The luminescence properties of Dy3+ and Tb3+ single- as well as Dy3+ / Tb3+ double-doped barium borate glasses are investigated for their potential as light-converter. In double-doped barium borate glass an energy transfer from Dy3+ to Tb3+ is observed, i.e., an intense green luminescence from the doped Tb3+ ions results upon excitation at Dy3+-related absorption bands. Ray-tracing simulations allow for an evaluation of singleand double-doped light guides in different length. Here, the luminous flux and luminance values at the rough output face of a luminescent light guide are determined.
Lithium aluminoborate glass optically activated with the lanthanide ion dysprosium is investigated for its potential as luminescent light guide. For this, ray-tracing simulations are performed on the basis of transmission, photoluminescence, and quantum efficiency measurements. The luminous flux at the end of the light guide depends significantly on its length as well as on the roughness of the output face. The best results are obtained for a light guide length of approximately 70-80 mm with the side faces of the light guide coated with a 100 % reflecting mirror and a rough output face with Lambertian scattering characteristic. The input face is coated with a half-transmitting mirror which is transmissive for the excitation wavelength of 388 nm but reflective for the emission bands in the visible spectral range. For this light guide, a luminance of approximately 20 cd/mm2 is achieved for an excitation power density of 1W/mm2. The geometry of the light guide (cuboid / cylinder) has only a slight effect on the maximum luminance value.
A method to analyze the heat generation in luminescent barium borate glasses under continuous optical excitation is presented. The heat development is monitored by infrared thermography. Experimental surface temperature data are used as input for the differential heat equation to evaluate the volumetric heat rate from the spatial and temporal development of the temperature distribution. Having determined the volumetric heat rate in the glass, the heat generation under optical excitation can be estimated without further knowledge of optical parameters. Experiments on barium borate glasses with different doping levels are performed. For comparison, the heat generation is also estimated on the basis of optical parameters only to confirm the accuracy and validity of the presented method via infrared thermography. The experimentally determined total heat generation is in good agreement with those calculated from optical properties.
Rare-earth ions embedded in glassy matrices are promising materials for photon upconversion processes, e.g. to convert near infrared light to frequencies above the band gap of a solar cell to make it available for electrical power generation. One strategy to optimize the efficiency of such upconversion processes is to embed the active ions in a host matrix with minimal losses to non-radiative relaxation. For the model system of trivalent neodymium in fluorochlorozirconate (FCZ) glass it has been shown recently that a uniform growth of BaCl2 nanocrystals inside such glasses can decrease the probability of multi-phonon relaxation (MPR) drastically, leading to a huge increase in upconversion intensity for monochromatic illumination. To identify the key processes which may enhance or diminish the total upconversion efficiency, a comprehensive description for the optical dynamics of neodymium in FCZ glass ceramics has been developed on the basis of a rate equation system, including ion-photon, ion-phonon, and ion-ion interactions. An effective medium approach is utilized to account for the neodymium located in BaCl2 nanocrystals or the FCZ glass bulk, respectively. The numerous parameters required to enable for a reliable numerical simulation of the processes are obtained from theoretical approaches like Judd-Ofelt theory, as well as from experimental studies of luminescence decay after femtosecond excitation at various wavelengths and luminescence spectra under cw illumination at 800 nm wavelength. This rate equation model enables for a convenient, self-consistent description of all time-resolved and cw experiments on samples with different neodymium concentration. On this basis, the power dependence of upconversion spectra can be simulated in good agreement with the experimental result for 800 nm cw illumination. The model therefore forms an excellent tool for optimizing the upconversion efficiency of rare-earth doped luminescent material also under realistic (broadband illumination) conditions.
Rare-earth doped borate glasses are investigated for their potential as photon down-shifting cover glass for CdTe solar cells. Note, that CdTe solar cells have a poor response in the ultraviolet and blue spectral range due to absorption in the CdS buffer layer having a band gap of 2.4 eV. The following trivalent rare-earth ions are analyzed in detail: Sm3+, Eu3+, and Tb3+. These ions provide strong absorption bands in the ultraviolet / blue spectral range and an intense emission in the red (Sm3+ and Eu3+) or green (Tb3+) spectral range. The gain in short-circuit current density of a CdTe solar cell is calculated for different rare-earth ion concentrations. The calculations are based on the rare-earth’s absorption coefficients as well as their photoluminescence (PL) quantum efficiency. For Sm3+, the PL quantum efficiency depends significantly on the doping concentration. Finally, the potential of double-doped borate glasses, i.e. glasses doped with two different rare-earth ions, is investigated.
