Continuously increasing demand for biomedical diagnostics requires advanced imaging techniques. Time-gated imaging (TGI) of photoluminent bioprobes has a number of unique features, such as possibility to cut-off the excitation and autofluorescence and provide photoluminescence (PL) lifetime information in every pixel. However, as the other bioimaging techniques, TGI itself is not able to overcome the problem of high attenuation of light in the biological tissues. In recent years, imaging in the biological windows of optical transparency in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges is being actively developed, providing an opportunity for the excitation and detection of PL signal in deeper biological tissues with higher resolution. In order to combine both advantages of NIR-SWIR imaging and TGI, we have built a time-gated imaging system performing in NIR-SWIR (900-1700nm) spectral range. Synchronizing setup has been developed in order to control delay between pulsed excitation source and NIR-SWIR camera. Through manipulation of the delay between the PL excitation source and imaging camera, stack of time-resolved PL images is obtained, which can be processed by the unmixing software. In summary, the developed technique allows us to distinguish and map regions of different NIR-SWIR PL lifetimes. An application of this method for spatial discrimination of rareearth ion doped nanoparticles emitting in NIR-SWIR range has been demonstrated.
Comparing to other optical imaging techniques, hyperspectral imaging (HSI) possesses a unique feature, being capable of not only obtaining a spatial information about a specimen, but also providing a spectral information in every image pixel. Being employed in biomedical applications, similarly to other optical bioimaging techniques, HSI struggles with limited light penetration depth, caused by high absorption and scattering of light by biological tissues. Overcoming the limitations of imaging in visible spectral range, optical bioimaging in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges (~700 –1700 nm) has being actively advanced in recent years, as due to the strongly reduced tissue absorption and scattering, NIR-SWIR imaging systems can achieve deeper tissue imaging with higher resolution. With the aim to combine both the advantages of SWIR imaging and HSI, we have built a hyperspectral imaging system operating in NIR-SWIR spectral region (900 – 1700 nm). The constructed HSI system is based on a wavelengths scanning method, with a liquid crystal tunable filter (LCTF) as a dispersion element. The spectral unmixing software has been developed to map the regions of the specified spectral features. Finally, an application of the developed method towards spatial differentiation of rare-earth doped nanoparticles emitting in NIR-SWIR range has been demonstrated.
KEYWORDS: Indium gallium arsenide, Solar cells, Gallium arsenide, Solar energy, Photovoltaics, Molecular beam epitaxy, Quantum wells, Temperature metrology, Video, Current controlled current source
A study of the photovoltaic properties of the GaAs-based solar cells with InGaAs quantum wire had been conducted. The research included the investigation of the photovoltage rise and decay transients, spectral photovoltage dependences at different temperatures. The objects investigated were GaAs-based solar cells with InGaAs quantum wire (QWR) embedded into space-charge-region of p-i-n junction. Samples with different In content and size of InGaAs nanoobjects had been created using molecular beam epitaxy. Unlike the reference cell, the ones containing the InGaAs QWR had shown higher sensitivity in the energy range 1.2 - 1.38 eV. This is caused by the spatial separation of electron-hole (e-h) pairs excited in the QWR due to band-to-band transition. Under selective excitation of the e-h pairs only in the InGaAs quantum wire the photovoltage rise transient is slower compared to the e-h generation in GaAs. This effect is explained by charge carriers release from the InGaAs quantum well into delocalized states of the surrounding GaAs. It was determined that the InGaAs quantum wires increase the recombination rate of the non-equilibrium carriers in the temperature range 80 to 290 K, which means that the quantum wires are the additional recombination centers.
The luminescent properties of InGaAs/GaAs heterostructures with InGaAs nanoscale objects were investigated. Multilayer heterostructures were grown using molecular beam epitaxy technique. The shapes of the photoluminescence spectra were studied in the temperature range from 10 K to 290 K. The electronic spectrum of heterosystems as well as the energy of interband transitions for InGaAs nano-objects were calculated for different sizes and InGaAs component composition. It is shown that the shape of the photoluminescence spectra is determined by the Gaussian distribution of the energy of band-to-band optical transitions between the ground states of the conduction band and valence band of nanoscale objects. The physical reason for the observed energy dispertion is the variation of sizes, heterogeneity of component composition and strain relief in the ensemble of InGaAs nano-objects. Non-monotonous temperature dependence of the width of the photoluminescence spectra indicates the existence of temperature-dependent redistribution of photoexcited charge carriers between neighbouring nanoislands having different energy of the ground states.
Structures with one-dimensional quantum objects in intermediate band are promising for their application in solar cells and photodetectors. We present analysis of dark current-voltage characteristics, photo-voltage decay and photo-voltage spectra for this structures in comparison with reference GaAs based structures. It has been shown that InGaAs quantum wires make a significant influence on J-V dependences and photo-voltage spectra. InGaAs QWRS are additional recombination centers and transitions between them dominated over by Shockley-Read-Hall recombination at low bias. The InGaAs/GaAs sample shows a significantly higher photo-voltage in the spectral range of 1.25-1.37 eV, as compared to a reference GaAs p-n junction, due to intermediate band transitions in the quantum wires.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.