pumped by NUV LED chips shows excellent-quality white-light with high CRI (Ra = 91) and lower CCT (4993 K). The WLED based on this PiG has been demonstrated as a promising candidate for solid warm light source in the future because of the excellent optoelectronic performance and easy-preparation process. [ABSTRACT FROM AUTHOR]

Na(Y 1−x−y Er x Yb y)F 4 /PAN (NYF-EY/PAN) composite fibers have been successfully fabricated by electrospinning method, and sub-micron embedded crystals in the fibers have presented complete hexagonal structure and thermal reaction function. Effective green up-conversion (UC) fluorescence that originated from flexible fibers can be adapted to microdomain non-contact temperature measurement, complying temperature acquisition for complex geometry and active biological tissue without destroying the temperature field. The maximum absolute sensitivity and the maximum relative sensitivity are 0.00446 K−1 at 423 K and 1.148% K−1 at 303 K, respectively. Composite fibers in which crystallites embedded have superior performances of greater stability and higher sensitivity, are served as micron scale special temperature sensor. Morphology of electrospun fibers embedded with microcrystal, and relationship between sensitivity and temperature based on green up conversion emission. Image 1 • PAN fibers embedded with submicron NaYF 4 microcrystal have been prepared. • Hydrothermal synthesis and electrospun methods are adopted to fiber fabrication. • Effective green up-conversion emissions of Er3+ are served for temperature sense. • Maximum relative sensitivity reaches to 1.148% K−1 at 303 K in composite fibers. • Bonding of sensitivity and flexibility extends sense-suitable region. [ABSTRACT FROM AUTHOR]

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/BiVO 4 (CuS QDs/BiVO 4 ) and Y 2 O 2 S-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 2 H 11/2 / 4 S 3/2 → 4 I 15/2 of Er 3+ 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., (© 2024 Wiley‐VCH GmbH.)

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(Er 3+ /Yb 3+ )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 Er 3+ in the nanofibers, 2 H 11/2 and 4 S 3/2 , 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.

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 Ho 3+ /Yb 3+ co-doped BiOBr/g-C 3 N 4 (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 ( 5 F 4 , 5 S 2 ) →  5 I 8 and 5 F 5  →  5 I 8 radiation transitions of Ho 3+ with excellent sensitivity. More importantly, the nanofiber luminescence performance is enhanced by the doping of g-C 3 N 4 , 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., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Bi 2 WO 6 :Ho 3+ , Yb 3+ /g-C 3 N 4 (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 m 2 /g and a pore volume of 0.1 cm 3 /g, promoting the utility of solar energy. The introduction of rare earth ions and g-C 3 N 4 optimizes the structural band gap, which broadens the light absorption range and promotes electron transfer. Moreover, the heterojunction between Bi 2 WO 6 and g-C 3 N 4 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.

The effective double-site metal ion replacement strategy was adopted to optimize the crystal field environment of a Mn 4+ -activated fluoride phosphor. In this study, a series of K 2 y Ba 1- y Si 1- x Ge x F 6 :Mn 4+ 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 BaSiF 6 :Mn 4+ red phosphor: [Ge 4+ → Si 4+ ] and [K + → Ba 2+ ]. X-ray diffraction and theoretical analysis revealed that Ge 4+ and K + could be successfully introduced into BaSiF 6 :Mn 4+ to form new solid solution K 2 y Ba 1- y Si 1- x Ge x F 6 :Mn 4+ phosphors. The emission intensity enhancement and slight wavelength shift were detected in different cation replacement procedures. Furthermore, K 0.6 Ba 0.7 Si 0.5 Ge 0.5 F 6 :Mn 4+ with superior color stability performance possessed a negative thermal quenching phenomenon. Excellent water resistance was also found, which was more reliable than K 2 SiF 6 :Mn 4+ commercial phosphor. A warm WLED with low correlated color temperature (CCT = 4000 K) and high color rendering index ( R a = 90.6) was successfully packaged by using K 0.6 Ba 0.7 Si 0.5 Ge 0.5 F 6 :Mn 4+ 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 Mn 4+ -doped fluoride phosphors to improve the optical properties of WLEDs.

All-inorganic dual-phase CsPbBr 3 -Cs 4 PbBr 6 quantum 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., (© 2021 IOP Publishing Ltd.)

Miscible-order fluoride-phosphate blocky phosphor (FBP), composed with ordered-phase of NaYF 4 crystals 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 NaYF 4 crystals are presented. High-frequency fluorescence from higher metastable 5 D J ( J  = 1, 2 and 3) energy levels are effectively released in Eu 3+ doped fluoride crystals. Taking the blue emission of Sn 2+ 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., (© 2021 IOP Publishing Ltd.)

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 >5 d B 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.

