Question

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

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

Answer 1

The correct option is C $1.7\text{eV}\text{to}3.0\text{eV}$

The wavelength of visible light lies in the range of $4000\mathring{\text{A}}\text{to}7000\mathring{\text{A}}$. The energy gap is equal to the energy of the emitted photon.

So, minimun energy for visible light is

$E_{min}=\frac{hC}{{\lambda }_R}=\frac{12400}{7000}=1.7\text{eV}$

And, maximum energy for visible light is,

$E_{max}=\frac{hC}{{\lambda }_V}=\frac{12400}{4000}=3.1\text{eV}$

Hence, $\left(C\right)$ is the correct answer.