Optical Dopants Research Articles

Evaluation of Structural, Morphological, Optical and Bactericidal Action of Branched Sm‐Doped CuO Nano‐Lanceolates

AbstractOver the years, metal oxides have been leveraged to create several intriguing novel antibacterial active materials such that while finding the ways and means to increase efficiency, rare earth elements are found to have often served as potential optical dopants such that an optimistic en route to achieve the same, branched Sm‐doped CuO nano‐lanceolates were synthesized employing a wet chemical approach. The samples were then annealed at three distinct temperatures, which were fixed to 300 °C, 400 °C, and 500 °C. The nano‐lanceolates have crystallized in the monoclinic phase, according to the XRD analysis. The SEM image of Sm‐doped CuO captured at a magnification of 2 μm reveals a branched morphology, with multiple nano‐lanceolates stacked in a stem. TEM image reveals that the width of a typical nano‐lanceolate attached to a stem and its tip are found to be 87 nm and 212 nm, respectively and the obtained EDS data validate that elements including Cu, Sm, and O are present in the doped sample. The UV‐visible spectra of the annealed samples indicate that the sample annealed at 300 °C (1.43 eV) has a larger band gap than the other samples. The sample that was annealed at 400 °C has endured defect emissions that are more intense than those of other samples, according to the obtained PL spectra. In addition to these fascinating findings, the samples annealed at 300 °C, 400 °C and 500 °C exhibit a zone of inhibition of 23 mm & 24 mm, 11 mm & 12 mm and 12 mm & 11 mm, respectively for the two tested bacterial strains which authenticate that the 300 °C annealed Sm‐doped CuO nano‐lanceolate deactivates the two pathogenic bacteria more effectively compared to the other samples. As a consequence, the Sm‐doped CuO nano‐lanceolates at 300 °C could potentially be an effective alternative for antibacterial materials, particularly in biomedical applications

Metallophthalocyanines as optical active dopants in borate glass

B2O3 – phthalocyanine composites (B2O3@MPc) were synthesized at 410 °C by sintering boron trioxide doped with base metal-free phthalocyanine (H2Pc) and/or its complexes of Mg, Zn, Gd (Pc = C32H16N8, phthalocyanine ligand, M = metal ion). The glassy products were characterized by scanning electron microscopy (SEM, EDS) and diffuse reflectance spectroscopy (DRS) which confirmed the incorporation of the respective phthalocyanines into the amorphous borate matrix. FTIR results suggested a possible impact of the phthalocyanine dopants on the final solid structure of the glassy matrix. The UV-excited composites emitted a pronounced blue phosphorescence featured by a two-step quenching process and lifetimes of 28 and 670 ms. Optical stimulated luminescence (OSL) tests proved excellent luminescence properties revealed by the samples including H2Pc and GdPc2 dopants. Reversible photoconductivity of the composites was confirmed by impedance spectroscopy measurements at current frequencies of 103 and 102 Hz and UV irradiation. The best results exhibited B2O3@GdPc2 featuring an impedance modulus decrease of about 2 orders of magnitude at 102 Hz compared to the other composites.

Optical nonreciprocal response and conversion in a Tavis‐Cummings coupling optomechanical system

We propose a scheme to realize optical nonreciprocal response and conversion in a Tavis-Cummings coupling optomechanical system, where a single cavity mode interacts with the vibrational mode of a flexible membrane with an embedded ensemble of two-level quantum emitters. Due to the introduction of the Tavis-Cummings interaction, we find that the phases between the mechanical mode and the optical mode, as well as between the mechanical mode and the dopant mode, are correlated with each other, and further give the analytical relationship between them. By optimizing the system parameters, especially the relative phase between two paths, the optimal nonreciprocal response can be achieved. Under the frequency domain, we derive the transmission matrix of the system analytically based on the input-output relation and study the influence of the system parameters on the nonreciprocal response of the quantum input signal. Moreover, compared with the conventional optomechanical systems, the Tavis-Cummings coupling optomechanical system exhibits richer nonreciprocal conversion phenomena among the optical mode, mechanical mode, and dopant mode, which provide a new applicable way of achieving the phonon-photon transducer and the optomechanical circulator in future practice.

