The frequency of the incident radiation and not its intensity is the criterion for photoelectric effect. The lowest frequency of electromagnetic waves that can cause photoemission is about 4.6 × 1014 Hz (for the alkali metal caesium). Since radio waves have frequencies 1 GHz or lower, they cannot cause photoemission.
Only alkali metals are photosensitive to visible light; other metals are photosensitive only to far ultraviolet radiations.
