Question

For LED's to emit light in visible region of electromagnetic light, it should have energy band gap in the range of :

• A. $0.1eV$ to $0.4eV$
• B. $0.5eV$ to $0.8eV$
• C. $0.9eV$ to $1.6eV$
• D. $1.7eV$ to $3.0eV$

Answer 1

The correct option is D $1.7eV$ to $3.0eV$

The wavelength of electromagnetic radiation for it to lie in the visible region should lie in the range of $4000A-7000A$.
Using, $E=$$\frac{hc}{\lambda }$
and substituting the value of $\lambda$ into the equation, we get the value of $E$ to lie in between $1.7$ to $3eV$