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Plasmons in graphene are known to be tunable and to exhibit extreme field confinement, making them useful for optoelectronic devices, and for exploring extreme light matter interactions. Thus far, these effects have been demonstrated at Thz to mid-IR frequencies, with the upper frequency limit set by limits of electron beam lithography, which can make graphene nanostructures as small as 15nm. In this talk, I will show that bottom-up block co-polymer lithography methods can create nanostructures with characteristic lengthscales as small as 12nm, and that in this regime the non-local interactions in graphene become strong, creating a significant blue shift of the plasmonic resonances. This allows for the creation of plasmonic cavities with resonances at wavelengths as short as 2.2um. The confinement factors of these cavities reach 135, which is exceedingly large, but less than what has been predicted by theory.

The capping layer (CL) overgrowth process is a very mandate step to preserve the quantum dot (QD) basic parameters necessary for enhanced device performance. It is a well-known aspect that the strain fields inside QD(CL) gets altered both along [100] (perpendicular) and [001] (parallel) directions, when employed with an appropriate CL thickness and composition (%). In this study, we report on the InAs Sub-monolayer (SML) QDs capped by a tensile-strained CL: GaAs1−xNx (2 ML thick), to lessen the net compressive strain in the system. A 8-band k.p simulation was performed in this regard to understand the change in optical and strain properties, for varying dilute Nx contents (x): 1.5, 1.8, 2.2 and 2.5% respectively. Firstly, the hydrostatic (biaxial) strain along [001] inside QD region increases (decreases) with increasing x(%) and this supposedly should blueshift photoluminescence (PL) spectra. Secondly, the changes in band structure across the conduction and valence bands (CB, VB) gave some clear insights on the PL redshift. The CB minima in CL gets lowered, accounting for reduced carrier confinement and not due to the strain counterparts. The tensile strain nature of CL has a larger band gap bowing parameter that helps in this stronger redshift in PL energy. By this lowering of CB energy in CL, the electron eigen levels inside QD shift downwards, reducing the bandgap of the same. Finally, the simulated PL energy values at 19 K for varying N% was found to be 1.06, 1.02, 0.96, and 0.92 eV finding it suitable for laser applications.

The cultures of filamentous fungi in aquatic medium release fluorescent metabolites (FM) with emission spectra that closely match the typical fluorescence bands found for soil extracts and aquatic fluorescent dissolved organic matter (FDOM). FM released from some fungal cultures show as well comparable values of fluorescent quantum yield, the blue shift of emission spectra excited in the UV, and a very close match of ultraviolet–visible absorbance spectral curves related to soil and aquatic FDOM, further strengthening the similarity of fluorophores in those aquatic material. Given the importance of microscopic filamentous fungi in the global carbon cycle, our results indicate that filamentous fungi are likely to be important sources of aquatic and soil FDOM of microbial origin.

Carbon dots are unique fluorescent nanoparticles that can be made of many carbon sources. However, carbon source such as plastic is difficult to make carbon dots using simple synthesis procedure due to strong carbon bonds in the plastic material. The utilization of plastic source in carbon dots is a challenge. In this work, we used polyethylene in synthesis of citric acid carbon dots using simple microwave technique. We studied the effect of polyethylene addition on optical properties and surface energy level of carbon dots. We found that absorbance peak of core carbon dot was red shift and absorbance peak of surface level was blue shift due to addition of polyethylene. However, photoluminescence and timeresolved photoluminescence measurements showed that surface energy level was red shifted due to addition of polyethylene. The change of surface functional group was clearly observed using infra-red spectroscopy. Therefore, addition of polyethylene in carbon dots clearly modified surface energy level of carbon dots.

The LEDs were obtained that the peak emission wavelength and FWHM were 665 nm and 67 nm at 20 mA, respectively. It exhibited a large blueshift of the EL peak wavelength from 691 nm at 5 mA to 631 nm at 100 mA. In this range, the blue-shifted value was 60 nm. Besides, we realized the single peak emission LEDs without an additional emission. We obtained a light output, forward voltage, and EQE of 0.07 mW, 2.45 V, and 0.19% at 20 mA, respectively. The LEDs exhibited the temperature stability of EL intensity and peak wavelength.

In this paper, we experimentally and theoretically analyse the formation and interaction of dark solitons in a long laser. The laser includes a semiconductor optical amplifier (SOA), centred around 1300nm, an intracavity filter and a fibre cavity whose length can vary from 20m to 20km. Near the lasing threshold the laser exhibits slowly evolving power dropouts the circulate the cavity. These dropouts are associated with the formation of Nozaki-Bekki Holes (NBH), also referred to as dark solitons. We observe both experimentally and numerically that the core of these holes exhibit chaotic dynamics and emit short light pulses. These pulses are found to be blue shifted with respect to the frequency of the dark solitons and therefore travel with a faster group velocity. These pulses are strongly damped, as they are detuned with respect to the filter transmission, but they may lead to the creation of new dark solitons. These pulses also play a major role in the development of optical turbulence when the filter is set at a frequency above 1310nm. In this case, the laser displays numerous dark solitons per round trip and the fast travelling pulses act as an interaction between the solitons, which can lead to the development of defect mediated turbulence.

Light emission from PbS quantum dots (QDs) is an intriguing topic from application perspectives, and even after myriad of articles, still has open questions. The paper highlights the optical characterization of PbS QDs deposited via solvent deposition on semi-insulating GaAs substrates. The QD thin films were characterized by two-photon excited photoluminescence (TPL) measurements, exciting the samples with increasing pulsed laser (1064 nm, 10 Hz, 26 ps) intensities. The work reveals alterations of the optical properties of GaAs when hetero-paired with PbS QDs, as demonstrated by the trend of the TPL peak increase, the energy where the TPL peak takes place, and the overall dynamics of the peak shift. We also report that the TPL intensity increase of PbS QDs shows the same trend as the single-photon excited emission, and observed photo-induced doping of the QDs, i.e., the dynamic Burstein-Moss blue shift. The work stresses the possibility to modify the optical properties of semiconductor hosts by means of heteropairing with QDs. Through this work, we further attempt to reconcile observations, which are much different from reported classical models in semiconductor heterostructures.