Na(Y 1- x - y Ho x Yb y )F 4 /PAN (NYF-HY/PAN) composite fibers were synthesized using an electrospinning method, and the sub-micron crystals embedded in the fibers had complete hexagonal crystal structures. Under 977 nm laser excitation, strong green and red up-conversion (UC) emission that originated from flexible fibers were due to the radiative transitions ( 5 F 4 , 5 S 2 ) → 5 I 8 and 5 F 5 → 5 I 8 of Ho 3+ , respectively. The effective green fluorescence emission (539 and 548 nm) can be applied to micro-domain non-contact temperature measurements, realizing rapid and dynamic temperature acquisition in a complex environment without destroying the temperature field. In the temperature range of 313-393 K, the absolute and relative sensitivity of the fibers are 0.00373 K -1 and 0.723% K -1 , respectively, which indicates that the NYF-HY/PAN composite fibers have good thermal sensitivity. Composite fibers in which crystallites are embedded have superior properties, with great stability, high sensitivity, and excellent flexibility, providing a reliable reference for developing temperature-sensing materials for the biomedical field., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In recent years, surface-enhanced Raman scattering (SERS) of a molecule/metal-semiconductor hybrid system has attracted considerable interest and regarded as the synergetic contribution of the electromagnetic and chemical enhancements from the incorporation of noble metal into semiconductor nanomaterials. However, the underlying mechanism is still to be revealed in detail. Herein, we report an irreversible accumulated SERS behavior induced by near-infrared (NIR) light irradiating on a 4-mercaptobenzoic acid linked with silver and silver-doped titanium dioxide (4MBA/Ag/Ag-doped TiO 2 ) hybrid system. With increasing irradiation time, the SERS intensity of 4MBA shows an irreversible exponential increase, and the Raman signal of the Ag/Ag-doped TiO 2 substrate displays an exponential decrease. A microscopic understanding of the time-dependent SERS behavior is derived based on the microanalysis of the Ag/Ag-doped TiO 2 nanostructure and the molecular dynamics, which is attributed to three factors: (1) higher crystallinity of Ag/Ag-doped TiO 2 substrate; (2) photo-induced charge transfer; (3) charge-induced molecular reorientation.

Multivariate terbium-complexes were incorporated into polyacrylonitrile (PAN) and electrospun into flexible multifunctional nanofibers with a uniform diameter of ~200 nm. Fluorescence comparison in multi-ligand-binding nanofibers under ultraviolet (UV) radiation verifies that the differentiated β-diketone ligands with dual functions are the primary cause of the spectral fluctuation, adequately illustrating the available methods for the quantification of intermolecular reciprocities between organic ligands and central Tb 3+ ions. Especially under 308 nm UVB-LED pumping, the total emission spectral power of supramolecular Tb-complexes/PAN nanofibers are identified to be 2.88 µW and the total emission photon number reaches to 7.94 × 10 12  cps which are nearly six times higher than those of the binary complex ones in the visible region, respectively. By modifying the sorts of organic ligands, the luminous flux and luminous efficacy of multi-ligand Tb-complexes/PAN nanofibers are up to 1553.42 μlm and 13.72 mlm/W, respectively. Efficient photon-releasing and intense green-emission demonstrate that the polymer-capped multi-component terbium-complexes fibers have potential prospects for making designable flexible optoelectronic devices.

Using CMOS-compatible Pd catalysts, we demonstrated the formation of high-mobility ⟨111⟩-oriented GaSb nanowires (NWs) via vapor-solid-solid (VSS) growth by surfactant-assisted chemical vapor deposition through a complementary experimental and theoretical approach. In contrast to NWs formed by the conventional vapor-liquid-solid (VLS) mechanism, cylindrical-shaped Pd 5 Ga 4 catalytic seeds were present in our Pd-catalyzed VSS-NWs. As solid catalysts, stoichiometric Pd 5 Ga 4 was found to have the lowest crystal surface energy and thus giving rise to a minimal surface diffusion as well as an optimal in-plane interface orientation at the seed/NW interface for efficient epitaxial NW nucleation. These VSS characteristics led to the growth of slender NWs with diameters down to 26.9 ± 3.5 nm. Over 95% high crystalline quality NWs were grown in ⟨111⟩ orientation for a wide diameter range of between 10 and 70 nm. Back-gated field-effect transistors (FETs) fabricated using the Pd-catalyzed GaSb NWs exhibit a superior peak hole mobility of ∼330 cm 2 V -1 s -1 , close to the mobility limit for a NW channel diameter of ∼30 nm with a free carrier concentration of ∼10 18 cm -3 . This suggests that the NWs have excellent homogeneity in phase purity, growth orientation, surface morphology and electrical characteristics. Contact printing process was also used to fabricate large-scale assembly of Pd-catalyzed GaSb NW parallel arrays, confirming the potential constructions and applications of these high-performance electronic devices.

Ti 4+ -diffused Zr 4+ /Er 3+ -codoped LiNbO 3 strip waveguide was fabricated on an X-cut LiNbO 3 substrate by thermal diffusion in sequence of Er 3+ , Zr 4+ and Ti 4+ . Secondary ion mass spectrometry study shows that the Ti 4+ ions follow a sum of two error functions in the width direction and a Gauss function in the depth direction of the waveguide. Both Er 3+ and Zr 4+ profiles follow the desired Gauss function, and entirely cover the Ti 4+ 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.

