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Two-dimensional holographic structures based on photopolymer compositions with luminescent nanoparticles, such as quantum dots, are promising candidates for multiresponsive luminescence sensors. However, their applicability may suffer from the incompatibility of the components, and hence aggregation of the nanoparticles. We showed that the replacement of an organic shell at the CdSe/ZnS quantum dots' surface with monomer molecules of the photopolymerizable medium achieved full compatibility with the surrounding medium. The effect was demonstrated by luminescence spectroscopy, and steady-state and time-resolved luminescent laser scanning microscopy. We observed the complete spectral independence of local photoluminescence decay, thus proving the absence of even nanoscale aggregation, either in the liquid composition or in the nodes and antinodes of the grating. Therefore, nanostructured luminescent photopolymer gratings with monomer-covered quantum dots can act as hybrid diffractive–luminescent sensor elements. [ABSTRACT FROM AUTHOR]

The structurization of holographic planes in holograms recorded in CaF 2 crystal with color centers was found. It is apparent in the formation of spiral bundles, which pierce the holographic planes. It testifies to the self-organization process of color centers in these planes. This process is supposed to be linked with colloidal centers, 2D metal islets in the crystal lattice, whose formation and decay on hologram recording at temperatures of 150–190 °C may be considered as a dynamic phase transition that facilitates the generation of stable spatially inhomogeneous (dissipative) structures in the form of bundles. They arise on hologram recording and are frozen on cooling of the crystal after the recording process is finished. [ABSTRACT FROM AUTHOR]

• Composite material based on porous glass and As 2 S 3 nanolayers was fabricated. • This composite exhibits giant, reversible photo-induced bleaching effect. • These changes could be connected with optical and structural effects in As 2 S 3. • Partially the processes could be attributed to the confinement effect of nanopores. • The As 2 S 3 -porous glass composites can be useful for 3D optical-structural patterns. Novel composite material based on silica porous glass as low refractive index matrix and high refractive index As 2 S 3 nanoparticles filled in the pores has been made. Chalcogenide nanoparticles were dissolved and the porous glass matrix was impregnated in the obtained solution. Subsequently, the solvent was evaporated by annealing the porous glass. Various optical parameters of the created composite material are presented in this paper. These parameters are based on optical and structural transformations which occur under active illumination and heat treatment in such chalcogenide-containing composite and compared with thin As 2 S 3 light-sensitive layers. New functionalities may be added this way to the composite, such as illumination and/or thermally driven optical parameters. Developing and optimizing the optical properties of the obtained As 2 S 3 -porous glass composites can be useful for creating 3D optical-structural patterns for different applications such as holographic data storage, light modulation, and/or functional, nonlinear optical elements with various parameters for VIS-NIR optics. [ABSTRACT FROM AUTHOR]

Magnetic-luminescent composites based on semiconductor quantum dots (QDs) and superparamagnetic iron oxide nanoparticles (SPIONs) can serve as a platform combining visualization and therapy. Here, we report the construction of QD-SPION nanocomposites based on synthesized SPIONs and alloyed QDs (Cd x Zn 1 − x Se y S 1 − y) / ZnS solubilized with L-cysteine molecules. The study of the spectral-luminescence characteristics, the kinetics of luminescence decay show the composite's stability in a solution. After incubation with HeLa cells, QDs, SPIONs, and their composites form clusters on the cell surface and associate with endosomes inside the cells. Component-wise analysis of the photoluminescence decay of cell-associated QDs/SPIONs provides information about their localization and aggregate status. [ABSTRACT FROM AUTHOR]

A new approach to the formation of colloidal nanocomposites based on CdSe/ZnS quantum dots and monomeric form of Chlorin e6 is suggested. We demonstrate that FRET with efficiency close to theoretical prediction can be realized in the nanocomposites, and it leads to twofold enhancement of singlet oxygen generation in comparison with the same amount of free Chlorin e6. [ABSTRACT FROM AUTHOR]