The Institute for Astrophysics Gottingen operates a solar observatory that combines a 50 cm siderostat with (1) a vacuum vertical telescope, (2) a very high resolution Fourier Transform Spectrograph (R < 900, 000 at 600 nm), and (3) a Laser Frequency Comb for extremely precise and accurate frequency calibration (< 10 cm/s). We introduce our setup that feeds the spectrograph with either a 32.5” field of view of the solar surface, or with disk-integrated sunlight for Sun-as-a-star observations and explain the necessary computational steps to guide specific positions on the solar surface into the fiber. Our instrument suite can deliver spectroscopic measurements with extremely accurate frequency calibration, which is valid across very large frequency regions (approx. 400-800 nm in wavelength). This allows precision spectroscopy of individual lines in order to study the variability of spectral lines in Sun-as-a-star observations as well as determining the convective blueshift across the solar surface from many spectral lines.

Liquid crystal materials don’t emit light, and its phase difference is connections with viewing angle. In general, the brightness of liquid crystal displays (LCD) is limited and the color shift apparently exists at large viewing angles. Furthermore, the same problem is also emerged in organic light emitting diode (OLED) displays. Microcavity resonance effect in OLED seriously affects the luminance and brings about “blue shift” as viewing angle increases. We propose an optical film with micro-prism to improve the viewing angle characteristics of LCD and OLED, which can increase the brightness and decrease the color shift. Excellent agreements supported by simulations and experiments are obtained. The proposed optical film is coated on a 75in. 8K (7680×4320) LCD to measure the optical parameters. When the viewing (polar) angle is between ±60° and a white pattern is displayed, the maximum color shift Δμ'v' can be decreased from 0.027 to 0.006 after the proposed optical film is introduced. Moreover, the brightness at large viewing angles is enhanced obviously, both theoretical and experimental results are proved that the luminance is about 5%~40% higher than previous when the viewing angle ranges from 30° to 60° correspondingly.

An unsolved problem of mixed halide perovskites is the light induced compositional instability. Under illumination microscopic clusters with a higher iodide content form which act as efficient recombination centers reducing device performance. In photoluminescence measurements this leads to the development of a secondary peak at low energies that increases in intensity and shifts towards lower energies. Different theories for about the origin have been developed but the underlying key mechanisms are still under debate. In the presented study the photoluminescence evolution of MAPb(I1.5Br1.5) perovskites with varying microstructure is investigated at various excitation densities and temperatures. We find a more evolved segregation mechanism with an intermediate stage between the commonly reported mixed phase and the appearance of the I-rich clusters (Br content < 50%). In this intermediate stage perovskite domains with nearly pure iodide content form (Br content < 25%). Using low excitation densities, the interplay between the I-rich domains and the I-rich clusters leads to a blue shift of the conjunct I-rich luminescence peak. At high excitation densities the I-rich domains and the I-rich clusters are clearly distinguishable, due to a stronger PL response of the I-rich domains. With continuous illumination more I-rich cluster form acting as carrier traps and recombination centers. Due to this, the influence of the few I-rich domains on the PL signature decreases leaving only the commonly reported red shift of the I-rich clusters at later stages of the segregation. The formation of the I-rich domains is fully reversible in the dark and occurs also at elevated temperatures. Measurements on sample with varying grain size further indicate an enhanced formation of those I-rich domains on samples with high grain boundary density possibly by a faster halide mobility along them.

This study is focused on structural and optical properties of multilayer InAs/InGaAs dot-in-a-well (DWELL) heterostructure with varying capping layer thickness. Two samples A and B are considered with 2 monolayer (ML) InAs quantum dots (QDs). The top InGaAs capping layer thickness is varied from 6 to 8 nm from sample A to B, whereas the lower well thickness was kept constant at 2 nm. The ground-state peak in the photoluminescence (PL) spectra shows a blue shift with increased capping layer thickness (sample A: 1148 nm, sample B: 1140 nm). This blue shift is due to the increased well layer thickness, which leads to higher strain and shrinkage in dot size. The activation energy (Ea) is calculated from the temperature dependent PL results using the Arrhenius equation. The activation energy of sample A and B are 181 meV and 152 meV respectively. The higher activation energy leads to a reduction in dark current, which affirms that sample A would be better for the device application. Raman spectroscopy is also carried out to observe different phonon peaks in both samples. For sample B, the broadening of the GaAs transverse optic (TO) mode is higher, which may lead to increased non-radiative carrier recombination. It may also lead to reduction of carrier lifetime. Hence, sample A with lower well thickness would be useful in optoelectronic device application because of its improved optical characteristics.

The strain-coupled InAs Stranski-Krastanov (SK) and submonolayer (SML) quantum dot (QD) heterostructure improves the optoelectronic properties of the infrared photodetector as compared to the single SK or SML heterostructures. The discussed heterostructures for SK on SML are grown with three different spacer layer thicknesses (5, 7.5 and 10 nm) between SK and SML dots and each sample is grown with two different growth rates (0.1 ML/sec and 0.05 ML/sec). In this study, we are modulating the optical and structural properties of the heterogeneously coupled SK on SML structure with ex-situ annealing treatment. Rapid thermal annealing at 650 ℃ and 700 ℃ is done for all samples. Photoluminescence (PL) result shows blue shift in the peak position for annealed samples compared to the as-grown samples. The reason for this blue shift can be (1) In out-diffusion from the dots, or (2) Diminution in dot size. A reduction in full width half maxima (FWHM) of the PL spectra along with the annealing temperature is observed, which confirms the smaller size of dots after annealing. Additionally, substantial variation in strain profile for these hybrid structures has been discerned by high resolution X-ray diffraction (HRXRD). Hence, this study would definitely help to optimize the ex-situ annealing temperature on heterogeneously coupled SK-SML structure for wavelength tunable photodetection in the near infrared regime.

Here we report a novel approach to create tunable and reconfigurable microwave metamaterials using metal ink printing on a paper. Our approach enables easy-to-fabricate but still highly functional and tunable elements. An array of asymmetric split ring resonators was printed on a photopaper to induce Fano resonances in the microwave region (~ 10 GHz). Then, the printed paper was cut line by line and folded, so that a step height between neighboring unit cells can be created and tuned. With the varying step height between neighboring cells, our sample demonstrates significant spectral shifts and resonance tuning despite its simple geometry. Depending on the cutting direction, we observe either spectral redshift or blueshift. We explain our experimental observations based on the interactions between electric/magnetic dipoles in the neighboring unit cell. Moreover, we observe phase singularity at the zero amplitude position of the Fano resonance spectrum. The spectral phase exhibits a drastic change at this singularity point, and the phase spectrum can be also largely tuned with the geometry change in our sample. The drastic changes in phase could be very useful for various applications, such as optical sensing and beam steering.

