Presently i am working on graphene materials. i have confusion.ie how much quantity of the material (solid in grams) i need to take and volume of the solvent. what is the ratio (W/V).
how can we measure the transmittance and reflectance of the materials ?
In UV measurement, absorbance is directly proportional to the concentration of the solution. However, for practical purpose, your solution should be transparent and a very little amount should be added so that particles are well dispersed in the solvent say you can add 0.5g in 5 ml, it it still appears to be translucent then you can dilute it.
The band gaps can be calculated via UV-Vis spectroscopy using Tauc Plots. By plotting the graph between (ahv)^(1/2) versus photon energy (hv) where, a (alpha) is the absorbance calculated from UV . (hv) can be calculated form wavelength using: (hv = 1240/wavelength);Extrapolating the straight line portion of the curves to zero absorption coefficient value gives the energy band gap value.
Yes, band gap can be calculated using tauc plots. For calculating indirect bandgap calculation, plot between (ahv)^(1/2) versus photon energy (hv) as mentioned by renuka and for direct band gap calculation plot (ahv)^2 versus photon energy (hv) . The intercept of tangent to the x-axis gives the value of band gap of material.
The optical band gap (Eg, in eV) can be calculated using absorption edge values (λ edge, in nm) from absorption spectra by using eq
Eg= 1240/ λ edge.
Here you can find good explanation and band gap calculator,
http://www.instanano.com/characterization/theoretical/uv-vis-spectroscopy-band-gap-calculation/
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