A number of Li-deficient MgO-doped LiNbO 3 (LN) crystals with different Li 2 O contents ranging from 43.4 mol. % to 44.5 mol. % were prepared by carrying out the Li-poor vapor transport equilibration treatment on 5 mol. % (in growth melt) MgO-doped LN crystals. Unclamped electro-optic (EO) coefficients γ 13 and γ 33 of these crystals were measured by Mach-Zehnder interferometry. The results show that γ 13 (γ 33 ) increases linearly by ∼14% (11%) as the Li 2 O content decreases from 44.5 mol. % of the as-grown state to 43.4 mol. % of the Li-deficient state. This feature is desired for the EO application of the Li-deficient MgO:LN crystal.

We report on a Ti-diffused near-stoichiometric (NS) LiTaO 3 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.

We report a near-stoichiometric Ti:Zr:LiNbO(3) strip waveguide fabricated from a congruent substrate with a technological process in the following sequence: Zr 4+ -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.

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.

Metasurfaces are engineered interfaces that contain a thin layer of plasmonic or dielectric nanostructures capable of manipulating light in a desirable manner. Advances in metasurfaces have led to various practical applications ranging from lensing to holography. Metasurface holograms that can be switched by the polarization state of incident light have been demonstrated for achieving polarization multiplexed functionalities. However, practical application of these devices has been limited by their capability for achieving high efficiency and high image quality. Here we experimentally demonstrate a helicity multiplexed metasurface hologram with high efficiency and good image fidelity over a broad range of frequencies. The metasurface hologram features the combination of two sets of hologram patterns operating with opposite incident helicities. Two symmetrically distributed off-axis images are interchangeable by controlling the helicity of the input light. The demonstrated helicity multiplexed metasurface hologram with its high performance opens avenues for future applications with functionality switchable optical devices.

We demonstrate the repeated utilization of self-assembled colloidal spheres for rapid nanopattern generations. Highly ordered micro-/nanosphere arrays were interlinked and confined by a soft transparent polymer (polydimethylsiloxane, PDMS), which can be used as light-focusing elements/photomasks for area-selective exposures of photoresist in contact. Because of the stiffness of the colloidal spheres, the photomasks do not encounter feature-deformation problems, enabling reliable production of highly uniform patterns over large areas. The geometrical feature of the patterns, including the size, pitch, and even the shape, can be finely tuned by adjusting the mask design and exposure time. The obtained patterns could be used as deposition or etching mask, allowing easy pattern transfer for various applications.

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.

A novel and simple Sm(3+)-doped-polymer/Ag/ SiO(2) trilayer structure was fabricated to investigate the impact of surface plasmon polaritons (SPPs) on the emission quantum efficiency of the dipole emitter Sm(3+). Photoluminescence (PL) enhancement factors for samples with different Ag thicknesses (30-70 nm) were found to be different when the thickness of the Sm(3+)-doped-polymer film was kept constant (220 nm). Theoretical analysis suggests that the electron density of the metal film plays an important role in the SPP assisted PL enhancement process, and this was confirmed in a Sm(3+)-doped-polymer/Ag/Au/ SiO(2) multilayer structure.

Efficient emission at 1.38 mum wavelength from holmium (Ho(3+))-doped low-phonon-energy gallate bismuth lead (GBL) oxide glasses, owing to the Ho(3+): ((5)S(2),(5)F(4))-->(5)I(5) transition, was observed, and the stimulated emission cross section was calculated to be 2.4x10(-21) cm(2). Population inversions between the ((5)S(2),(5)F(4)) and (5)I(5) levels have been achieved, and a broad gain bandwidth from 1350 to 1450 nm was obtained. The large product of emission cross section and measured lifetime also support this characteristic. The results indicate that a Ho(3+)-doped GBL glass system is a promising candidate for the development of E-band (1360-1460 nm) fiber-optic amplifiers.

Eu(TTFA)3-doped resin photoresist polymer film was successfully prepared and the fluorescence properties of the chelate complex were investigated. Based on Judd-Ofelt theory, the optical intensity parameters omega2 and omega4 derived from the emission spectrum were 24.4 x 10(-20) cm2 and 2.8 x 10(-20) cm2, respectively, and the total radiative transition rate (977 s(-1)) along with the radiative lifetime (1.02 ms) of the 5D(0) excited state were calculated. The stimulated emission cross sections sigma and the fluorescence branch ratios beta for the 5D(0) --> 7F(j) (J = 1, 2, 4) transitions were also obtained. The analysis indicates that the excited state of Eu3+ in the polymer film has a long radiative lifetime and large emission cross section, and the photoresist polymer film is a kind of ideal active amplificatory waveguide material, whose emission wavelength is in accord with the low absorption loss region of the photoresist. Such photoresist polymer film might have extensive application prospect in optical devices, such as polymer optical waveguide amplifiers and lasers.