Forster Resonance Energy Transfer (FRET) is a major interparticle energy transfer mechanism used in a wide range of modern-day applications. Hence, enhancing the FRET rate by different mechanisms has been extensively studied in the literature. Obtaining Plasmonic enhanced FRET by placing a metal nanoparticle (MNP) in the vicinity of energy exchanging molecules is one such mechanism. Here we present a model to elucidate the effects of extraneous surface charges present on such a vicinal MNP on the FRET rate considering the nonlocal response of the MNP. This model is based on the well established extended Mie theory of Bohren and Hunt along with the idea of introducing an effective dielectric function for the charged MNP. Our results indicate that the excess surface charges will lead to a blueshift in the resonance frequency and greater enhancements in the FRET rate for both local and nonlocal response based methods. Furthermore, we propose potential substitutes for noble metals that are conventionally used in plasmonic enhanced FRET.

This study examines the photoluminescence (PL) properties and strain distribution in InAs/InGaAs heterostructure for varying number of sub-monolayer (SML) quantum dot stacks (nSML). High resolution x-ray diffraction (HRXRD) probes the strain effects, whereas PL spectroscopy evaluated the optical response. The ground-state transition energies calculated from PL experiments were found to be 1.19, 1.13, 1.11, 1.12 eV for 4, 6, 8 and 10 stacks respectively. It was observed that, with the increasing nSML, the PL peak emission energy has an initial blue shift and later a red shift, due to build-up of strain energy propagating from the bottom layers of InAs quantum dots (QDs). The activation energies (Ea) calculated from temperature-dependent PL (TDPL) measurements are 414, 279, 260 and 231 meV for 4, 6, 8 and 10 stacks respectively. The Raman characterization results explores on the strain relaxation effects by observing the shift and broadening in TO and LO phonon peaks of GaAs bulk material. The strain energy distribution along the growth direction (z-direction) was studied using nextnano++ simulations. The relative change in hydrostatic and biaxial strain at a particular z - position was calculated to be 3.2% and 5.5% respectively These strain components are of prime importance in understanding the position of conduction and valence band energy levels and finally the band gap energy. Thus, with these articulated results, we conclude that sample with 6 SML stacks is the optimum choice for fabricating optoelectronic devices operating in long range infrared telecommunication regime.

Self-assembled III-V compound semiconductor quantum dots (QDs) on silicon (Si) substrate is much explored topic for optoelectronic devices. Here, we have investigated the optical and structural behavior of InAs QDs grown on (001)- oriented Si substrate. The heterostructure has been grown without Si-Ge buffer/graded layer and without Migration Enhanced Epitaxy layer which might reduce the anti-phase domain and dislocation propagation towards the active region. The heterostructure grown on Si (sample A) consists of a thick GaAs buffer layer which was followed by AlAs/GaAs super-lattice buffer layer and three consecutive layers of 2.7 ML InAs QDs with 50 nm GaAs capping. A heterostructure with similar active layers was grown on GaAs substrate (sample B). Samples were characterized using photoluminescence (PL) and high resolution X-ray diffraction (HRXRD) measurements. Sample A exhibited blue shifted PL peak as compared to sample B, which might be due to the formation of smaller dots. Moreover, from the power-dependent PL analysis, a multimodal and bimodal dot size distribution was observed in sample A and B respectively. HRXRD measurements showed the poor crystalline quality in sample A as compared to sample B. However, PL of sample A exhibited a higher intensity in comparison to sample B. In addition, sample A provided higher activation energy of 290 meV, whereas it was 198 meV in case of sample B. This indicates better confinement of charge carriers, which might improve the device performance. The optoelectronic performances could be enhanced by further optimizing this growth strategy through optimizing the dot layer periodicity, capping material, and capping thickness.

GaSe1-xSx mixed crystals have recently drawn worldwide attention owing to their wide bandgap, which can be tuned by varying the ratio between Se and S. We have addressed the scarcity of comprehensive studies on its dynamic properties by investigating the photoluminescence (PL) and time-resolved photoluminescence (TRPL) of GaSe1-xSx (x = 0, 0.1, 0.2, 0.5) mixed crystals at different temperatures (14 – 300 K) using 404 nm excitation from a Ti:Sapphire laser. This paper aims to show that the PL spectra and the lifetime of GaSe1-xSx could be used to determine the stacking type and composition of the sample. Three Gaussian peaks were deconvoluted from the obtained PL spectrum and were attributed to excitons from the direct and indirect bandgaps. As the sulfur composition increases, the color of the emission changes and the PL spectra exhibits a blueshift. Selenium-rich samples, which have a e-stacking, have an orange emission while sulfur-rich samples, which have a e-β mixed stacking, have a yellow to green emission. TRPL results reveal that the lifetime becomes longer as the sulfur composition increases. The stacking type influences the separation and transfer of the carriers. Hence, sulfur-rich samples have a significantly longer lifetime than selenium-rich samples due to their β- stacking. As the temperature increases, the lifetime also becomes longer due to the increase of the non-radiative recombination rate, which plays a dominant role in the PL emission. These results are useful for the development of GaSe1-xSx-based optoelectronic devices in the red to the blue visible region.

