We observe and study the anomalous Stokes shift of CuAlS2/CdS quantum dots. While all known I-III... more We observe and study the anomalous Stokes shift of CuAlS2/CdS quantum dots. While all known I-III-VI2 semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS2/CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS2/CdS quantum dots are thus associated with cross sections less than 10-17 cm2 under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS2 and CdS layers. Besides their strong Stokes shift, CuAlS2/CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS2/CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm2.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
ABSTRACT We report on the photoemission properties of 500nm thick CsI films photocathodes. The su... more ABSTRACT We report on the photoemission properties of 500nm thick CsI films photocathodes. The surface morphology and electron diffraction pattern of 500nm thick “as-deposited” CsI and further “aged” CsI by exposing it to the humid air were investigated by means of transmission electron microscopy. It is observed that photoemission properties are degraded after long term exposure in humid air however there is no change in the film polycrystalline structure. After a 24h exposure to humid air, the average grain size of CsI films is increased by a factor of three.
Ashok Kumar*, R. K. Jain, R.N. Chakraborty , Triloki Pandit and B.K. Singh Deptartment of Physics... more Ashok Kumar*, R. K. Jain, R.N. Chakraborty , Triloki Pandit and B.K. Singh Deptartment of Physics, JRE Group of Institutions, Greater Noida-201308 INDIA Deptartment of Physics, ABES-IT Group of Institutions, NH-24 Ghaziabad -201009, INDIA Deptartment of Physics D S College Aligarh 202001, INDIA High Energy Physics lab, Physics Department Banaras Hindu University Varanasi 221005, INDIA . * email: ashokblp@gmail.com
We report the dielectric, ferroelectric, magnetic and magnetoelectric properties of three-phase c... more We report the dielectric, ferroelectric, magnetic and magnetoelectric properties of three-phase composite thick films (thickness~0.25 mm) of BaFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as BaFBT60) and SrFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as SrFBT60). A very strong magnetoelectric voltage coefficient (α33) of about 60 mV/cmOe and 40 mV/cmOe was observed at a small magnetic field of 300 Oe for the BaFBT60 and SrFBT60 films, respectively. The nature of the zero field cooling as well as the field cooling curves of composite films was suggested as a spin-glass type behavior. A remarkable value of magnetocapacitance (MC) of about 7.2% was observed for BaFBT60 composite film. The switchability phenomena of the ferroelectric domains were observed in the presence of the magnetic field of about 700 Oe. In addition, very significant information about the domain wall mobility was obtained from the irreversible (α) and reversible (ϵre) coefficients as calculated fr...
In the present work, the microcrystalline characteristics of KBr thin films have been investigate... more In the present work, the microcrystalline characteristics of KBr thin films have been investigated by evaluating the breadth of diffraction peak. The Wil-liamson–Hall, the Size-Strain plot and the single-line Voigt methods are employed to deconvolute the finite crystallite size and microstrain contribution from the broaden X-ray profile. The texture coefficient and dislocation density have been determined along each diffraction peak. Other relevant physical parameters such as stress, Young's modulus and energy density are also estimated using uniform stress deformation and uniform deformation energy density approximation of Williamson–Hall method.
Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum ef... more Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum efficiency (QE) measurement of 500 nm thick CsI film has been carried out in the wavelength range of 150 nm to 200 nm. Optical absorbance of 500 nm thick CsI film in the spectral range of 190 nm to 900 nm is analyzed and optical energy band gap is calculated using Tauc plot. To see the dispersive behavior of CsI film, refractive index has been determined by envelop plot of transmittance data, using Swanepoel method. Additional information on morphological and elemental composition results of CsI film, gained by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively are also reported in present work.