Two different transparent conductive oxides (TCO) were deposited by magnetron sputtering on borate glasses. The influence
of sputtering conditions on optical, electrical and microstructural properties was much higher for indium tin
oxide (ITO) than for aluminium-doped zinc oxide (AZO) films. Specific resistivity values obtained from simulation of
the optical spectra are in good agreement with values obtained from four-point probe measurements.
Neodymium-doped barium borate glasses are investigated for their potential as fluorescent concentrators for the near
infrared spectral range. Additional doping of the glasses with silver oxide and subsequent heat treatment leads to a reduction
of the doped silver ions and to the formation of metallic silver nanoparticles. The formation of the silver nanoparticles
is indicated by a broad surface plasmon-related extinction band at approximately 410 nm. The influence of the
silver nanoparticles on the fluorescence properties is investigated.
Sm3+-doped barium borate glasses are investigated for their potential as a superstrate for CdTe solar cells. The influence
of the Sm3+ conversion efficiency and the Sm2O3 doping level on the short circuit current density of a CdTe solar cell is
analyzed. CdTe solar cells with CdS layer thicknesses of 45 and 300 nm are evaluated. A 3.2 mm thick, 2 mol% Sm2O3-
doped glass superstrate enables a relative increase in the short circuit current density of approximately 1.4% and 2.9%
for a 45 and 300 nm CdS buffer layer, respectively, assuming 100% Sm3+ conversion efficiency.
In recent investigations using various analysis methods it has been shown that mechanical or thermal loading of PV
modules leads to mechanical stress in the module parts and especially in the encapsulated solar cells. Cracks in
crystalline solar cells are a characteristic defect that is caused by mechanical stress. They can lead to efficiency losses
and lifetime reduction of the modules.
This paper presents two experiments for systematic investigation of crack initiation and crack growth under thermal and
mechanical loading using electroluminescence. For this purpose PV modules and laminated test specimens on smaller
scales were produced including different cell types and module layouts. They were exposed to thermal cycling and to
mechanical loading derived from the international standard IEC 61215.
Cracks were observed mainly at the beginning and the end of the busbars and along the busbars. The cracks were
analyzed and evaluated statistically. The experimental results are compared to results from numerical simulations to
understand the reasons for the crack initiation and the observed crack growth and to allow module design optimization to
reduce the mechanical stress.
Periodic silicon nanostructures can be used for different kinds of gas sensors depending on the analyte concentration.
First we present an optical gas sensor based on the classical non-dispersive infrared technique for ppm-concentration
using ultra-compact photonic crystal gas cells. It is conceptually based on low group velocities inside a photonic crystal
gas cell and anti-reflection layers coupling light into the device. Experimentally, an enhancement of the CO2 infrared
absorption by a factor of 2.6 to 3.5 as compared to an empty cell, due to slow light inside a 2D silicon photonic crystal
gas cell, was observed; this is in excellent agreement with numerical simulations. In addition we report on silicon nanotip
arrays, suitable for gas ionization in ion mobility microspectrometers (micro-IMS) having detection ranges in principle
down to the ppt-range. Such instruments allow the detection of explosives, chemical warfare agents, and illicit drugs, e.g., at airports. We describe the fabrication process of large-scale-ordered nanotips with different tip shapes. Both silicon microstructures have been fabricated by photoelectrochemical etching of silicon.
Transparent, rare-earth doped fluorozirconate-based glasses and glass ceramics are attractive systems as up- and downconverters
to increase solar cell efficiency. For down-conversion applications, the efficiency of a silicon solar cell could
be significantly increased in the ultraviolet spectral range by placing a europium-doped glass ceramic on top. High
transparency is a key issue here to avoid scattering losses and to obtain high light output. Transmission spectra of fluorozirconate
glasses, which were additionally doped with chlorine ions to initiate the growth of BaCl2 nanoparticles
therein upon thermal annealing, show that the absorbance in the visible spectral depends significantly on the annealing
conditions. For up-conversion applications, erbium-doped fluorozironate glasses have been investigated. 2-dimensional
intensity mapping of the up-converted fluorescence yielded information on the homogeneity of the glass sample and the
erbium distribution therein. Depth scan experiments showed that the position of the focus of the excitation laser beam
plays a crucial role since saturation of the 2-photon up-conversion occurs for high excitation power.