We devote this article to the spectral analysis of volume holograms recorded in materials with diffusion-based formation mechanisms. Two media of different natures were examined: polymer material with dye molecules photoattachable to macromolecules (PQ-PMMA) and photochromic additively colored fluorite crystal (CaF2). Differential spectra of holograms refractive index and absorbance were determined by two approaches: numerical approximation of both spectral and angular hologram response (selectivity hypercontour) by coupledwave theory and processing hologram spectra by Kramers-Kronig dispersion relations. The principles of the two approaches, results of their application, and advantages and disadvantages are discussed. Kramers-Kronig relations can be usefully applied in cases where the nature of holograms formation is well studied, whereas the hypercontour approach is indispensable for obtaining the values of absorbance and refractive index modulation; therefore, a combination of both the techniques is a powerful tool for fundamental investigation of the hologram formation mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: The effect of temperature on luminescence of semiconductor nanocrystals is used for monitoring local heating of specimens studied at laser scanning microscope. The spectral position of luminescence maximum is a convenient parameter to be followed; its thermal shift remains nearly linear within a broad temperature range. Nanoplatelets are found advantageous nanosized temperature sensors as compared to quantum dots due to narrower luminescence spectrum. [ABSTRACT FROM AUTHOR]

Abstract: Luminescent images of a few distinguishable alloyed semiconductor quantum dots obtained at room temperature using confocal scanning microscopy with spectral and temporal resolution demonstrate blinking of spatially distinguishable spots and local luminescence spectra varying within the ensemble. [ABSTRACT FROM AUTHOR]

Nonlinear recording of stable fluorescent microstructures in PMMA films doped with photosensitive compound 2-(furan-2-yl)-3-(thiophen-2-carbonyl)-chromen-4-one is investigated. Energy and power density thresholds for recording stable fluorescent marks and for film destruction and photobleaching of the fluorescent marks by laser pulses were measured in wide spectral (from 530 to 620 nm) and temporal (from 80 to 7 ns) ranges. The evidences of the sequential two-step excitation mechanism for the studied dye are presented. It was shown that picosecond pulse duration range is preferable for two-photon data recording. Quasi-Gaussian and donut shaped fluorescent marks with almost the same cross-section were recorded by femtosecond pulses with rather small difference in energies. [ABSTRACT FROM AUTHOR]

[Display omitted] • MicroCoat® coated AISI 304 steel topography was modified by nanosecond laser pulses at variable incident laser fluence. • The water-wetting angles continuously decreased from 100° to 10° on the patterned surfaces. • The autonomous directional water flow was demonstrated on the laser-structured patterns of various shapes. • Temporal tracking of the contact angle after the laser structuring demonstrated gradual surface hydrophobization. A series of hybrid textures with variable topography and chemical composition were obtained on a hydrophilic steel (AISI 304) substrate with a hydrophobic MicroCoat® coating at the increasing incident nanosecond laser fluence from 1.4 J/cm2 to 5.6 J/cm2. The microtopography of the textured surface was studied by laser microscopy and scanning electron microscopy (SEM), while the chemical composition of the surface was determined by IR spectroscopy. The contact angles of water wetting in the textured areas varied versus laser fluence from about 100° to 10°, which was explained by both ablative removal of the hydrophobic polymer coating and the increase in roughness of the hydrophilic steel surface. The time dependence of the contact angle on the different textures, which demonstrated hydrophobization at different time scales depending on the texturing conditions, was analyzed. Autonomous directional flow was observed on laser-patterned wetting-gradient structures of various shapes, and the flow velocity of water droplets on these structures were measured. It was shown that the velocity of water drop spreading on the gradient structures depends on the difference in contact angles on adjacent spots. The various modules fabricated can be harnessed in chemical and biomedical microfluidic devices. [ABSTRACT FROM AUTHOR]

