When ions pass through a crystal channel, they do not only feel a continuous potential of “atomic string”, but also an oscillatory electric field with a frequency equal to the ion velocity,v, divided by atomic spacing along the atomic string,d.Okorokov predicted that, if the electron of the ion has an excited state resonating with the frequency or one of its high harmonicsv= kv/d(k = 1, 2, …), it will be excited during the passage through the crystal channel and the ion emits a photon due to the deexcitation. The present author and coworkers observed first time the Kα X-rays from Ne9+and F8+ions channeled along the (111) and (110) axes of a gold crystal, respectively. In the present report, the possibility of the photon emission from the channeled heavy ions excited by the Okorokov effect is discussed and the experiments on the photon emission are surveyed.