Infrared Photoluminescence Measurements Research Articles

Single grain infrared photoluminescence (IRPL) measurements of feldspars for dating

Existing infrared photoluminescence (IRPL) systems have used pulsed infrared stimulation (~830 nm) and measured IRPL emission (at 880 or 955 nm) using time resolved data collection with photomultipliers. Breakthrough of the infrared stimulation light overwhelms the IRPL, but the delayed emission during the laser-off period has been used instead.This paper describes a system for measurement of the IRPL signal from single sand-sized grains of feldspar. The attachment uses an electron-multiplying charge-coupled device (EMCCD) imaging system, and has two innovations that make it possible to use such a detector to obtain IRPL data. First, the optical detection system has been designed to minimise stray light and maximise the efficiency with which filters reject the stimulation light. This acts to reduce, but not eliminate, the breakthrough. Second, by placing the sample to be measured in a clearly defined sample grid, the spatial resolution provided by the EMCCD has been used to differentiate between regions of the image where IRPL is emitted and adjacent regions where only breakthrough is expected. This allows quantification of the breakthrough and effective subtraction to isolate the IRPL signal from the grains of interest.The attachment has been used to measure IRPL from single sand-sized grains of feldspar from an aeolian dune from New Zealand. A 1W UV LED (365 nm) is also added to the system and this is effective at resetting the IRPL signal, permitting a single aliquot regenerative dose (SAR) protocol to be used to measure equivalent dose (De). Measurement of a known laboratory dose (104 Gy) demonstrates the reproducibility of the attachment, with no overdispersion observed in the resulting single grain De values. The recovered dose is within 10% of the given dose. The natural IRPL signal yields De values from single grains with low overdispersion (22%) and giving a weighted mean value (103 ± 5.8 Gy) that is consistent with that obtained using post-IR IRSL measurements (105 ± 3.8 Gy). The attachment described here provides IRPL measurements on single grains suitable for exploring the potential of this novel and exciting signal for dating geological sediments.

Регистрация спектров инфракрасной фотолюминесценции методом стробируемого интегрирования в режиме активного вычитания фонового сигнала

A method based on the Fourier-transform infrared (FTIR) spectrometer has been implemented allowing infrared photoluminescence measurements with a low duty cycle of pump pulses. It reduces the uncontrolled heating of semiconductor structures by pump laser. The method was used to record the infrared photoluminescence spectra of test narrow-gap low dimensional heterostructures in the wavelength range of 1–5 μm. It was determined that for large reverse duty cycle (more then 20) the developed gated integration method has a better signal-to-noise ratio in the measured spectra compared to the traditionally used synchronous detection method (Lock-in amplification).

Photoinduced magnetization effect in ap-typeHg1−xMnxTesingle crystal investigated by infrared photoluminescence

Photoinduced magnetization (PIM) effect of ${\mathrm{Hg}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{Te}$ provides an attractive solution for realizing the quantum anomalous Hall effect in quantum wells with a light field. In this paper, the PIM effect of $p$-type ${\mathrm{Hg}}_{0.74}{\mathrm{Mn}}_{0.26}\mathrm{Te}$ single crystal was investigated by power-, polarization- and temperature-dependent photoluminescence (PL) measurements in both reflection and transmission geometries. Giant Zeeman splitting and polarization of PL spectra were observed without an external magnetic field evolving with excitation-power density of the pumping laser and temperature, which were accounted for by the PIM effect. The occurrence of the PIM was qualitatively understandable by the carrier-mediated mean-field theory known as the Zener model. The results indicate that infrared PL measurements with enhanced sensitivity and signal-to-noise ratio can serve as a convenient pathway for clarifying the PIM effect of semimagnetic semiconductors.

Raman and photoluminescence of Er 3+-doped SnO 2 obtained via the sol–gel technique from solutions with distinct pH

Raman and infrared photoluminescence measurements are carried out for Er 3+ -doped SnO 2 pellets (hard-pressed powders) obtained by the sol–gel technique from colloidal suspensions with distinct pH. Raman data indicate that bulk vibration modes are dominating for neutral pH. When the pH is modified, there is an intensity increase of acoustic surface modes. The evaluation of bulk and crystallite surface vibration modes indicates that the contribution of the bulk decreases for pH above the neutral and decreases even further for acid pH, becoming the surface vibration modes as dominating in this case. Infrared photoluminescence data indicate that the intensity of the emission generated from the 4I 13/2 → 4I 15/2 transition is strongly dependent on the pH of colloidal suspension, which may broaden the emission peaks due to overlapping of Stark levels.