Cesium based wide band gap inorganic perovskites evolve as a promising material for novel applications in optoelectronic devices due to high stability and band gap tunability. In this work, we have synthesized the inorganic CsPbCl3 nanoparticles (NPs) as well as Mn-doped CsPbCl3 NPs. Effect of Mn as dopant on the structural properties of CsPbCl3 has been investigated by performing the X-ray diffraction (XRD). XRD results clearly indicate lattice contraction due to the incorporation of Mn as a dopant. Photoluminescence (PL) plot of Mn-doped CsPbCl3 shows the emission of dual colour which is attributed to d to d band transition of Mn2+. Blue and Orange colour emission has been seen for CsPbCl3 and Mndoped CsPbCl3 NPs respectively. A theoretical study has been also performed within the framework of Density Functional Theory (DFT) to validate our experimental results. DFT calculated (experimentally calculated) lattice parameters for the optimized crystal structure of CsPbCl3 and Mn-doped CsPbCl3 are 5.608 A (5.621 A) and 5.563 A (5.574 A) respectively. These results also show a reduction in lattice parameters due to the introduction of Mn as a dopant in CsPbCl3 which are in good agreement with our XRD results. Electronic band structure calculation for Mn-doped CsPbCl3 shows the presence of additional energy levels around 2.06 eV in the band gap. Additionally, Blue shift phenomena have been found in the absorption coefficient plot due to the incorporation of Mn. This communication envisages the potential of these NPs in various optoelectronic devices including orange LEDs (Light-emitting diodes).

A Mach-Zehnder interferometer based on seven-core fiber (SCF) and muti-mode fiber (MMF) is proposed and experimentally demonstrated. The interferometer is fabricated by splicing a segment of SCF spliced with two MMFs. The SCF length and MMF length are 5cm and 1cm, respectively. When the broadband light is injected into the interferometer through a lead-in single mode fiber, a pronounced interference pattern appears in the transmission spectrum. By monitoring the wavelength and power shifts of interference dips, simultaneous measurement of strain and torsion can be achieved. The experimental results show that the wavelengths at interference dip have a blue shift with the increases of strain, but the wavelength does not respond to the torsion. The power sensitivities of the interference dip to the strain and torsion are sensitivities are 0.001dB /° and 0.16dB/°, respectively. The simultaneous measurement of strain and torsion is demonstrated based on the sensitive matrix. The proposed MZI exhibits the advantages of easy fabrication, low cost, and simultaneous measurement of strain and torsion, which will make a significant contribution to torsion measurement.

A spontaneous formation of SiGe is reported, which is induced at mesa sidewalls of Si-capped Ge epitaxial layers selectively grown on Si. Ultrahigh-vacuum chemical vapor deposition is used to grow Ge mesa stripes on (001) Si wafers partially covered with SiO2 masks, followed by a growth of Si capping layer. Micro-Raman spectra reveals that SiGe is formed selectively on the {113} sidewalls of Ge mesa structure running in the [110] direction, resulting from an intermixing between the Si capping and Ge layers, whereas no such SiGe is detected on the flat-top (001) mesa surface. An increased amount of SiGe is observed for stripe patterns misaligned from the [110] direction. This suggests that the atomic step/roughness on the sidewall contributes to the intermixing. The observed SiGe formation would be applied to the bandgap engineering to tune the operation wavelengths in Ge photonic devices on Si. In fact, a significant blue shift in the direct-gap light emission peak is observed for submicron-wide Ge mesa structures with no flat-top (001) surface, where the surface is totally surrounded by SiGe.

We fabricated a polydimethylsiloxane (PDMS)-coated silica microbubble cavity with rich whispering gallery modes (WGMs). An electromagnetically induced transparency (EIT) window is realized through experimentally coupling a tapered fiber with the PDMS-coated microbubble resonator (MBR). There is a high-Q mode in the vicinity of a low-Q mode in transmission spectra. The experimental results prove that the high-Q mode performs a small redshift while the low-Q mode performs a large blueshift when the input power increases. This attributes to the negative thermo-optical coefficient (TOC) of PDMS and the positive TOC of silica. An EIT-like window is realized when these two modes are on-resonance with same frequency.

In this paper, a thermally induced dielectric strain on quantum well intermixing (QWI) technique is employed on tensilestrained InGaP/InAlGaP laser structure, to promote inter-diffusion, in conjunction with cycle annealing at elevated temperature. A bandgap blueshift as large as large as ~250meV was observed for samples capped with a single and bilayer of the dielectric film (1μm-SiO2 and 0.1μm-Si3N4) and annealed at a high temperature (700-1000oC) for cycles of annealing steps. Samples subjected to this novel QWI technique for short duration and multiple cycle annealing steps shown a high degree of intermixing while maintaining strong photoluminescence (PL) intensity, narrow full wave at half maximum (FWHM) and good surface morphology. Laser devices fabricated using this technique, lased at a wavelength of 608nm with two facet power of ~46mW, indicating the high quality of the material. Our results show that thermal stress can be controlled by the engineering dielectric strain opening new perspectives for QWI of photonics devices.

GaN-based high-power laser diodes (LDs) have attracted tremendous interests in next-generation lighting applications, such as laser display, car laser light. However, high injection current usually brings inevitable drawbacks, including the well-known efficiency droop, Auger recombination and self-heating which obstruct further improvements of GaN-based optoelectrical devices. In this paper, influence of hole overflow at high injection current in an asymmetric GaN-based highpower blue LD has been comprehensively investigated and successfully suppressed by employing a new sandwiched GaN/AlGaN/GaN lower quantum barrier (GAG-LQB). Systematical simulations and measurements of structural and optical properties are carried out. As a result, the V-shaped defects induced by thick n-InGaN waveguide layer are apparently eliminated, which provides a more growth-friendly platform for deposition of the rest epitaxial layers and thus a better crystalline quality is obtained. On the other hand, the modified LD exhibits better photo-electrical properties with slope efficiency (SE) increasing from 0.98 to 1.24 and wall-plug efficiency (WPE) increasing from 18.7% to 20.5% at a high current of 1.5 A and no obvious efficiency droop is observed at a current as high as 2 A compared with the conventional one, because the middle-inserted AlGaN layer could form an extra barrier on the valence band to weaken the hole overflow and enhance the radiative recombination. Furthermore, the in-plane compressive strain induced by InGaN quantum wells (QWs) is also partially compensated by the tensile strain induced by the AlGaN layer. Therefore, the piezoelectric fieldinduced polarization is effectively alleviated and the wavelength blueshift is reduced from 7 nm to 1.6 nm.