Mixed-conducting La0.3Sr0.7Co0.8Ga0.2O3-δ (LSCG) possesses substantial oxygen permeability, but exhibits a high activity to complete CH4 oxidation, thus making it necessary to incorporate reforming catalysts in the membrane reactors for methane conversion. Dominant CO2 formation is observed for the steady-state conversion of CH4 by atmospheric oxygen (methane/air ratio of 30:70) in a fixed bed reactor with LSCG as catalyst, and for the oxidation of CH4 pulses supplied in helium flow over LSCG powder. The conversion of dry CH4 by oxygen permeating through dense LSCG ceramics, stable operation of which under the air/CH4 gradient is possible due to the surface-limited oxygen transport, yields CO2 concentrations higher than 90%. The prevailing mechanism of total methane combustion is probably associated with weak Co–O bonding in the perovskite-related LSCG lattice, in correlation with data on oxygen desorption, phase stability and ionic transport. [Copyright &y& Elsevier]

Highly doped (20 at.%) Yb3+:LiYF 4 single-crystalline thin films are grown on (001)-oriented bulk undoped LiYF 4 substrates by Liquid Phase Epitaxy using lithium fluoride (LiF) as a solvent. The growth temperature lies around 741 °C (0.5–1 °C supercooling) and the growth rate is 1.8–2.6 μm/min. The single-crystalline nature of the films is confirmed by X-ray diffraction and polarized Raman spectroscopy. The film morphology is studied and discussed. The polarized spectroscopic properties of Yb3+ ions are reported, indicating a stimulated-emission cross-section of 0.88 × 10−20 cm2 at 993.9 nm in π-polarization and a radiation trapping free lifetime of the 2F 5/2 state of 2.00 ms indicating weak concentration-quenching. The crystal-field splitting of Yb3+ multiplets is resolved at 12 K. Highly-doped Yb3+:LiYF 4 /LiYF 4 homoepitaxies are promising for waveguide and thin-disk lasers at ~1 μm. • Liquid Phase Epitaxy growth of 20 at.% Yb:LiYF 4 films on oriented LiYF 4 substrates. • The films crystallize in tetragonal system with a = 5.157 Å and c = 10.714 Å. • Polarized Raman spectra are measured: the maximum phonon energy is 444 cm−1. • The stimulated-emission cross-section is 0.88 × 10−20 cm2 at 993.9 nm in π-polarization. • The crystal-field splitting of Yb3+ multiplets is resolved at 12 K. [ABSTRACT FROM AUTHOR]

Water-soluble nanocomposites based on CdSe/ZnS quantum dots (QDs) and hydrophobic tetraphenylporphyrin (TPP) molecules passivated by chitosan (CS) have been formed. Magnetic circular dichroism (MCD) spectra evidence TPP presence in both monomeric and agglomerated forms in the nanocomposites. The nanocomposites demonstrate more pronounced singlet oxygen generation compared to free TPP in CS at the same concentration due to the intracomplex Förster resonance energy transfer (FRET) with a 45% average efficiency., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report on the first, to the best of our knowledge, in-band pumped T m codoped waveguide (WG) laser. A depressed-index surface channel WG (type III) with a 50 µm half-ring cladding is fabricated in a 5 at. % 3+ , H o 3+ codoped waveguide (WG) laser. A depressed-index surface channel WG (type III) with a 50 µm half-ring cladding is fabricated in a 5 at. % T crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, m 3+ , 0.5 at. % H o 3+ ) is 448 mW with a slope efficiencyM of 40.6%, which is a record high for this type of WG lasers. The maximum output power of the Ho laser reaches 144 mW.K L u ( W O 4 ) 2 crystal by femtosecond pulse direct laser writing. Under in-band pumping by a 1679 nm Er Raman fiber laser, T m 3+ and H o 3+ colasing is observed in the WG and explained by bidirectional energy transfer. The maximum total output power at ∼1942 n m ( T m 3+ ) and 2059 nm ( H o 3+ ) is 448 mW with a slope efficiencyM of 40.6%, which is a record high for this type of WG lasers. The maximum output power of the Ho laser reaches 144 mW.