Photovoltaic modules (PV modules) are supposed to have a lifetime of more than 20 years under various environmental
conditions like temperature changes, mechanical loads, etc. Common outdoor exposure may influence efficiency and
lifetime which necessitates assessment of PV module performance and detection of output deficits. For this purpose
reliable and nondestructive testing methods are desirable.
Commercially available PV modules were tested by different analysis methods. The PV module's electrical properties
were investigated by thermography and electroluminescence measurements. The combination of these two techniques is
well-suited to detect many cell and module defects. A crystalline module showed significant cell breakage after
temperature cycle test. To observe the mechanisms of this specific defect type laminated test specimens on smaller scales
were produced and analyzed over production process and during temperature cycles derived from the international
standards IEC 61215 and IEC 61646. The defect study on small scales allows conclusions about the defect's influence on
larger PV modules. Further methods capable for mechanical characterization like Laser Doppler vibrometry, surface
geometry scan and digital image correlation are presented briefly. The combination of the methods mentioned above
allows a very precise assessment of the mechanical and electrical capability which is essential for reliability and lifetime
concepts.
Borate glasses and borate glass ceramics are good candidates as a matrix material for fluorescent ions like samarium.
The chosen network modifier influences the fluorescence efficiency of the incorporated rare earth ion. Sm3+-doped lithium,
sodium, barium and lead borate glasses were examined with respect to their fluorescence properties and potential
use as a down-converting top layer of a solar cell.
The efficiency of thin film solar cells can be improved with the addition of a photon down-conversion top layer. This
layer converts incident ultraviolet light of the solar spectrum to visible light, which transmits through the glass and is
efficiently absorbed by the active layer of the solar cell. The results of our investigations of thin dielectric films and
fluorozirconate glass, both doped with Tb3+ ions, are presented. Tb3+ has absorption bands between 250 and 380 nm; the
corresponding emission bands are in the spectral range between 400 and 630 nm. Thin SiO2 and Al2O3 films with 0.04 -
10.18 at.% Tb were prepared by co-sputtering. For both as-deposited film systems, the highest fluorescence intensity is
found for a Tb3+ doping level of approximately 1 at.%; the fluorescence intensity of Tb3+ in SiO2 is higher than that in
Al2O3. Thermal treatment leads to an enhancement of the fluorescence intensity by more than one order of magnitude
and the highest fluorescence intensity is found for 2 at.% Tb for annealed thin SiO2 films containing Tb3+. For
comparison, the absorption and emission properties of Tb3+-doped fluorozirconate glass are investigated for a doping
level of 0.3 at.% Tb.
Transparent glasses as up- or down-converters are attractive systems to increase the efficiency of solar cells. Er-doped
fluorozirconate (FZ) glasses show an intense up-conversion upon excitation at 1540 nm. Transmission spectra show that
the absorbance at 1540 nm grows linearly with the Er-doping level. In Eu-doped FZ glasses, which were additionally
doped with chlorine ions, the growth of BaCl2 nanocrystals can be observed upon thermal annealing. For high annealing
temperatures a phase change from hexagonal to orthorhombic phase BaCl2 can be seen. Upon excitation in the ultraviolet
(UV) spectral range these glass ceramics emit an intense blue emission. A combination of a silicon solar cell and an
Eu-doped FZ glass ceramic as a down-converting top layer shows an increase in the short circuit current in the UV
spectral range compared to a solar cell without a down-converting top layer.
A simple benchtop apparatus has been built, to measure the x-ray imaging properties of fluorozirconate-based glassceramic
x-ray storage phosphor materials. The MTF degradation due to stimulating light spreading in the plate is lower
in comparison to optically turbid screens resulting in higher image MTF. In addition, the degree of transparency, or the
amount of light scattering at the wavelength of the stimulating (laser) light is adjustable by means of the glass preparation
process. The amount of stimulating exposure required for plate readout is generally higher than in previous systems,
but well within the range of commercially available laser systems, for practical readout times. The effects of flare
or unwanted readout due to back-reflection from the imaging plate is also less than in previous systems.
A novel telecentric scanning system has been developed that is able to rapidly read out the latent image stored in the
translucent imaging plates. This system features a reflective primary scan mirror to achieve telecentricity, optical correction
for scan line bow, and the design should enable the construction of a relatively inexpensive scanner system for
the translucent x-ray storage plates.