Photosensitizer Methylene Blue-Semiconductor Nanocrystals Hybrid System for Photodynamic Therapy

In this work we report on the development of novel hybrid material with enhanced photodynamic properties based on methylene blue and CdTe nanocrystals. Absorption spectroscopy, visible photoluminescence spectroscopy and fluorescence lifetime imaging of this system reveal efficient charge transfer between nanocrystals and the methylene blue dye. Near infra-red photoluminescence measurements provide evidence for an increased efficiency of singlet oxygen production by the methylene blue dye. In vitro studies on the growth of HepG2 and HeLa cancerous cells were also performed, they point towards an improvement in the cell kill efficiency for the methylene blue-semiconductor nanocrystals hybrid system.

Optical properties of size quantized PbSe films chemically deposited on GaAs

PbSe films were chemically deposited with a range of controlled microstructures, from nanocrystalline to monocrystalline films. The crystal size in the nanocrystalline films was controlled in a range 7 to 25 nm with a fairly narrow size distribution, which allowed fine-tuning of the PbSe energy gap. The optical properties of the films were investigated using infrared (IR) transmission and IR photoluminescence measurements. The nanocrystalline PbSe films showed single bandgap values in the technologically important near-IR region. Two bandgap values, corresponding to both bulk and confined nanocrystals, were obtained for films with mixed microstructure. Strong blue shifts in both the absorption and emission peaks of the nanocrystalline layers were obtained. The bandgaps of the PbSe films were found to be in good agreement with theoretical calculations. The results point out the potential of these films for nanoscale optical device applications operating in the near-IR range.

Linear and nonlinear optical properties of erbium-implanted coherent array of submicron silica spheres

A coherent array of silica spheres, which was implanted with erbium ions, showed nonlinear behavior at λ=0.532 μm. This was attributed to a large nonlinear refraction effect, which was enhanced by the structure of the opaline matrix. In addition, near infrared photoluminescence measurements showed an overall enhancement as a function of the sphere’s size. A large photoluminescence peak was found around λ=900 nm and attributed to the lensing effect of the opaline matrix.

Low-voltage, high-speed AlSb/InAsSb HEMTs

Antimonide-based HEMTs have been fabricated with an InAsSb channel. Infra-red photoluminescence measurements at 5 K confirm that the addition of Sb changes the band structure from a staggered type II heterojunction lineup to a type I. These HEMTs with 0.1 /spl mu/m gate length exhibit decreased output conductance and improved voltage gain. At V/sub DS/=0.6 V, a microwave transconductance of 700 mS/mm and an output conductance of 110 mS/mm were obtained corresponding to a voltage gain of 6.

The growth of InP 1- xSb x by metalorganic chemical vapor deposition

InP 1- x Sb x was grown by metalorganic chemical vapor deposition under a variety of conditions. The V/III vapor phase ratio was varied from 327 to 12 over a temperature range of 450–525°C, at pressures of 77 to 660 Torr and growth rates of 0.30 to 2.0 μm/h. For some samples, the V/III vapor phase ratio was optimized for InP 1- x Sb x lattice matched to InAs to give smooth morphologies and lattice matching with a minimized variation of composition versus changes in the TMSb/(TMSb+PH 3) ratio. Examination by transmission electron microscopy indicates that the materials are not single phase, but have undergone a spinodal decomposition, which is consistent with thermodynamic calculations. When our specimen compositions are corrected for strain relaxation, the infrared photoluminescence measurements indicate a lower energy photoluminescence peak for these materials than had been previuosly reported in the literature. Infrared absorption and photoconductivity measurements indicate no sharp band edge as would be expected for a direct gap semiconductor. The observed broad spectra are consistent with alloy decomposition.

