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December 19, 2014

Homework Help: chemistry

Posted by Anonymous on Friday, December 14, 2012 at 4:19am.

The glass panels of a sky roof need to be coated in order to screen out ultraviolet radiation (10-400 nm wavelength) but without color distortion in the visible spectrum. Candidate coating materials are gallium nitride (GaN) with a band gap,Eg, of 3.2 eV, or gallium arsenide (GaAs) with a band gap, Eg, of 1.34 eV. Choose the best explanation for which of these materials, if either, will work.

DATA: representative wavelengths associated with different colors in the visible spectrum:
violet 425 nm
blue 475 nm
green 535 nm
yellow 590 nm
orange 610 nm
red 700 nm

GaAs is the best choice, it has a band gap low enough to block out UV radiation while allowing visible light to pass.

GaN is the best choice, it has a band gap low enough to block out UV radiation while allowing visible light to pass.

Neither will work, due to the electromagnetic spectrum any material that blocks out UV radiation will also block out visible light, this is why sunscreen and sunglasses tend to be somewhat opaque.

Neither will work, UV light will be able to pass through both of them if visible light is able to pass through as well.

Neither will work, visible light has energy greater than 3 eV and the semiconductors will be opaque.

Both will work, visible light has energy lower than 1 eV and is able to pass through both materials unaltered.

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