Answer
1.7 eV
Work Step by Step
The wavelength of the photon that is emitted has an energy equal to the energy gap.
$$E_g=hf=\frac{hc}{\lambda}$$
$$=\frac{(6.63\times10^{-34}J \cdot s)(3.00\times10^8m/s)}{(1.60\times10^{-19}J/eV)(730\times10^{-9}m)}$$
$$=1.7 eV$$