A localized surface plasmon resonance (LSPR) temperature sensor based on photonic crystal fiber (PCF) filled with liquid and silver nanowires is demonstrated both theoretically and experimentally. Simulation results show that a blueshift is appeared along with temperature increasing. The resonance wavelength and resonance intensity can be tuned effectively by adjusting the volume ratios of the liquid constituents. To investigate the sensor’s performance, a large temperature range from 25°C to 60°C is detected in experiment and the sensitivity of -2.08 nm/°C with figure of merit (FOM) 0.1572 is obtained. The all-fiber device with strong mechanical stability is easy to realize remote sensing by changing the downlead fiber length, also promising for developing a high sensitive, real-time and distribute fiber sensor in temperature sensing applications.

In this paper, we present a numerically study of the nanoscale refractive index sensor based on periodically modulated graphene ribbon arrays with finite-difference time-domain method (FDTD). The results show that the resonance wavelengths of the graphene metamaterials structure have an approximate linear correlation with the refractive index of the dielectric substrate, which can be used as the refractive index sensor exhibits a higher sensitive of 3069.1 nm/RIU. Furthermore, the resonant wavelength of the structure tends to exhibit a clearly blue shift with the Fermi-level (Ef) of graphene ribbons increasing. And the shift of the resonant peak ups to 4906.3 nm per unit Fermi level. Besides, the influence of ribbon-width and Fermi level of the graphene on the performance of sensor are investigated in details. We believe that the work is useful for the design and application of the plasmonic refractive index sensors based on a grapheme ribbon array.

We report the wavelength tuning of type-II “W” quantum well of interband cascade laser. By changing the thickness of the InAs electron well, the wavelength of the active region is adjusted. We found that the whole 3-4 μm spectra can be realized and the intensity was basically the same by measuring the photoluminescence (PL) of the active region. It showed that the type-II “W” quantum well of interband cascade laser can achieve 3-4 μm range without attenuation. In addition, we calculated the wavelength of quantum well of different InAs thickness by the 8-band k·p method. And we found that the wavelength of the active region varies with the thickness of the InAs electron well, which is consistent with the theory. In addition, the measured wavelength was different from the theoretical wavelength, which may be due to the As incorporation. The incorporation of As into the InGaSb layer will lead to blue shift in the wavelength.

Plasmonic nanoprisms with and without truncation in the form of Au-dielectric- Au and Ag-dielectric- Ag sandwich structures have been simulated using finite-difference time-domain (FDTD) simulation technique. Effect of dielectric material thickness on dipole resonance were studied in detail. Truncation introduced a blue shift in dipole resonance for silver and gold sandwich. For ideal gold and silver sandwich, the dipole resonance was not significantly affected for smaller thickness of dielectric material. However, for truncated sandwiches of gold and silver exhibited a gradual red shift with increase in thickness of dielectric layer. To conclude, the thickness of dielectric layer employed in sandwich can be used as a tunable parameter towards exhibition of dipole resonance regardless of gold or silver.

GaN nanowire LEDs with radial p-i-n junctions were grown by molecular beam epitaxy using N-polar selective area growth on Si(111) substrates. The N-polar selective area growth process facilitated the growth of isolated and high-aspect-ratio n-type NW cores that were not subject to self-shadowing effects during the subsequent growth of a conformal low-temperature Mg:GaN shell. LED devices were fabricated from single-NW and multiple-NW arrays in their as-grown configuration by contacting the n-type core through an underlying conductive GaN layer and the p-type NW shell via a metallization layer. The NW LEDs exhibited rectifying I-V characteristics with a sharp turn-on voltage near the GaN bandgap and low reverse bias leakage current. Under forward bias, the NW LEDs produced electroluminescence with a peak emission wavelength near 380 nm and exhibited a small spectral blueshift with increasing current injection, both of which are consistent with electron recombination in the p-type shell layer through donor-acceptor-pair recombination. These core-shell NW devices demonstrate N-polar selective area growth as an effective technique for producing on-chip nanoscale light sources.

Three treatments (normal soil water condition, CK; continual submergence condition, T1; and submergence and drought alternation condition, T2) are adopted. The reflectance spectra of Pinuse lliottii Engelm leaves, the red edge parameters and the corresponding chlorophyll content are measured, and the relationship between the red edge parameters and total chlorophyll concentration are analyzed. The results show that: (1) There are “blue shift” phenomena before 24d and “red shift” after 24d for the position of λred (Red edge position). The opposite phenomenon occurs for Dλred (Red edge amplitude). The Sred (Red edge area) appear “blue shift” for the case T1 and T2. (2)There is extremely significant correlation between chlorophyll content and red edge position, and there is significant correlation between chlorophyll content and red edge area, but the correlation between chlorophyll content and red edge amplitude is poor. The correlation coefficient between chlorophyll content and red edge position is 0.762. (3)The red edge position, kurtosis and skewness, which are computed by spectral curve at range 680-760nm of Pinuse lliottii Engelmare considered the input variables for artificial neural networks. The correlation coefficient is 0.928, and it obviously improves the accuracy of the estimation of the total chlorophyll concentration.

We recently described a technique to monitor heparin anticoagulation therapy in real-time using methylene blue and photoacoustic imaging. The photoacoustic signal of methylene blue was significantly amplified in the presence of heparin, but the exact mechanism underlying this novel photoacoustic behavior remains unclear. Here, we showed that the signal amplification was due to the aggregation of methylene blue. Methylene blue formed different aggregates in water and phosphate buffered saline (PBS). In water, the absorbance maximum of methylene blue with heparin from 0 to 3 U/mL blue shifted from 660 to 570 nm and the corresponding fluorescence intensity decreased 6-fold, which indicated the methylene blue aggregated from monomer to dimer and eventually to high order aggregates. Furthermore, the corresponding 0.04 ppm chemical shift of the proton in the phenothiazine ring of methylene blue from the nuclear magnetic resonance spectrum suggested the electron delocalization and self-aggregation of methylene blue. The coupling of methylene blue molecules results in extra vibrational relaxations within the split exciton states, and this causes enhanced photoacoustic signal. In PBS, we observed the aggregation of methylene blue/heparin complex using transmission electron microscopy (size=150.5 nm), but the absorbance maximum reversed back to 660 nm. This suggested the methylene blue formed monomer bound to heparin—the heparin could not self-aggregate due to electrostatic repulsive forces. The methylene blue bound monomers experienced less degree of freedom than free monomers and therefore caused excess photoacoustic signal.

