Given that the level of energy of the acceptor band is above the valence band by, 
$\mathrm{E}=57 \mathrm{meV}$
The energy of the photon having just enough energy to overcome the gap is given by, 
$\mathrm{E}=\frac{\mathrm{hc}}{\mathrm{\lambda }}$
$\Rightarrow \mathrm{\lambda }=\frac{\mathrm{hc}}{\mathrm{E}}$

Speed of light  $\mathrm{c}=3\times {10}^8 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{$\mathrm{s}$}\right.$
Planck's constant $\mathrm{h}=6.63\times {10}^{-34} \mathrm{Js}$, 

Substituting values,
$$\begin{gathered} \mathrm{\lambda }=\frac{6.6\times {10}^{-34}\times 3\times {10}^8}{57\times {10}^{-3}\times 1.6\times {10}^{-19}} \\ \mathrm{\lambda }=21700\stackrel{\circ }{\mathrm{A}} \end{gathered}$$

The maximum wavelength of light required to produce a hole is$\mathrm{\lambda }=21700 \stackrel{\circ }{\mathrm{A}}$ .