Indirect Optical Band Gap Energy Research Articles

Synthesis and characterization of Mg 2B 2O 5

Magnesium borate of the form Mg 2B 2O 5 has been prepared and its structural and thermal properties were studied using X-ray diffraction and differential thermal analysis. An investigation of the electrical and optical properties of Mg 2B 2O 5 system has been carried out. The electrical resistivity of the sample was measured in the temperature range of 170–400 K. The data analysis revealed an extrinsic nature of the conductivity with two impurity levels located at 0.13 and 0.71 eV in the temperature ranges of 170–230 K and 240–400 K, respectively. The optical transmission and reflection was recorded at 300 K in the incident photon energy range of 3.0–6.0 eV. The absorption coefficient data analysis revealed an indirect optical energy band gap of 4.73 eV. In addition, two impurity levels located at 3.43, and 4.49 eV were observed in the absorption spectra.

A Study on Structural and Optical Properties of Pb1-xCdxI2 Single Crystals

<TEX>$Pb_{1-x}$</TEX> <TEX>$Cd_{x}$</TEX> <TEX>$I_2$</TEX> (x=0.0, 0.2, 0.5, 0.7, 0.9, 1.0) single crystals were grown by using Bridgman method and their structural and optical properties were investigated from the measurement of X-ray diffraction, optical absorption and photoluminescence. As-grown single crystals have hexagonal closed packed layered structure. The values of lattice constant c decrease with increasing composition x. Direct and indirect transition optical energy band gaps are calculated from optical absorption spectra measured at room temperature. They increase exponentially from 2.3eV to 3.2 eV with increasing composition x. The energies of photoluminescence peak due to donor bound exciton measured at 6K increase with increasing composition . However, the peak energies of donor-acceptor pair (DAP) are independent of the optical energy band gaps of <TEX>$Pb_{1-x}$</TEX>/<TEX>$Cd_{x}$</TEX> <TEX>$I_2$</TEX> single crystals.

Optical properties of β-In2S3 andβ-In2S3:Co2+ single crystals

β-In2S3 and β-In2S3:Co2+ singlecrystals were grown by the chemical transport reaction method usingIn2S3, S, and ZnS as starting materials and (ZnCl2 + I2) asa transport agent. The single crystals crystallized into a tetragonalstructure. The indirect optical energy band gaps of the single crystals at 298 Kwere found to be 2.240 eV and 1.814 eV for β-In2S3 andβ-In2S3:Co2+, respectively. The direct opticalenergy band gaps were found to be 2.639 eV and 2.175 eV for β-In2S3and β-In2S3:Co2+, respectively. Impurity optical absorptionpeaks were observed for the β-In2S3:Co2+ single crystal.These impurity absorption peaks were assigned, based on the crystal fieldtheory, to the electron transitions between the energy levels of the Co2+ion sited in Td symmetry.