I explain it better. If we bring an electron from higher to lower energy level, the energy gap will be emitted as electromagnetic wave, because of the conservation of energy. When the same situation applies for a physical body, for example letting if falling down from some height, what does it emit while losing its energy? My answer would be: it it just emits what it received to increase its energy. Namely the electron was excited by a wave, so it emits wave by losing energy.