Theoretical calculations and experimental investigations of lead phosphate glasses singly doped with Pr3+ and Tm3+ ions using luminescence spectroscopy

Abstract Lead phosphate glasses singly-doped with selected Ln3+ ions (Ln = Pr, Tm) were prepared by traditional melt-quenching method. The effect of concentration of optical active dopants in glass composition on spectroscopic properties of lead phosphate glasses were systematically investigated based on excitation, visible and near-infrared emission spectra as well as luminescence decay analysis. It was found that the luminescence intensity decreases with increasing content of Pr3+ and Tm3+ ions due to the concentration quenching. Also, the luminescence lifetimes of 1D2, 1G4 (Pr3+) and 1D2, 3H4 (Tm3+) states decrease with increasing concentration of both ions. Based on luminescence decay analysis and calculations using theoretical Inokuti-Hirayama model it was confirmed that non-radiative processes like cross-relaxation among the donor systems are dominate and influence direct donor-acceptor energy transfer in lead phosphate glasses. Moreover, the obtained results suggest clearly lower self-quenching emission in lead phosphate glasses doped with Pr3+ than Tm3+ ions.

Performance Enhancement of Chitosan Filled Silver Vanadate Nano-rods

Silver vanadate nanorods synthesized via chemical precipitation route at room temperature were characterized using UV/Vis. optical electronic spectra, fourier transform infrared (FTIR) spectroscopy, transmission and scanning electron microscopy (TEM, SEM), Zeta potential and X-ray diffraction (XRD). XRD indicates the presence of both β and α phases of silver vanadate. Chitosan samples filled with pre-calculated amounts of synthesized silver vanadate nano-rods were prepared via ordinary casting route. XRD of the prepared polymeric samples reveals amorphous nature and indicating a homogenous distribution of inorganic filler within the matrix without any tendency for crystallization. FTIR shows maintenance of chitosan characteristic bands in all samples. Optical energy gap for both direct and indirect transitions generally indicates a gradual decrease with increasing inorganic filler content. The biological activity against two-gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis), two gram-negative bacteria (Escherichia coli, Pseudomonas aeuroginosa) in addition to one fungus (Candida albicans) were also studied and correlated with both optical energy gap and nanoparticle dopant concentration.

Effects of optical dopants and laser wavelength on atom probe tomography analyses of borosilicate glasses

AbstractAtom probe tomography (APT) is a novel analytical microscopy method that provides three dimensional elemental mapping with sub‐nanometer spatial resolution and has only recently been applied to insulating glass and ceramic samples. In this paper, we have studied the influence of the optical absorption in glass samples on APT characterization by introducing different transition metal optical dopants to a model borosilicate nuclear waste glass. A systematic comparison is presented of the glass optical properties and the resulting APT data quality in terms of compositional accuracy and the mass spectra quality for two APT systems: one with a green laser (532 nm, LEAP 3000X HR) and one with a UV laser (355 nm, LEAP 4000X HR). These data were also compared to the study of a more complex borosilicate glass (SON68). The results show that the analysis data quality, particularly the compositional accuracy and sample yield, was clearly linked to optical absorption when using a green laser, while for the UV laser optical doping aided in improving data yield but did not have a significant effect on compositional accuracy. Comparisons of data between the LEAP systems suggest that the smaller laser spot size of the LEAP 4000X HR played a more critical role for optimum performance than the optical dopants themselves. The smaller spot size resulted in more accurate composition measurements due to a reduced background level independent of the material's optical properties.