Atomically thin transition-metal dichalcogenide (TMD) semiconductors possess strong Coulomb interactions due to reduced dielectric screening, leading to the formation of excitons with exceptionally large binding energies. The enhanced stability of excitons in these materials provides a unique platform to investigate excitonic interactions at room temperature and to examine the role of plasma effects and excitonic interactions over a broad range of excitation densities. We report an excitation-density dependent crossover between two regimes: Using ultrafast absorption spectroscopy, we observe a pronounced red shift of the exciton resonance followed by an anomalous blue shift with increasing excitation density. Using both material-realistic computation and phenomenological modeling, we attribute this observation to long-range Coulomb interaction in the presence of plasma screening in an attraction-repulsion crossover with the short-ranged exciton-exciton interaction that mimics the Lennard-Jones potential between atoms, suggesting a strong analogy between excitons and atoms in respect of inter-particle interaction. Our findings underline the important role of many-particle renormalizations and screening due to excited carriers in the device-relevant regime of optically or electrically excited TMDs.

ZnO has potential application in the field of short wavelength devices like LED’s, laser diodes, UV detectors etc, because of its wide band gap (3.34 eV) and high exciton binding energy (60 meV). ZnO possess N-type conductivity due to presence of defects arising from oxygen and zinc interstitial vacancies. In order to achieve P-type or intrinsic carrier concentration an implantation study is preferred. In this report, we have varied phosphorous implantation time and studied its effect on optical as well structural properties of RF sputtered ZnO thin-films. Implantation was carried out using Plasma Immersion ion implantation technique for 10 and 20 s. These films were further annealed at 900°C for 10 s in oxygen ambient to activate phosphorous dopants. Low temperature photoluminescence (PL) spectra measured two distinct peaks at 3.32 and 3.199 eV for 20 s implanted sample annealed at 900°C. Temperature dependent PL measurement shows slightly blue shift in peak position from 18 K to 300 K. 3.199 eV peak can be attributed to donoracceptor pair (DAP) emission and 3.32 eV peak corresponds to conduction-band-to-acceptor (eA0) transition. High resolution x-ray diffraction revels dominant (002) peak from all samples. Increasing implantation time resulted in low peak intensity suggesting a formation of implantation related defects. Compression in C-axis with implantation time indicates incorporation of phosphorus in the formed film. Improvement in surface quality was observed from 20 s implanted sample which annealed at 900°C.

The hydrostatic (ehy) and biaxial (ebi) strain in lateral (x) and growth (z) direction have been computed and compared for InAs quantum dot (QD) with different capping. The capping layers are: GaAs, InGaAs/GaAs, InAlGaAs/GaAs, InGaAs/InAlGaAs/GaAs, InAlGaAs/InGaAs/GaAs, and the total thickness is kept constant for all QD structures. The strain distribution is mainly confined within the dot and dies down towards the capping layer. The movement of conduction band edges is controlled by hydrostatic strain. QDs capped with InAlGaAs/InGaAs/GaAs and InAlGaAs/GaAs shows lower magnitude of ehy, which indicates better carrier confinement as compared to other capping. The electrostatic potential obtained for the InAlGaAs capped QDs is larger (~0.5 V) than other structures. The valence band splitting into the heavy hole and light hole depends on the biaxial strain. It is observed that GaAs and InAlGaAs/InGaAs/GaAs capping has the smallest and largest values of ebi respectively in the growth direction. The GaAs capped QD structure has a smaller ebi, which would increase the energy of the ground state hole, leading to blue shift in photoluminescence spectrum. However, the ground hole state has a lower energy due to larger ebi in InAlGaAs/InGaAs/GaAs capped QD, which results in a red shift in the photoluminescence spectrum (~1.35 μm at 300 K). Nonetheless, InAlGaAs capped QDs shows better results in the lateral direction also. Thus, based on the strain profile, QDs capped with InAlGaAs as the first capping layer is the optimized structure which can be useful for various optoelectronic applications.

In this letter, Raman spectroscopy was used to study the variation of transfer graphene. First, the Raman spectroscopy of chemical vapor deposition (CVD)-grown monolayer graphene was compared with that of mechanical exfoliated graphene, the 2D Raman band frequency of monolayer graphene grown on copper foils by CVD showed a blue shift upto 12 cm -1 . Then, the CVD-grown graphene on copper substrates was transferred to SiO 2 (300nm)/Si by wet transfer method, that caused a 2D-band redshift by 15cm -1 compared with the graphene before transferred, besides, the defects appeared in some regions. According to the changes of Raman spectrum, the strain was confirmed as the most important reason in the letter. The observation of the Raman shifts helps us to gain more physical insights into the transfer of graphene.

With rapid advancement of infrared detecting technology in both military and civil domains, the photo-electronic performances of near-infrared detectors have been widely concerned. Currently, near-infrared detectors demonstrate some problems such as low sensitivity, low detectivity, and relatively small array scale. The current studies show that surface plasmons (SPs) stimulated over the surface of metallic nanostructures by incident light can be used to break the diffraction limit and thus concentrate light into sub-wavelength scale, so as to indicate a method to develop a new type of infrared absorber or detector with very large array. In this paper, we present the design and characterization of periodically patterned metallic nanostructures that combine nanometer thickness aluminum film with silicon wafer. Numerical computations show that there are some valleys caused by surface plasmons in the reflection spectrum in the infrared region, and both red shift and blue shift of the reflection spectrum were observed through changing the nanostructural parameters such as angle α and diameters D. Moreover, the strong E-field intensity is located at the sharp corner of the nano-structures.

In0.227GaAs/GaAsN0.011 was introduced as a 1.2-eV multiple quantum well (MQW) with a flat conduction band (FCB) in which a conduction band edge of GaAsN was adjusted to be equal to that of InGaAs. This MQW was established as a candidate material for a middle absorption layer of three-junction solar cell since electron confinement was eliminated and a short electron lifetime in GaNAs was compensated by InGaAs layer. The band alignment of MQW was characterized by the power-dependent photoluminescence (PL) measurement under low temperature. According to the band-anti crossing model, the FCB is possibly constructed since a small amount of incorporated N can drastically reduce the energy of the conduction band edge of GaAsN. The PL results demonstrated that In0.227GaAs/GaAsN MQW was a type-I structure when N content was below 1.1%, and became a type-II structure when N content was above 1.1%. The type-II MQW was characterized by the observation of blueshift of PL peak when increasing excitation power. This blueshift is a result of band-bending effect due to the accumulation of excited carriers at the interface between two materials, which is unique for the type-II MQW. In addition, it was observed that the activation energy estimated from the Arrhenius plot provided a minimum value in the structure with 1.1%N; the lowest activation energy indicated the weakest confinement energy of carriers in the structure. These results approved that a transition from type-I to type-II occurred when N content surpassed 1.1%, and our designed In0.227GaAs/GaAsN0.011 MQW was potentially the FCB structure.