A new and promising approach for the design and fabrication of novel optical devices is the functionalization
of individual pores in 2D photonic crystals (PhC). This can be done by infiltrating the pores with polymers or
dyes. We present a method to locally infiltrate individual pores. This new technique enables the fabrication
of a new class of devices, such as optical switches or multiplexers. For the infiltration of individual pores 2D
PhC templates made of macroporous silicon were used. Local addressing of the pores is carried out by using
focused ion beam technology. For the infiltration itself the wetting assisted templating process is applied. We
will present experimentally the infiltration of different polymers and different optical designs.
KEYWORDS: Glasses, External quantum efficiency, Luminescence, Solar cells, Upconversion, Photons, Near infrared, Silicon solar cells, Doping, Solar energy
Transparent erbium-doped fluorozirconate (FZ) glasses are attractive systems for upconversion-based solar cells. Upconverted
fluorescence intensity vs. excitation power dependence was investigated for a series of erbium-doped FZ
glasses. It was found that the ratio of the 2-photon upconverted emission in the near infrared at 980 nm to the 3-photon
upconverted emissions in the visible at 530, 550, and 660 nm decreases with increasing excitation power. The integrated
upconverted fluorescence intensity per excitation power shows "saturation" upon increasing the excitation power,
while the point of saturation shifts to lower excitation power with increasing erbium doping level. To demonstrate
the potential of these upconverters for photovoltaic applications, the external quantum efficiency (EQE) of a commercial
monocrystalline silicon solar cell with an Er-doped FZ glass on top of it was measured. For an excitation power of
1 mW at a wavelength of 1540 nm an EQE of 1.6% was found for a 9.1 mol% Er-doped FZ glass. The samples investigated
were not optically coupled to the solar cell and no optical coating was applied to the glass surface.
Thermal processing of as-made fluorozirconate glasses which were additionally doped with neodymium and chlorine
ions leads to enhanced up-conversion fluorescence intensities in these glass ceramics. The samples were annealed between
240°C and 290°C while the optimum value was found for the 270°C sample. We investigated the power dependence
of the infrared fluorescence, the 2-photon up-conversion, and the 3-photon up-conversion fluorescence intensities
as well as the corresponding radiative lifetimes. In analogy to the up-conversion intensity, the radiative lifetime of the
Nd3+ fluorescence at about 880 nm depends significantly on the annealing temperature: the longest lifetime was observed
for the 270°C sample.
We present measurements of the thermal emission properties of 2D and 3D silicon photonic crystals using either
localized integrated emission sources or resistively heating the entire photonic crystals with and without substrate.
The in-plane as well as out-of-plane emission properties were recorded and compared to numerical simulation.
We developed a class of (semi-) transparent glass-ceramic storage phosphors for digital mammography. The glass ceramics are based on europium-doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of barium chloride nanoparticles therein. The glass ceramic is able to convert ionizing radiation into stable electron-hole pairs, which can be read out afterwards with a scanning laser beam in a so-called "photostimulated luminescence" (PSL) process. A number of experiments were done to measure materials and engineering parameters relevant to a point scanning readout system, and to allow projection of the Detective Quantum Efficiency (DQE) for the proposed x-ray storage phosphor system. These included measurement of the required stimulating exposure (laser power density times pixel dwell time), and integrated PSL signal (or "gain", expressed as the number of detected electrons per absorbed x-ray). Measurements of optical light spreading of the stimulating laser light were also done, since this effect determines the MTF of the scanning system. Calculations of x-ray absorption vs. imaging plate composition and thickness, and x-ray beam spectrum, were also completed. Finally, the measured parameters were used to project DQE vs. spatial frequency for the proposed detector, and to compare with commercially available electronic mammography systems.
The sensitivity of an infrared gas sensor depends on the interaction length between radiation and gas, i.e. a reduction in
cell size generally results in a reduced sensitivity, too. However, low group velocity regions in the bandstructure of
photonic crystals should enable the realization of very compact gas sensors. Using photonic crystals based on
macroporous silicon experimental results with CO2 show an increase of the gas sensitivity in the photonic crystal
compared to an empty cell of same dimensions. For practical applications the results are compared with gas
measurements using conventional multireflection cells and hollow fiber setups.