Refractive index increase of acrylate‐based polymers by adding soluble aromatic guest‐molecules

This work presents the influence of dopants on viscosity in an uncured liquid state as well as on refractive index, Abbe number, optical loss, and glass transition temperature of different polymer compositions. The base material consists of Genomer 2263, a bisphenol, an epoxy diacrylate as matrix polymer, and benzyl methacrylate as comonomer. As dopants, the soluble aromatic guest‐molecules 9‐bromophenantrene and 9‐vinylcarbazole are investigated. The viscosity can be adjusted by different mixtures of the matrix polymer and comonomer from 3000 down to 4 mPa sec. Depending on the type and content of the dopants, the refractive index, Abbe number, and the glass transition temperature can be adjusted. The refractive indices increase linear at 589 nm and 20°C from 1.572 to 1.638 by doping, with Abbe numbers between 20 and 30. At this wavelength, the optical losses were determined to be around 2 dB · cm−1. The glass transition temperature can be tailored between 50 and 98°C. A way to use high amounts of optical dopants is presented, which opens up the way for different shaping technologies like inkjet printing of optical components. Copyright © 2016 John Wiley & Sons, Ltd.

(Invited) Computational Design of Lanthanide-Doped Optical Materials By a Combined DFT and Crystal-Field Approach: Recent Developments and Applications

In the last decades, lanthanide activated luminescent materials for lighting and display applications have been explored and optimized mainly by the cumbersome and costly trial-and-error experimental approach. Nowadays, the quick development of lanthanide spectroscopy theory together with an increase of the computational resources have made it possible to propose a systematical calculation strategy to understand the physics picture behind experiment and build up the link between the structural and optical properties of lanthanide-doped materials. It is well known that density functional theory (DFT) calculations employing the single-particle ground-state picture can provide very sufficiently accurate structural relaxation and the chemical trends that determine the emission energies and the luminescence mechanisms of optical dopants [1], whereas crystal-field (CF) theory calculations can very well reproduce experimentally observed optical spectra, which involve transitions between multi-electronic energy states of lanthanide ions [2]. Therefore, a combined theoretical scheme of modern DFT and conventional CF models has been proposed to give full play to their advantages [3]. In this talk, we will demonstrate how such a combined theoretical scheme supports the recent experimental studies of lanthanide phosphors. Ce3+ and Eu2+ ions will be paid more attention to due to their applications for white LED phosphors. The real reason resulting in the red or blue shift of the lowest 5d-4f emissions of Eu2+ or Ce3+ ions [4] will be analyzed by considering the combined effects of electronic structure and Stokes shift. Moreover, the misunderstanding about the position of the lowest 4f65d energy level in the 4f-5d excitation spectra of Eu2+ ions will be clarified, and thus the Stokes shift can be properly reproduced and further fed into understanding the electron-phonon coupling effect of Eu2+ ions with host lattices [5]. The successful application to the solid solution phosphors Ca2(Al1-x Mg x )(Al1-x Si1+x )O7: Eu2+will be shown in order to highlight the role of the theoretical work in the discovery of novel lanthanide phosphors [6]. Final, the recent developments and future challenges of the combined theoretical scheme will be given and commented, which include the first-principles structural determination of the 5d excited states of lanthanide ions and reproduction of the lowest charge transfer transition energy and its Stokes shift. Acknowledgements: The work is financially supported by National Natural Science Foundation of China (Grant No. 11204393), Natural Science Foundation Project of Chongqing (Grant No. CSTC2014JCYJA50034) and National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 201410617001).

Increasing pumping efficiency by using gradient-doped laser crystals

Investigations of a new class of optical materials with functional nonuniform distribution of optical dopant are continued. Longitudinal pumping and heat release in active elements with a gradient distribution of optical centers are simulated. It is shown that, for a given length of the laser element, pumping efficiency remains at a stably high level upon variation of its power density for different gradients of concentration of activators. It is demonstrated that, in addition to a high level of optical pumping efficiency, the temperature profile in the active medium becomes smoother.

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties.

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO₂) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.