Surface channel waveguides (WGs) based on a half-ring (40-60-µm-diameter) depressed-index cladding (type III) geometry are fabricated in monoclinic Tm 3+ :MgWO 4 by femtosecond (fs) laser writing at a repetition rate of 1 kHz. The WGs are characterized by confocal laser microscopy and μ -Raman spectroscopy. A Tm 3+ :MgWO 4 WG laser generates 320 mW at ∼2.02µm with a slope efficiency of 64.4%. The WG emits a transverse single-mode and linear polarization ( E || N ). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at ∼2.08µm is also achieved.m ). A remarkable low loss of <0.1dB/cm is measured for the WG. Vibronic laser emission at ∼2.08µm is also achieved.

Depressed-index buried and surface channel waveguides (type III) are produced in a bulk 3.5 at.% Tm 3+ :CALGO crystal by femtosecond direct-laser-writing at kHz repetition rate. The waveguides are characterized by confocal microscopy and µ-Raman spectroscopy. Under in-band-pumping at 1679 nm ( 3 H 6 → 3 F 4 transition) by a Raman fiber laser, the buried channel waveguide laser with a circular cladding (diameter: 60 µm) generated a continuous-wave output power of 0.81 W at 1866-1947 nm with a slope efficiency of 71.2% (versus the absorbed pump power) and showed a laser threshold of 200 mW. The waveguide propagation losses were as low as 0.3 ± 0.2 dB/cm. The laser performance under in-band pumping was superior compared pumping at ∼800 nm ( 3 H 6 → 3 H 4 transition), i.e., the convetional pump wavelength. Vibronic laser emission from the WG laser above 2 µm is also achieved. The low-loss behavior, the broadband emission properties and good power scaling capabilities indicate the suitability of Tm 3+ :CALGO waveguides for mode-locked laser operation at ∼2 µm.

We report on efficient laser operation of the first holmium monoclinic double tungstate waveguide laser fabricated by femtosecond direct laser writing. A depressed-index buried channel waveguide with a 60 μm diameter circular cladding was inscribed in 5 at.% Ho 3+ :KGd(WO 4 ) 2 . It was characterized by confocal microscopy and μ-Raman and μ-luminescence spectroscopy, indicating well-preserved crystallinity of its core. Pumped by a thulium bulk laser, the holmium waveguide laser generated 212 mW at 2055 nm with a slope efficiency of 67.2%. The waveguide propagation losses were 0.94±0.2  dB/cm.

We report the generation of mid-infrared (~2 µm) high repetition rate (MHz) sub-100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS 2 . The waveguide (propagation losses of ~1 dB/cm) was micro-fabricated by means of ultrafast femtosecond laser writing. In the continuous-wave regime, the waveguide laser generated 247 mW at 1849.6 nm with a slope efficiency of 48.7%. The laser operated at the fundamental transverse mode with a linearly polarized output. With graphene as a saturable absorber, the pulse characteristics were 88 ns / 18 nJ (duration / energy) at a repetition rate of 1.39 MHz. Even shorter pulses of 66 ns were achieved with MoS 2 . Graphene and MoS 2 are therefore promising for high repetition rate nanosecond Q-switched infrared waveguide lasers.

We report on the first erbium (Er 3+ ) doped double tungstate waveguide laser. As a gain material, we studied a monoclinic Er 3+ :KLu(WO 4 ) 2 crystal. A depressed-index buried channel waveguide formed by a 60 µm-diameter circular cladding was fabricated by 3D femtosecond direct laser writing. The waveguide was characterized by confocal laser microscopy, µ-Raman and µ-luminescence mapping, confirming that the crystallinity of the core is preserved. The waveguide laser, diode pumped at 981 nm, generated 8.9 mW at 1533.6 nm with a slope efficiency of 20.9% in the continuous-wave regime. The laser polarization was linear (E || N m ). The laser threshold was at 93 mW of absorbed pump power.