LASER-INDUCED MULTIPHOTON PHOTOCONDUCTIVITY IN DIRECT AND INDIRECT BAND GAP CRYSTALS USING Z-SCAN TECHNIQUE

2009 ◽  
Vol 23 (23) ◽  
pp. 2783-2789 ◽  
Author(s):  
ARUN GAUR ◽  
D. K. SHARMA ◽  
K. S. SINGH ◽  
NAGESHWAR SINGH
Keyword(s):  
Absorption Coefficient ◽  
Band Gap ◽  
Laser Pulses ◽  
Beam Waist ◽  
Photon Absorption ◽  
Nanosecond Laser ◽  
Direct Band Gap ◽  
Direct Band ◽  
Nanosecond Laser Pulses ◽  
Indirect Band Gap

Nanosecond laser pulses have employed the photoconductive Z-scan technique. Photoconductivity traces measured by moving the sample across the laser beam waist were used for measuring two and three-photon absorption processes. The value of the three-photon absorption coefficient β3=9.6×10-10 cm 3/ GW 2 in the case of direct, and 8.96×10-12 cm 3/ GW 2 and 5.0×10-12 cm 3/ GW 2 in the case of indirect band gap crystals have been estimated from a comparison of traces measured by exciting the sample with the first and second harmonics of Nd : YAG laser. The low value of β3 in the case of indirect band gap crystals compared to direct band gap crystals is attributed to phonon-assisted transitions.

Optical Studies of Poly (N-Carbazole) (PVK) Blending with Polyvinylpyrrolidone (PVP) Using Tauc/Davis-Mott Model

2013 ◽  
Vol 652-654 ◽  
pp. 527-531 ◽  
Author(s):  
A.N. Alias ◽  
T.I. Tunku Kudin ◽  
Z.M. Zabidi ◽  
M.K. Harun ◽  
Ab Malik Marwan Ali ◽  
...  
Keyword(s):  
Band Gap ◽  
Urbach Energy ◽  
Quartz Substrate ◽  
Optical Studies ◽  
Direct Band Gap ◽  
Mott Model ◽  
Blended Polymer ◽  
Electronic Parameters ◽  
Direct Band ◽  
Indirect Band Gap

The optical absorption spectra of blended poly (N-carbazole) (PVK) with polyvinylpyrrolidone (PVP) in various compositions are investigated. A doctor blade technique was used to coat the blended polymer on a quartz substrate. The electronic parameters such as absorption edge (Ee), allowed direct band gap (Ed), allowed indirect band gap (Ei), Urbach edge (Eu) and steepness parameter (γ) were calculated using Tauc/Davis-Mott Model. The results reveal that the Ee, Ed and Ei increase with increasing of PVP ratio. There also have variation changing in Urbach energy and steepness parameter.

scholarly journals Biaxial strain modulated the electronic structure of hydrogenated 2D tetragonal silicene

RSC Advances ◽  
2019 ◽  
Vol 9 (72) ◽  
pp. 42245-42251
Author(s):  
Haoran Tu ◽  
Jing Zhang ◽  
Zexuan Guo ◽  
Chunyan Xu
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Biaxial Strain ◽  
Direct Band Gap ◽  
Direct Band ◽  
Indirect Band Gap

Hydrogenation can open the band gap of 2D tetragonal silicene, α-SiH is semiconductors with a direct band gap of 2.436 eV whereas β-SiH is indirect band gap of 2.286 eV. The band gap of α-SiH, β-SiH and γ-SiH can be modulated via biaxial strain.

Optical limiting properties of BODIPY dyes substituted with styryl or vinylene groups on the nanosecond timescale

2019 ◽  
Vol 23 (07n08) ◽  
pp. 701-717 ◽  
Author(s):  
Nobuhle Ndebele ◽  
Zweli Hlatshwayo ◽  
Bokolombe P. Ngoy ◽  
Gugu Kubheka ◽  
John Mack ◽  
...  
Keyword(s):  
Thin Films ◽  
Absorption Coefficient ◽  
Laser Pulses ◽  
Optical Limiting ◽  
Nanosecond Laser ◽  
Third Order ◽  
The Third ◽  
Nanosecond Laser Pulses ◽  
532 Nm ◽  
Order Susceptibility

The results of recent studies on the optical limiting properties of BODIPY dyes at 532 and 1064 nm are described and compared. The optical limiting properties of novel 1,7-dimethyl-3,5-di-4-dihydroxyborylstyryl- and 3,5,7-tristyryl-1-methyl-BODIPY dyes were studied in CH2Cl2 and C6H6 and polystyrene thin films using the open aperture Z-scan technique at 532 nm with nanosecond laser pulses to provide an example of how the effective nonlinear absorption coefficient, the third order susceptibility, hyperpolarizability and limiting thresholds can be calculated.

