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Ullrich B.,National Autonomous University of Mexico | Ullrich B.,Ullrich Photonics LLC | Xi H.,Bowling Green State University | Wang J.S.,Air Force Research Lab
Applied Physics Letters | Year: 2016

The exposure of colloidal 2 nm PbS quantum dots to growing continuous wave laser excitation at 532 nm increases the photoluminescence intensity with the square root of the optical stimulus. The results herein in conjunction with previous findings [B. Ullrich and H. Xi, Opt. Lett. 38, 4698 (2013)] advocate the square root trend to be the general limiting function for photo-carrier transport and emission of optically excited nano-sized materials. We further show that the excitation of one electron-hole pair per quantum dot defines the saturation threshold for photoluminescence intensity and dynamic band filling. © 2016 AIP Publishing LLC. Source


Ullrich B.,National Autonomous University of Mexico | Ullrich B.,Ullrich Photonics LLC | Xi H.,Bowling Green State University | Wang J.S.,Air Force Research Lab
Journal of Applied Physics | Year: 2014

Increase in continuous wave laser excitation (6 W/cm2 to 120 W/cm2) of colloidal PbS quantum dots in the strongly quantized regime (diameters 2.0 nm and 4.7 nm) deposited on semi-insulating GaAs and glass causes a clear blue shift (0.019 eV and 0.080 eV) of the emission spectra. Proof of the applicability of a dynamic three-dimensional band filling model is the significance of the presented results and demonstrates the effective electronic coupling in quantum dot arrays similar to superlattices. The work also reveals the influence of quantum dot sizes on photo-doping effects. © 2014 AIP Publishing LLC. Source


Ullrich B.,National Autonomous University of Mexico | Ullrich B.,Ullrich Photonics LLC | Singh A.K.,National Autonomous University of Mexico | Barik P.,National Autonomous University of Mexico | And 2 more authors.
Optics Letters | Year: 2015

The intrinsic photoluminescence Stokes shift, i.e., the energy difference between optical band gap and emission peak, of 350 μm thick semi-insulating GaAs wafers is found to be 4 meV at room temperature. The result is based on the determination of the optical bulk band gap from the transmission trend via modified Urbach rule whose result is confirmed with the transmission derivative method. The findings reveal the detailed balance of the optically evoked transitions and disclose the intrinsic link between Stokes shift and the Urbach tail slope parameter. © 2015 Optical Society of America. Source


Ullrich B.,Ullrich Photonics LLC | Ullrich B.,Air Force Research Lab | Brown G.J.,Air Force Research Lab
Review of Scientific Instruments | Year: 2012

Although known for more than twenty years, there is limited information in the literature regarding the experimental parameters of lock-in based phase sensitive emission detection in conjunction with Fourier spectrometers. For this technique - also known as double modulation spectroscopy - we present a guideline for parameter optimization by measuring the photoluminescence of InSb:Te at cryogenic temperatures. © 2012 American Institute of Physics. Source


Shahi P.K.,Banaras Hindu University | Singh A.K.,National Autonomous University of Mexico | Rai S.B.,Banaras Hindu University | Ullrich B.,National Autonomous University of Mexico | Ullrich B.,Ullrich Photonics LLC
Sensors and Actuators, A: Physical | Year: 2014

The Eu(DBM)3Phen complex has been synthesized and dispersed in poly(methyl methacrylate) and polyvinyl alcohol matrices in order to explore its versatile applicability. Excitation spectroscopy monitored at 611 nm show intense ultraviolet-blue spectra (∼250 to 450 nm) pointing to efficient energy transfer from the organic ligands to the central Eu3+ ion. The excellent photoluminescence properties, i.e.; broad-band excitation spectra, sharp and intense emission, and long lifetime open the door for appealing multi-applications such as temperature sensing, ultraviolet light detection, and laser applications. Photoluminescence based temperature sensing with a sensitivity of up to 1.75% per K is demonstrated for the temperature range of 50-318 K, and additionally, ultraviolet radiation detection is demonstrated, whilst impinging ultraviolet intensities as weak as 96 nW/cm2 can be detected. The work further reports several essential device characteristics, such as emission dependence on impinging excitation intensity, sensor stability, and photoluminescence response times. Finally, by increasing the optical excitation, amplification in spontaneous emission and decrease of full width at half maximum take place, pointing to stimulated emission. This feature, in conjunction with the stimulated emission cross-section of 3.24 × 10-20 cm2, which is comparable to the Nd-Glass laser, suggests the suitability of the investigated lanthanide-polymer merger for laser realizations. © 2014 Elsevier B.V. Source

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