We observe and study the anomalous Stokes shift of CuAlS2/CdS quantum dots. While all known I-III... more We observe and study the anomalous Stokes shift of CuAlS2/CdS quantum dots. While all known I-III-VI2 semiconductor core/shell quantum dots show Stokes shifts in excess of 100 meV, the shift associated with CuAlS2/CdS quantum dots is uniquely large, even exceeding 1.4 eV in some cases. CuAlS2/CdS quantum dots are thus associated with cross sections less than 10-17 cm2 under the emission maximum. We investigate this anomaly using spectroscopic techniques and ascribe it to the existence of a strong type-II offset between CuAlS2 and CdS layers. Besides their strong Stokes shift, CuAlS2/CdS quantum dots also exhibit high quantum yields (63%) as well as long emission lifetimes (∼1500 ns). Because of the combined existence of these properties, CuAlS2/CdS quantum dots can act as tunable, transparent emitters over the entire visible spectrum. As a demonstration of their potential, we describe the construction of a wide area transparent lighting device with waveguided optical excitation and a clear aperture of 7.5 cm2.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2012
ABSTRACT We report on the photoemission properties of 500nm thick CsI films photocathodes. The su... more ABSTRACT We report on the photoemission properties of 500nm thick CsI films photocathodes. The surface morphology and electron diffraction pattern of 500nm thick “as-deposited” CsI and further “aged” CsI by exposing it to the humid air were investigated by means of transmission electron microscopy. It is observed that photoemission properties are degraded after long term exposure in humid air however there is no change in the film polycrystalline structure. After a 24h exposure to humid air, the average grain size of CsI films is increased by a factor of three.
Ashok Kumar*, R. K. Jain, R.N. Chakraborty , Triloki Pandit and B.K. Singh Deptartment of Physics... more Ashok Kumar*, R. K. Jain, R.N. Chakraborty , Triloki Pandit and B.K. Singh Deptartment of Physics, JRE Group of Institutions, Greater Noida-201308 INDIA Deptartment of Physics, ABES-IT Group of Institutions, NH-24 Ghaziabad -201009, INDIA Deptartment of Physics D S College Aligarh 202001, INDIA High Energy Physics lab, Physics Department Banaras Hindu University Varanasi 221005, INDIA . * email: ashokblp@gmail.com
We report the dielectric, ferroelectric, magnetic and magnetoelectric properties of three-phase c... more We report the dielectric, ferroelectric, magnetic and magnetoelectric properties of three-phase composite thick films (thickness~0.25 mm) of BaFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as BaFBT60) and SrFe12O19–poly(vinylidene-fluoride)–BaTiO3 (abbreviated as SrFBT60). A very strong magnetoelectric voltage coefficient (α33) of about 60 mV/cmOe and 40 mV/cmOe was observed at a small magnetic field of 300 Oe for the BaFBT60 and SrFBT60 films, respectively. The nature of the zero field cooling as well as the field cooling curves of composite films was suggested as a spin-glass type behavior. A remarkable value of magnetocapacitance (MC) of about 7.2% was observed for BaFBT60 composite film. The switchability phenomena of the ferroelectric domains were observed in the presence of the magnetic field of about 700 Oe. In addition, very significant information about the domain wall mobility was obtained from the irreversible (α) and reversible (ϵre) coefficients as calculated fr...
In the present work, the microcrystalline characteristics of KBr thin films have been investigate... more In the present work, the microcrystalline characteristics of KBr thin films have been investigated by evaluating the breadth of diffraction peak. The Wil-liamson–Hall, the Size-Strain plot and the single-line Voigt methods are employed to deconvolute the finite crystallite size and microstrain contribution from the broaden X-ray profile. The texture coefficient and dislocation density have been determined along each diffraction peak. Other relevant physical parameters such as stress, Young's modulus and energy density are also estimated using uniform stress deformation and uniform deformation energy density approximation of Williamson–Hall method.
Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum ef... more Performance of cesium iodide (CsI) as a reflective photocathode is presented. Absolute quantum efficiency (QE) measurement of 500 nm thick CsI film has been carried out in the wavelength range of 150 nm to 200 nm. Optical absorbance of 500 nm thick CsI film in the spectral range of 190 nm to 900 nm is analyzed and optical energy band gap is calculated using Tauc plot. To see the dispersive behavior of CsI film, refractive index has been determined by envelop plot of transmittance data, using Swanepoel method. Additional information on morphological and elemental composition results of CsI film, gained by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively are also reported in present work.
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