Fluorescence techniques are known for their high sensitivity and are widely used as analytical tools and detection methods for product and process control, material sciences, environmental and biotechnical analysis, molecular genetics, cell biology, medical diagnostics, and drug screening.
For routine measurements by fluorescence techniques the existence of an improved quality assurance is one of the basic needs. According to DIN/ISO 17025 certified standards are used for fluorescence diagnostics having the drawback of giving relative values only.
Typical requirements onto fluorescence reference materials or standards deal with the verification of the instrument performance as well as the improvement of the data comparability.
Especially for biomedical applications fluorescence labels are used for the detection of proteins. In particular these labels consist of nano crystalline materials like CdS and CdSe. The field of Non-Cadmium containing materials is under investigation.
In order to evaluate whether glass based materials can be used as standards it is necessary to calculate absolute values like absorption/excitation cross sections or relative quantum yields. This can be done using different quantities of dopands in glass, glass ceramics or crystals.
The investigated materials are based on different types of glass, silicate, phosphate and boron glass, which play a dominant role for the absorption and emission mechanism. Additional to the so-called elementary fluorescence properties induced by raw earth elements the formation of defects lead to higher cross sections additionally.
The main investigations deal with wavelength accuracy and lifetime of doped glasses, glass ceramics and crystalline samples. Moreover intensity patterns, homogeneity aspects and photo stability will be discussed.
Scintillators are the backbone of high-energy radiation detection devices. Most scintillators are based on inorganic crystals that have applications in medical radiography, nuclear medicine, security inspection, dosimetry, and high-energy physics. In this paper, we present a new type of scintillator that is based on glass ceramics (composites of glasses and crystals). These scintillators are made from Eu2+-activated fluorozirconate glasses that are co-doped with Ba2+, La3+, Al3+, Na+, and Cl-. Subsequent heat treatment of the glasses forms BaCl2 nano-crystals (10-20 nm in size) that are embedded in the glass matrix. The resulting scintillators are transparent, efficient, inexpensive to fabricate, and easy to scale up. The physical structure and x-ray imaging performance of these glass-ceramic scintillators are presented, and an application of these materials to micro-computed tomography is demonstrated. Our study suggests that these glass-ceramic scintillators have high potential for medical x-ray imaging.
We investigated the energy-dependent scintillation intensity of Eu-doped fluorozirconate glass-ceramic x-ray detectors in the energy range from 6 to 20 keV. The experiments were performed at the Advanced Photon Source, Argonne National Laboratory. The glass ceramics are based on Eu-doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of BaCl2 nanocrystals therein. The x-ray excited scintillation is mainly due to the 5d-4f transition of Eu2+ embedded in the BaCl2 nanocrystals; Eu2+ in the glass does not luminesce. Upon appropriate annealing the nanocrystals grow and undergo a phase transition from a hexagonal to an orthorhombic phase of BaCl2. The scintillation intensity is investigated as a function of the x-ray energy as well as of the particle size and structure of the embedded nanoparticles. The scintillation intensity versus x-ray energy dependence shows that the intensity is inversely proportional to the photoelectric absorption of the material, i.e. the more photoelectric absorption the less scintillation.
We demonstrate how ultrashort optical pulses can be used to tune the optical properties of a photonic crystal using the real (Kerr) and imaginary (two photon absorption) parts of a third order optical nonlinearity. We demonstrate this effect by tuning the long (1.6 μm) and short wavelength (1.3 μm) band-edges of a stop-gap in a 2-D silicon photonic crystal. From pump-probe reflectivity experiments using 150-200 fs pulses, we observe that a 2 μm pulse induces optical tuning of the 1.3 μm edge via the Kerr effect whereas a 1.76 μm pulse induces tuning of the 1.6 μm band edge via both Kerr and Drude effects with the latter related to 2-photon induced generation of free carriers with a lifetime of ~ 700ps. In separate experiments we show how the properties of the pump eigenmode can influence the magnitude and temporal dynamics of the tuning behavior. When carriers are injected via a pump eigenmode for which the initial carrier distribution is inhomogeneous, diffusion is responsible for an initially fast (10 ps time scale) component of the recovery of the probe reflectivity with surface recombination accounting for a slower response (700 ps time scale) after the carriers are nearly uniformly distributed within the silicon backbone. When carriers are initially generated homogeneously, surface recombination alone controls the time evolution of the probed mode.