Enhancement of blue photorefractive properties in Mg:Fe:Cu:SLiNbO3 crystals with near stoichiometry

Using the top seeded solution growth technique, near stoichiometric Mg : Fe : Cu : SLiNbO 3 crystals have been grown by using K 2 O as flux. Infrared transmission spectra were measured and defect structure and change of threshold value were investigated. Using Kr + laser as light source (blue light with wavelength of 476 nm) the photorefractive properties of crystals were measured. The diffraction efficiency of 76.3%, the short response time of 11 s, the dynamic range of 27.39, the sensitivity of 2.09 cm/J, and the refractive index change of 8.67 × 10-5 were obtained. The blue photorefractive properties were enhanced. As the holes are the dominant charge carriers, the short wavelength blue light which exhibits high energy can excite the holes from both of the shallow and the deep trap centers with the same phase. It was found that the so-called optical damage-resistant dopant such as Mg 2+ ions no longer functioned as the damage resistant at 476 nm wavelength, but turned to enhance the blue photorefractive characteristics.

Conformal Growth of Organic Luminescent Planar Defects within Artificial Opals

Herein, we present the result of combining, for the first time, the techniques of colloidal self-assembly and plasma-enhanced chemical vapor deposition to create a novel, high-quality, purely organic active photonic crystal structure of controlled optical properties. We show a fast, reliable, and accurate procedure to introduce two-dimensional luminescent organic defect layers within artificial polystyrene opals via a versatile room-temperature remote plasma deposition process. This method is gentle enough to allow highly conformal growth on polystyrene microspheres without altering their morphology or the ordered arrangement that they form. The luminescent organic layer behaves both as an optical dopant, causing the opening of transmission windows within the forbidden frequency interval of the lattice, and as an optically active material, whose emission can be tailored by the photonic environment.

Broadband enhancement of light emission in silicon slot waveguides

We investigate the light emission properties of electrical dipole emitters inside 2-dimensional (2D) and 3-dimensional (3D) silicon slot waveguides and evaluate the spontaneous emission enhancement (F(p)) and waveguide coupling ratio (beta). Under realistic conditions, we find that greater than 10-fold enhancement in F(p) can be achieved, together with a beta as large as 0.95. In contrast to the case of high Q optical resonators, such performance enhancements are obtained over a broad wavelength region, which can cover the entire emission spectrum of popular optical dopants such as Er. The enhanced luminescence efficiency and the strong coupling into a limited set of well-defined waveguide modes enables a new class of power-efficient, CMOS-compatible, waveguide-based light sources.

Segregation during crystal growth from melt and absorption cross section determination by optical absorption method

Segregation during crystal growth from melt under two conditions is studied by using crystal mass, which can be measured easily, as an independent variable, and a method to determine the effective segregation coefficient and absorption cross section of optical dopant is given. When the segregated solute disperses into the whole or just a part of melt homogenously, the concentration Cs in solid interface will change by different formulas. If the crystal growth interface is conical and segregated solute disperses into melt in total or part, the solute concentration at r = 2/3R, where r is the distance from the growth cross section center and R the crystal radius, is independent on the shape of the crystal growth interface, and its variation at r = 2/3R can be regarded as the result from crystal growth in flat interface. With Cs variation formula in solid and absorption cross section σ for optical dopant, the absorption coefficients along the crystal growth direction can be calculated, and the corresponding experimental value can be obtained through the crystal optical absorption spectra. By minimizing the half sum, whose independent variables are k, ΔW or σ, of the difference square between the calculated and experimental absorption coefficients from one or more absorption peaks along the crystal growth direction, k and σ, or k and ΔW, can be determined at the same time through the Levenberg-Marquardt iteration method. Finally, the effective segregation coefficient k, ΔW and absorption cross sections of Nd:GGG were determined, the results fitted by two formula gave more closed effective segregation coefficient, and the value ΔW also indicates that the segregated dopant had nearly dispersed into the whole melt. Experimental results show that the method to determine effective segregation coefficient k, ΔW and absorption cross sections σ is convenient and reliable, and the two segregation formulas can describe the segregation during the crystal growth from melt relatively commendably.