Strong coupling between excitons and photons inside a microcavity leads to the formation of cavity polaritons, hybrid light-matter particles. Under suitable conditions, polaritons can emit coherent light without population inversion, whereby polariton lasing can exhibit a threshold at least an order of magnitude less than that of conventional photon lasing in the same material. Polaritons in organic semiconductors are stable at room temperature, due to their large exciton binding energy. This renders organic materials interesting for light-mater interaction experiments at ambient conditions. In this paper, we report on polariton-lasing using fluorescent proteins embedded in a planar microcavity. The typical laser-like threshold-behavior, manifesting in an intensity nonlinearity, coherence build-up with a linewidth drop and an interactioninduced blueshift stemming from the part-matter nature of polaritons are presented. Additionally, we show the possibility to confine photonic modes inside deterministically created traps by presenting discretized mode spectra.

A high sensitivity strain sensor based on cascaded cladding mode resonant double-clad fiber (DCF) and simple mode fiber is proposed. The basic principle of the sensor is analyzed, and the preparation of the sensor is performed. In different length of double-clad fiber, the strain sensing characteristics are analyzed detailedly. Experimental results show that, as the length of the connected double-clad fiber increases, the trough of the resonant spectrum will gradually increase. That is, the length of the access DCF is inversely proportional to the free spectral range. With the increase of tensile force, the resonance spectrum is blue shift, and the tension sensitivity can be up to -1.87nm/me.

Organic-inorganic perovskites have revolutionized the optoelectronics field, providing materials with a wide range of properties for solving numerous applications. Indeed, much recent work has been focused on nanostructured perovskites, with quantum dots, nanowires, and nanoplatelets showing tremendous potential. Here, we utilize the unique tunability of 2D perovskite nanoplatelets to build LEDs that span the visible spectrum. Quantum confinement in the z direction drives a significant blueshift, allowing for blue devices utilizing the bromide system and orange devices utilizing the iodide system. We demonstrate that excess ligand addition is crucial to achieving this blueshift in thin films that otherwise suffer from energy funneling. We build devices that show electroluminescence from 440 nm to 650 nm, although they still suffer from low efficiencies due to low photoluminescence quantum yields. We finally demonstrate that these materials suffer from reversible degradation with an applied electric field, further limiting the efficiency. The favorable optoelectronic properties of perovskite materials, combined with the blueshift due to quantum confinement, shows the promise of these materials as a new class of low cost emitters.

There has been great progress in recent years in advancing the state-of-the-art of Ga-free InAs/InAsSb superlattice (SL) materials for infrared detector applications, spurred by the observation of long minority carrier lifetimes in this material system. However, compositional and dimensional changes through antimony (Sb) segregation alter the detector properties from those originally designed. For this reason, in this work, the authors explore epitaxial conditions that can mitigate this segregation in order to produce high-quality SL materials for optimum detector performance. A nominal SL structure of 7.7 nm InAs/3.5 nm InAs0.7 Sb0.3 tailored for an approximately six-micron response at 5 K was used to optimize the epitaxial parameters. Since the growth of mixed AsSb alloys is complicated by the potential reaction of As with Sb surfaces, the authors vary the substrate temperature (Ts) in order to control the As surface reaction on a Sb surface. Experimental results indicate that the SL sample grown at the lowest investigated Ts produces the highest Sb-mole fraction x of ~0.3 in InAs1-x Sbx layers, which then decreases by 21 % as the Ts increases from 395 to 440 °C. This reduction causes an approximately 30 meV blueshift in the position of the excitonic photoluminescence (PL) peak. This finding differs from the results obtained from the Ga-containing InAs/GaSb SL equivalents, where the PL peak position remains constant at about 220 meV, regardless of Ts. The Ga-free SLs generally generate a broader PL linewidth than the corresponding Ga-containing SLs due to the higher spatial Sb distribution at the hetero-interfaces engendered by Sb segregation. In order for this newly proposed Ga-free SL materials to be viable for detector applications, the material problem associated with Sb segregation needs to be adequately controlled and further mitigated.

Low energy ion implantation induced quantum well intermixing is an attractive way to obtain bandgap tuning across laser heterostructures. This technique is well suited for InP based heterostructures where the amount of blueshift obtained is closely linked to the amount of point defects created through ion implantation. We have developed novel masking techniques for the fabrication of multiple bandgap heterostructures using a single ion implantation step through variable thickness masks. Two main approaches have been studied for ion implantation masking in order to address both high precision and large flexibility of the mask thickness.

There are two physical phenomena governing the light emission in InGaN quantum structures: the internal electric fields and the In composition fluctuations. Both these effects manifest through the blue shift of the wavelength emission with the excitation intensity and both of them have the pronounced influence on the light emitting properties of these structures. In order to discriminate between these two effects, we fabricated two identical structures: one with the quantum barriers doped with silicon (method for internal electric field screening) and the other with an undoped active region. Under the optical excitation the emission peak shifts by almost 35 nm (Si doped) and 50nm (without Si). Additionally, we studied temperature dependence of the emission peak position. In case of low temperatures and at RT and high pumping energy, emission energy position is almost the same for both samples. Our observations lead us to the conclusion that at low temperatures and at high pumping regime the Quantum Confined Stark Effect (QCSE) is totally suppressed. While this is understandable that at high carrier injection QCSE is screened, the origin of the low temperature effect is much less clear. We can speculate that at the lowest temperature the carriers are localized eliminating the spatial separation of holes and electrons wavefunctions. Measured cathodoluminescence (CL) maps show the same level of the indium fluctuations for both samples. At higher excitation the fluctuations starts to be less visible suggesting band filling of states. Finally we compare recombination times by means of time resolved photoluminescence.

