5. Below is a transmission versus wavelength series of Zn chalcogenide windows o

Question

5. Below is a transmission versus wavelength series of Zn chalcogenide windows of similar thickncss The right figure is a blow-up of the short wavelength side. Also shown is a portion of the periodic table showing the column of chalcogenides. Using t (18 pts total) these graphs, answer the following questions. A)(B) 2n3 Se Wavelength lm Wavelength m a) Which of the materials, ZnO, ZnS, or ZnSe, has the best broad-band transmission? (2) b) Which of the materials, ZnO, ZnS, or ZnSe, has the largest refractive index? (2) c Given the graphs above, and the fact that pure ZnO and ZnS are colorless, and ZnSe is yellowish- orange, which of the 3 has the SMALLEST band-gap? (2) d) Which has the bigger bandgap, ZnO or ZnS? (2) e) The low transmission on the right-hand side of graph (A), i.e, at long wavelengths, is due to which of the following: reflection, absorption, scattering? (2) f) What is the underlying physical mechanism of thc phenomenon you listed for e) above? (2)

Explanation / Answer

a)According to the graph ,ZnO has high transmittance w.r.to smaller wavelength. That mean it transmit more in lower region . That makes it has a best broad band property.

b)For refractive index , we consider the distance travelled by light through glass . So as per the transmittance method zno has largest refractive index.

c)For smaller band gap,in ZnO ,ZnS and ZnSe ,we have calculated band gap with tauc plot in we found that ZnSe has smallest band gap .

d)And in between ZnO and ZnS , ZnS has bigger band gap . There is method followed are transmittance method for gett ing the correct answer.

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