The real (Kerr) and imaginary (two photon absorption) parts of a
third order optical nonlinearity are used to tune the long (1.6μm) and short (1.3μm) wavelength band edges of a stop gap in a two-dimensional silicon photonic crystal. The reflectance of the probe beam reveals information about the rise and fall times of the switching. More detailed investigations show the different time response of reflectance for different optical modes excited by the pump beam. We present a model based on simple "pertubation" formalism that can explain how any mode of photonic crystals is affected by general, weak refractive index pertubations.
Highly-ordered two dimensional arrays of monodisperse silver and nickel nanowires were prepared in an alumina matrix. The nearly 100% filling of the template with metal was obtained by improved electrochemical deposition technique. The light propagation in the direction of the long axis of the metal nanowires were studied by far field spectroscopy and the results were compared with the generalized Mie theory. By selectively dissolving the matrix at a constant etching rate the we investigate the surface enhanced Raman scattering (SERS) and the results are interpreted with theoretical models. The enhanced SERS signal can be recorded until the whole matrix was removed and the ordering of the metal nanowires collapses.
The bandstructure of photonic crystals offers intriguing possibilities for the manipulation of electromagnetic waves. During the last years, research has mainly focussed on the application of these photonic crystal properties in the telecom area. We suggest utilization of photonic crystals for sensor applications such as qualitative and quantitative gas and liquid analysis. Taking advantage of the low group velocity and certain mode distributions for some ~k-points in the bandstructure of a photonic crystal should enable the realization of very compact sensor devices. We show different device configurations of a photonic crystal based on macroporous silicon that fulfill the demands to serve as a compact gas sensor.
X-ray storage phosphors have several advantages over traditional films as well as digital X-ray detectors based on thin-film transistors (TFT). Commercially used storage phosphors do not have high resolution due to light scattering from powder grains. To solve this problem, we have developed storage phosphor plates based on modified fluorozirconate (ZBLAN) glasses. The newly developed imaging plates are “grainless” and, therefore, can significantly reduce light scattering and improve image resolution. To study the structure and image performance of the novel storage phosphor plates, we conducted X-ray diffraction (XRD) and X-ray imaging analyses at the Advanced Photon Source, Argonne National Laboratory. The XRD results show that BaCl2 crystallites are embedded in the glass matrix. These crystallites enlarge and are under residual stress after heat treatment. The X-ray imaging study shows that these storage phosphor plates have a much better resolution than a commercially used storage phosphor screen. The results also show that some of the glass ceramics are high-resolution scintillators. Our study demonstrates that these fluorozirconate-based glass ceramics are a promising candidate for high-resolution digital X-ray detectors for both medical and scientific research purposes.
The bandstructure of photonic crystals offers intriguing
possibilities for the manipulation of electromagnetic waves.
During the last years, research has mainly focussed on the
application of these photonic crystal properties in the telecom
area. We suggest utilization of photonic crystals for sensor
applications such as qualitative and quantitative gas and liquid
analysis. Taking advantage of the low group velocity and certain
mode distributions for some k-points in the bandstructure
of a photonic crystal should enable the realization of very
compact sensor devices. We show different device configurations of
a photonic crystal based on macroporous silicon that fulfill the
demands to serve as a compact gas sensor.
We demonstrate three ways in which the optical band-gap of 2-D macroporous silicon photonic crystals can be tuned. In the first method the temperature dependence of the refractive index of an infiltrated nematic liquid crystal is used to tune the high frequency edge of the photonic band gap by up to 70 nm for H-polarized radiation as the temperature is increased from 35 to 59°C. In a second technique we have optically pumped the silicon backbone using 150 fs, 800 nm pulses, injecting high density electron hole pairs. Through the induced changes to the dielectric constant via the Drude contribution we have observed shifts upt to 30 nm of the high frequency edge of the E-polarized band-gap. Finally, we show that below-band-gap radiation at 2.0 and 1.7 μm can induce changes to the optical properties of silicon via the Kerr effect and tune the band edges of the 2-D macroporous silicon photonic crystal.
We present and characterize hexagonal point defects in a two dimensional photonic crystal based on macroporous silicon. These point defects are prepatterned periodically, forming a superstructure within the photonic crystal after electrochemical etching. Spatially resolved, optical investigations related to morphological properties, like defect concentration and pore radius, are compared to bandstructure calculations. The confined defect states are identified and their interaction is evaluated quantitatively.
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