Recently we have demonstrated a novel method of extending the cut-off wavelength of InAsSb nBn detectors, by incorporating a series of monolayers of InSb. Here we study photoluminescence and minority carrier lifetime of this InAsSb/InSb digital alloy. While increasing temperature from 15 K to 40 K we show a 14 meV blue shift of the photoluminescence peak energy and a decrease in lifetime. This deviation from the expected Varshni empirical relation indicates strong carrier localization. We contrast to photoluminescence and lifetime results in bulk InAsSb. We discuss implications of this localization for design of digital alloy InAsSb/InSb nBn detectors.

We present the electric field-induced tuning of the light transmission in a photonic crystal device. The device, with alternating layers of Silver and Titanium dioxide nanoparticles, shows a shift of around 10 nm for an applied voltage of 10 V. An accumulation of charges at the Silver/TiO2 interface due to electric field leads to an increase of the number of charges contributing to the plasma frequency in Silver. This results in a blue shift of the Silver plasmon band, with concomitant blue shift of the photonic band gap as a result of the decrease in the Silver dielectric function.

We report a single layer GaAsN/InAs/GaAsN quantum-dot-in-well (DWELL) structure with PL emission at 1.31μm important for applications in communication lasers. This extension has been achieved with a nitrogen composition of only 1.8% and QDs embedded within 1/6nm GaAsN which is higher compared to single layer QDs with GaAs and GaAsN capping layers as a result of confinement reduction on both sides of the QD energy levels. The structures remain as QDs till 800°C of annealing temperature alongwith a drastic enhancement in PL intensity as a result of annihilation of N-induced crystal defects which provide non-radiative recombination centers for carriers in the as-grown sample which is responsible for degraded luminescence. A typical highly asymmetric PL signature observed in dilute nitride structures is seen with a sharp cut-off at lower wavelengths and a large exponential tail at higher wavelengths in the as-grown and 650°C annealed samples. This is due to the presence of localized excitonic states extending into the bandgap close to the band edges. For higher annealing temperatures, this asymmetry disappears indicating an improvement in uniformity of nitrogen distribution and absence of localized states; which is also confirmed from a smaller blueshift in excitation intensity-dependent PL spectra of these samples. Well-resolved ground and first excited states in the PL spectrum of 700°C annealed sample indicates an improvement in QD confinement.

Epitaxially-grown 10-layer coupled InAs quantum dots with GaAsN/GaAs barrier layers have been investigated. The PL spectra was seen to be a complex convolution of bimodal distribution of QDs along with an asymmetric signature introduced by incorporation of nitrogen into the structures. Reducing the GaAsN/GaAs barrier thickness (from 2/16nm to 2/8nm) resulted in an improvement of PL linewidth as low as 20meV of the dominant PL peak for the sample with thinnest barrier layer. A blueshift in emission was observed due to higher indium intermixing as a result of an increase in overall strain in the multilayer structure. The highly asymmetric exponential tail signature evident from the PL spectra of as-grown samples indicated a higher presence of localized N-induced excitonic states near the conduction band edge. Samples with thicker barriers showed relatively lower asymmetry compared to samples with thinner barriers. Also, samples with thinner barriers showed an arrest in blueshift in the PL spectra with annealing temperature indicating thermal stability.

The scientific background in the field of the laser induced damage processes in optical coatings has been significantly extended during the last decades. Especially for the ultra-short pulse regime a clear correlation between the electronic material parameters and the laser damage threshold could be demonstrated. In the present study, the quantization in nanolaminates is investigated to gain a deeper insight into the behavior of the blue shift of the bandgap in specific coating materials as well as to find approximations for the effective mass of the electrons. The theoretical predictions are correlated to the measurements. © 2016 SPIE. Downloading of the abstract is permitted for personal use only. Ministry for Science and Culture of Lower Saxony Volkswagen Stiftung

In this work, a 2D metallic nano-trench array was fabricated on gold metal surface by using an e-beam lithography patterning and etching process. Optical reflectance from the device was measured at oblique angles of incidence for TE and TM polarization. Near perfect light trapping was observed at different wavelengths for TE and TM polarization at oblique angle of incidence. As angle of incidence increases, light trapping wavelength has a red-shift for TM polarization and blue shift for TE polarization. The fabricated nano-trench device was also investigated for chemical sensor application. It was found that by varying the angle of incidence, the sensitivity changes with opposite trends for TE and TM polarization. Sensor sensitivity increases for TM polarization and decreases for TE polarization with increase of the oblique incident angle.

The enhanced nonlinear interaction in a silicon microcavity under coherent excitation is studied under different conditions. By controlling the pulse frequency drift, we guarantee, at every instant, the coincidence with the frequency resonance of the cavity that in the nonlinear regime suffers from a blue shift in time. This limiting shift effect is caused by the free carriers generated by the strong silicon two-photon absorption. Owing to the linear time-frequency relation of the pulse, the coupling efficiency to the drifted resonance can be maintained, further increasing the blue-shift. We study the input power effect after using different pulse durations.

A tension sensor of Photonic Crystal Fiber(PCF) is presented based on core-offset splicing and waist-enlarged fiber taper. The tension response characteristics of the sensor are studied experimentally. To analyzing the modal interference, many samples with different PCF lengths between the two splicing areas, different core-offset distances and different waist-enlarged fiber taper diameters are fabricated and tested. When the tension range is 0 to 4000μe, the results show that the spectrum is blue shift with the increasing of the axial tension. The sensitivity is-2.1 pm/μe. The experimental results show that the tension sensitivity can be not influenced by the PCF lengths, the core-offset distances.The waist-enlarged fiber taper diameters and the tension sensor is very sensitive to axial tension and the relationship between the wavelength shift and tension is linearity. To determine the number of the interfering modes, the transmission spectra of these sensor is transformed by the fast fourier transform (FFT) method. There are several peaks in the spatial frequency spectra at these sensors. Only one cladding mode is dominantly excited, while the other cladding modes are weak. The spatial frequency is proportional to the differential mode group index. Compared with the traditional fiber sensor, this sensor has some advantages including the easily fabricated, simple structure and high sensitivity. It can be used in industrial production, building monitoring, aerospace and other fields.