Ultraviolet Absorption of KI Diluted in KCl Cryst als

Mahr, H.

doi:10.1103/physrev.125.1510

Cited by 234 publications

(45 citation statements)

References 24 publications

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“…where α o and hν o are constants [26] dependent on the material and σ, known as the steepness parameter, is a temperature dependent parameter characterizing the broadening of the absorption edge due to electron-phonon or exciton-phonon interactions [27]. At a constant temperature, graph representing ln α on the y-axis and hν on the x-axis in the range of the Urbach tail would yield a straight line with a slope equals σ /kT and intersection with the y-axis equals (ln α o -σ hν o /kT).…”

Section: Urbach Rulementioning

confidence: 99%

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Gaffar¹,

El‐Fadl²,

Anooz³

2003

Cryst. Res. Technol.

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Optical absorption along the three crystallographic axes of (NH 4 ) 2 ZnCl 4 single crystals is reported over a temperature range from 276 K to 350 K. Our results clearly confirm the antiferroelectric to commensurate phase transition at 319 K. Analysis reveals that at the absorption edge the type of transition is the indirect allowed one. The indirect band gaps at various temperatures are determined and their temperature dependence is estimated in the antiferroelectric and commensurate phases. Optical parameters related to the temperature dependence of the energy gap are evaluated. The single-effective oscillator model was used to describe the imaginary part of the dielectric constant, which facilitate calculation of the dipole moment parameters. The steepness parameter is given, its value is used to estimate the temperature dependence of the indirect energy gap and the result is compared with that calculated graphically. In the region of the absorption edge, the absorption coefficient obeys Urbach's rule. Urbach characteristic parameters are determined and their temperature dependence is investigated. Correlation between different parameters is considered. Most of the results confirm the optical isotropic nature of AZC crystals.

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Section: Urbach Rulementioning

confidence: 99%

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Gaffar¹,

El‐Fadl²,

Anooz³

2003

Cryst. Res. Technol.

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“…where α 0 and E 0 are constants [21], their values depending upon crystal characteristics, and σ is a parameter which characterizes the broadening of the absorption edge due to the electron-phonon interaction or exciton-phonon interaction [22]. The Urbach tail [20] can be defined by plotting ln α versus hν Table 1.…”

Section: Broadening Of the Absorption Edgementioning

confidence: 99%

Temperature dependence of the indirect band gap and related optical parameters of (NH₄)₂ZnCl₄:xSr²⁺ single crystals

Gaffar

El‐Fadl

Anooz

2003

Physica Status Solidi (b)

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Optical transmittance measurements were carried out near the absorption edge of (NH 4 ) 2 ZnCl 4 : x Sr 2+ single crystals, where x = 0.00, 0.020, 0.039, 0.087 or 0.144 wt%. The dependence of the absorption coefficient (α) on photon energy in the range 3.4 -6.4 eV and on temperature in the range 276 -350 K was examined. With increasing temperature the absorption edge was shifted to the lower energy side; this shift was attributed to the temperature dependence of electron-lattice interactions. Due to the presence of Sr 2+ in (NH 4 ) 2 ZnCl 4 : x Sr 2+ a change in the absorption band centred at 5.30 eV was observed. In the case of higher strontium doping, the optical absorption coefficient showed a 'pre-transition' stage just before the onset of the band-to-band transition. Exponential dependence of α on hν according to the Urbach rule was observed and the Urbach parameters were determined. The steepness parameter was strongly affected by doping; its behaviour at 319 K evidently showed the antiferroelectric to commensurate phase transition. The temperature dependence of E g was also estimated using data for the steepness parameter, and hence E g at different temperatures and Sr 2+ concentrations was evaluated.

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“…The value of α as well as λ can be used to find the values of extinction coefficient, K by using the simple equation [39],…”

Section: Extinction Co-efficient Of Pf-abs Compositementioning

confidence: 99%

Fabrication and Optical Characterization of Palm Fiber Reinforced Acrylonitrile Butadiene Styrene Based Composites: Band Gap Studies

Neher¹,

Bhuiyan²,

Kabir³

et al. 2018

MSA

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The composite materials are replacing the conventional materials, owing to their excellent properties. The developments of new materials are on the anvil and are thriving day by day. Natural fiber composites such as palm fiber (PF) polymer composites became more enchanting because of their high specific strength, low weight and biodegradability. Mixing of natural fiber like PF with acrylonitrile butadiene styrene (ABS) polymer is finding increased applications. In this work, PF reinforced ABS composites PF-ABS was fabricated by Injection Moulding Machine. The effect of UV-Visible radiation on PF-ABS composites was studied by means of ultraviolet-visible spectroscopy in the wavelength 200 -1000 nm at room temperature. The present investigation shows that the addition of palm fiber modifies the absorption property of the materials. The absorption ability is maximal for 10% PF-ABS composites while minimal for 20% PF-ABS composites in the visible region of the spectrum. Optical constant like direct band gap energy, Urbach energy and Steepness parameter were determined using absorbance data. The values of direct energy band gap, Urbach energy as well as Steepness parameter were found to be in the range 2.6 -3.9 eV, 0.40 -0.85 eV and 0.03 -0.06, respectively. It was observed that the value of direct band gap energy as well as Urbach energy is higher while the value of Steepness parameter is lower for PF-ABS composites with 10% palm fiber.

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Ultraviolet Absorption of KI Diluted in KCl Cryst als

Cited by 234 publications

References 24 publications

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Temperature dependence of the indirect band gap and related optical parameters of (NH₄)₂ZnCl₄:xSr²⁺ single crystals

Fabrication and Optical Characterization of Palm Fiber Reinforced Acrylonitrile Butadiene Styrene Based Composites: Band Gap Studies

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Ultraviolet Absorption of KI Diluted in KCl Cryst als

Cited by 234 publications

References 24 publications

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Optical absorption spectra and related parameters of ammonium zinc chloride crystal in the antiferroelectric and commensurate phases

Temperature dependence of the indirect band gap and related optical parameters of (NH4)2ZnCl4:xSr2+ single crystals

Fabrication and Optical Characterization of Palm Fiber Reinforced Acrylonitrile Butadiene Styrene Based Composites: Band Gap Studies

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Temperature dependence of the indirect band gap and related optical parameters of (NH₄)₂ZnCl₄:xSr²⁺ single crystals