SHIFT OF BAND GAP FROM DIRECT TO INDIRECT AND OPTICAL RESPONSE OF LiF UNDER PRESSURE

2013 ◽  
Vol 27 (09) ◽  
pp. 1350061 ◽  
Author(s):  
A. SAJID ◽  
G. MURTAZA ◽  
A. H. RESHAK
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Band Gap ◽  
Lithium Fluoride ◽  
Pressure Range ◽  
Pressure Effect ◽  
Indirect Transition ◽  
Direct Band Gap ◽  
Direct Band ◽  
Indirect Band Gap

We hereby are reporting the transition pressure at which lithium fluoride ( LiF ) compound transforms from direct band gap to indirect band gap insulator on the basis of FP-LAPW calculations. The fundamental band gap of LiF compound suffers direct to indirect transition at a pressure of 70 GPa. The study of the pressure effect on the optical properties e.g. dielectric function, reflectivity, refractive index and optical conductivity of LiF in the pressure between 0–100 GPa, shows that this pressure range is very critical for LiF compound as there are significant changes in the optical properties of this compound.

Single pot synthesis of indirect band gap 2D CsPb2Br5 nanosheets from direct band gap 3D CsPbBr3 nanocrystals and the origin of their luminescence properties

Nanoscale ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 4001-4007 ◽  
Author(s):  
Paribesh Acharyya ◽  
Provas Pal ◽  
Pralok K. Samanta ◽  
Arka Sarkar ◽  
Swapan K. Pati ◽  
...  
Keyword(s):  
Band Gap ◽  
Luminescence Properties ◽  
Direct Band Gap ◽  
Amine Complexes ◽  
Lead Bromide ◽  
Direct Band ◽  
Indirect Band Gap

The origin of the luminescence properties of CsPb2Br5 is ascribed to the presence of different amorphous lead bromide amine complexes.

Carbon nanotube: An indirect ~ 0 eV band gap material

2016 ◽  
pp. 3546-3550
Author(s):  
Maheshwar Sharon ◽  
S. S. Kawale ◽  
Rakesh Afre ◽  
Madhuri Sharon ◽  
C. H. Bhosale
Keyword(s):  
Thin Film ◽  
Carbon Nanotube ◽  
Band Gap ◽  
Carrier Concentration ◽  
Hydrogen Atmosphere ◽  
Sem Analysis ◽  
Direct Band Gap ◽  
Direct Band ◽  
Indirect Band Gap ◽  
First Time

Thin film of carbon was synthesized from camphor (C10H16O) by CVD technique in hydrogen atmosphere. For the first time it is confirmed the presence of almost zero indirect band gap in addition to its direct band gap.. Carrier concentration with intrinsic carbon is found to be around 1021 n/cm3. It is suggested that unless the zero indirect band gap is  increased carbon thin film   cannot be used for making a p:n junction. XRD, Raman and SEM analysis are performed.

Electronic State and Piezoresistivity Analysis of Zinc Oxide Nanowires for Force Sensing Devices

2015 ◽  
Vol 644 ◽  
pp. 16-21 ◽  
Author(s):  
Koichi Nakamura
Keyword(s):  
Band Gap ◽  
Compressive Strain ◽  
Force Sensing ◽  
Wall Structure ◽  
Direct Band Gap ◽  
Direct Band ◽  
The Difference ◽  
Piezoresistance Coefficient ◽  
Indirect Band Gap ◽  
P Type

The piezoresistivity for force sensing in wurtzite-ZnO nanowires with [0001] orientation has been simulated on the basis of the first-principles calculations of model structures. According to the difference in wall structure, our devised nanowire models can be divided into three groups by their conductivities; no band-gap conducting models, direct band-gap semiconducting models, and indirect band-gap semiconducting models. The strain responses to carrier conductivity of n-or p-doped semiconducting wurtzite-ZnO[0001] nanowire models were calculated using band carrier densities and their corresponding effective masses derived from the one-dimensional band diagram by our original procedure for a small amount of carrier occupation. The conductivities of p-type direct band-gap models change drastically due to longitudinal uniaxial strain in the simulation: the longitudinal piezoresistance coefficient is 120 × 10–11 Pa–1 for p-type (ZnO)24 nanowire model with 1% compressive strain at room temperature.

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