Optical Fiber Drawing and Dopant Transport

Optical fibers are made of glass with different refractive indices in the (inner) core and the (outer) cladding regions. The difference in refractive indices arises due to a rapid transition in the concentration of a dopant across the boundary between these two regions. Fibers are normally drawn from a heated glass preform, and the different dopant concentrations in the two regions will change due to dopant diffusion and convective transport induced by the flow. In this paper, we analyze a mathematical model for the dynamics of dopant concentration changes during the fiber drawing process. Using a long-wave approximation, we show that the governing equations can be reduced to a simple diffusion equation. As a result, we are able to identify key dimensionless parameters that contribute to the diffusion process. We also derive asymptotic solutions for the temperature, cross-sectional area, and effective diffusion coefficient when there are strong temperature dependencies in the viscosity and the diffusion coefficient. Our simplified model and asymptotic solutions reduce the need for extensive numerical simulations and can be used to devise control strategies to limit excess dopant diffusion.

Enhanced Photoconductivity in Thin‐Film Semiconductors Optically Coupled to Photonic Crystals

Photonic crystals (PCs) are a remarkable class of materials wherein the periodicity of the index of refraction can be engineered to obtain unprecedented optical properties that have no parallels in other materials. Some interesting optical phenomena inherent to PCs include second harmonic generation, the superprism effect, photonic bandgaps (PBGs), and “slow photons”. It is also possible to achieve light localization within PCs by introducing defects by design that disrupt the periodicity of the index of refraction, allowing the creation of localized photon modes having frequencies that lie within the PBG of the PC. The ability of defect modes in PCs to confine photons is expected to provide the infrastructure for optical circuits. Moreover, lossless light propagation along PBG waveguides with coupling to quantum dots or optical cavities could provide new avenues for quantum information processing. Considering that an ideal crystal is a periodic structure extending to infinity in all directions, the planar surface of a PC can actually be regarded as a 2D crystal defect. Accordingly, it is interesting to note that as in the case of defects introduced into the bulk of a PC, light can also be localized at the PC surface. For instance, it has been known for quite some time that light can propagate in localized modes along the surface of a periodically layered medium, which effectively acts a 1D PC. Recently, Miguez and co-workers have investigated photon surface resonant modes in thin films coupled to PCs. One structure studied in this work has been fabricated by depositing a homogeneous silica layer on top of a silica inverse colloidal crystal. The results of the study indicate that upon illumination of this layer of silica with normally incident light at certain frequencies within the bandgap of the PC, the electromagnetic field near the PC/film interface is amplified with respect to the electromagnetic fields in the surrounding regions. This phenomenon arises from partial light localization at the modified PC surface, which behaves as an optical dopant or defect. Structures similar to those studied by Miguez and co-workers have been used to enhance the efficiency of Gratzel cells comprising dye-sensitized titania electrodes shaped as PCs. The observed improvements were initially attributed to slow photons propagating through the PC structure; however, it has subsequently been pointed out that this hypothesis does not account for all of the observed results and that the improvements arise primarily from light localization at the surface of the structure. The objective of the research reported herein is two-fold. The first objective is to demonstrate that the photoconductivity of a semiconductor film can be amplified by optically coupling the film to a PC surface. Indeed, in this construct, the film does not itself need to be periodically structured. The second objective is to show that the photoconductivity enhancement attainable from surface resonant modes in thin films coupled to PC surfaces is greater than the enhancement that can be achieved by depositing a perfect mirror (PM) onto the backside of this film. To address the first objective, we have compared the measured quantum efficiencies (QEs) of a thin hydrogenated amorphous silicon (a-Si:H) film deposited on a glass substrate for two different structures. One structure is the film–PC construct shown in Figure 1a, wherein an opaline PC is deposited onto the backside of a thin a-Si:H film, whereas the secC O M M U N IC A IO N

Studies on third-order nonlinear optical properties of chalcone derivatives in polymer host