OMVPE growth and characterization of Bi-containing III–V alloys

For potential infrared detector applications, single crystalline InAsBi and InAsSbBi have been grown by atmospheric pressure OMVPE. Good quality epilayers with smooth surface morphologies were obtained by properly controlling the key growth parameter, the V/III ratio. The variation of lattice constant with solid composition for the InAs 1− x Bi x system, a = 6.058 + 0.966ß, provides evidence that Bi atoms incorporate substitutionally into the group V sublattice in the InAs zincblende structure. An extrapolated lattice parameter for the hypothetical zincblende InBi is 7.024Å. Thermodynamic calculations using the delta-lattice-parameter model predict that tremendously large miscibility gaps exist in the alloy system. Nevertheless, metastable InAsBi and InAsSbBi alloys were grown with concentrations far exceeding the solubility limit. For example 4.0 at% Bi was incorporated into InAs. Infrared photoluminescence measurements show a decrease of peak energy with increasing Bi concentration in the alloys, with d E g/d x=-55 meV/at% Bi. A study of the transmission spectra of these Bi-containing alloys confirms the above result.

Organometallic vapor-phase epitaxy growth and characterization of Bi-containing III/V alloys

For potential infrared detector applications, single-crystalline InAsBi and InAsSbBi have been grown by atmospheric pressure organometallic vapor-phase epitaxy. The precursors used were trimethylindium, trimethylantimony, trimethylbismuth, and arsine at growth temperatures of 375 and 400 °C. Good quality epilayers with smooth surface morphologies were obtained by properly controlling the key growth parameter, the V/III ratio. The variation of lattice constant with solid composition for the InAs1−xBix system, a=6.058+0.966x, provides evidence that Bi atoms indeed incorporate substitutionally into the As sites of the sublattice in the InAs zinc-blende structure. An extrapolated lattice parameter for the hypothetical zinc-blende InBi is 7.024 Å. Thermodynamic calculations of the InAs-InBi and InSb-InBi pseudobinary phase diagrams were carried out using the delta-lattice-parameter model using the lattice constant for zinc-blende InBi of 7.024 Å. The results agree well with experimental data. The calculations predict that the solid solubility limit of Bi in InAs is less than 0.025 at. %. The calculated maximum solubility limit is 2.1 at. % for Bi in InSb at the eutectic temperature of 132 °C. Thus, tremendously large miscibility gaps exist in both alloy systems. The critical temperature was predicted to be 2569 °C for the InAs-InBi system and 496 °C for the InSb-InBi system. The miscibility gap is the major factor limiting Bi incorporation into the InAsSb alloys. Nevertheless, metastable InAsBi and InAsSbBi alloys were grown with concentrations far exceeding the solubility limit. For example 3.1 at. % Bi was incorporated into InAs. Infrared photoluminescence measurements show a decrease of peak energy with increasing Bi concentration in the alloys, with dEg/dx=−55 meV/at. %Bi.

Demonstration of the effects of interface strain on band offsets in lattice-matched III-V semiconductor superlattices

A first principles total energy self-consistent pseudopotential calculation is used to predict the band offset in the lattice-matched superlattice InAs/Al0.8Ga0.2As0.14Sb0.86. We find that inclusion of interface strain changes the character of the band offset from nominally type II to strongly type II. The predicted band offset at the minimum energy configuration is in excellent agreement with the value determined from infrared photoluminescence measurements.

Photoluminescence and the band structure of InAsSb strained-layer superlattices

Infrared photoluminescence measurements were performed on InAs0.13Sb0.87 /InSb strained-layer superlattices. In thick layered structures we observed very low energy transitions proving that a type II superlattice occurs in the InAsSb system. Band structures were calculated based on estimates of the band offsets and strain shifts obtained from the photoluminescence data.

Photoluminescence of HgTe-CdTe superlattices: Comparison of theory and experiment

Infrared photoluminescence measurements have been made of a number of HgTe-CdTe superlattice samples as a function of temperature from liquid He to room temperature. The experimental results are compared with calculations of the band gap of these materials and the effects of layer thicknesses, valence-band offset, effective mass, and Hg in the CdTe layers are investigated. The data are in reasonable agreement with the calculations for zero (or small) valence-band offset and no Hg in the CdTe layers.