In this paper we present the experimental study of the third-order nonlinear optical properties of two chalcone derivatives, viz., 1-(4-methoxyphenyl)-3-(4-butyloxyphenyl)-prop-2-en-1-one and 1-(4-methoxyphenyl)-3-(4-propyloxyphenyl)-prop-2-en-1-one in PMMA host, with the prospective of reaching a compromise between good processability and high nonlinear optical properties. The nonlinear optical properties have been investigated by Z-scan technique using 7 ns laser pulses at 532 nm. The nonlinear refractive index, nonlinear absorption coefficient, magnitude of third-order susceptibility and the coupling factor have been determined. The values obtained are of the order of 10 −14 cm 2/W, 1 cm/GW, 10 −13 esu and 0.2, respectively. The molecular second hyperpolarizability for the chalcone derivatives in polymer is of the order of 10 −31 esu. Different guest/host concentrations have also been studied. The results suggest that the nonlinear properties of the chalcones have been improved when they are used as dopants in polymer matrix. The nonlinear parameters obtained are comparable with the reported values of II–VI compound semiconductors. Hence, these chalcons are a promising class of nonlinear optical dopant materials for optical device applications.

Anhydrous Sol-Gel Synthesis of Titania-Doped Siloxane Polymer for Integrated Optics

Sol-gel synthesis of organic-inorganic hybrid materials for planar waveguides and devices has received growing interest due to its low-cost processing and good suitability for doping. Titania is an important optical dopant, but homogeneous incorporation of titania in silica is difficult to be achieved by the conventional sol-gel process (aqueous system) because of the significant difference between the hydrolysis rates of the precursors. In this paper, we report an anhydrous sol-gel process for synthesising titania-doped siloxane polymers. The process consists of a hydrolysis of 3-methacryloxypropyltrimethoxysilane (MPS) with boric acid under anhydrous conditions, and a condensation with dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET). Optical characterisations for the produced titania-doped polymer were performed, and results showed that TET doping is useful for reducing the OH concentration of the synthesised polymer and is also effective for improving the optical quality of spin coatings. DMDMS and DPhDMS are favourable in reducing the birefringence and in increasing the thermostability of the material, and the methacryl groups of MPS are UV-polymerizable, which is useful for low cost fabrication of waveguides by photolithographic process. The results of ellipsometry scanning measurements show that titania is homogeneously incorporated in the hybrid matrix, suggesting that the anhydrous sol-gel process is useful for preparation of UV-sensitive titania-doped siloxane polymers for optical applications.

Excitation paths in RE-doped III–V semiconductors

Optical properties of III–V compound semiconductors are frequently engineered by doping with RE ions. In that way narrow emission bands with a temperature-independent wavelength can be obtained. In order to achieve intense luminescence, efficient and temperature-stable excitation mechanism, as well as suppression of nonradiative recombinations of the optical dopant is required. Investigation of these processes is usually done by analysis of thermal effects and by excitation spectroscopy. Recently, we have proposed that energy transfer mechanisms in optically doped semiconductor hosts can be conveniently studied using two-color experiments combining band-to-band pumping with spectral probing by a free-electron laser as a tunable source of mid-infrared radiation. In this paper, we review shortly some results obtained by this novel approach on InP:Yb, and discuss perspectives of future research.

Two-color mid-infrared spectroscopy of optically doped semiconductors

Optical doping is an attractive method to tailor photonic properties of semiconductor matrices for development of solid-state electroluminescent structures. For practical applications, thermal stability of emission obtained from these materials is required. Thermal processes can be conveniently investigated by two-color spectroscopy in the visible and the mid-infrared. Free-electron laser is a versatile high-brilliance source of radiation in the latter spectral range. In this contribution, we briefly review some of the results obtained recently by the two-color spectroscopy with a free-electron laser in different semiconductors optically doped with rare earth and transition metal ions. Effects leading to both enhancement and quenching of emission from optical dopants will be presented. For InP:Yb, Si:Er, and Si:Cu activation of particular optically induced non-radiative recombination paths will be shown. For Si:Er and Si:Ag, observation of a low temperature optical memory effect will be reported.