The material gets extra energy and emits waves.

Thus, a black material can absorb and emit energy faster than the white material.

Thus, the material emits radiation, which has energy characteristic of the atoms present.

Flash point: Lowest temperature at which a material will emit vapor combustible in air mixture.

This is radiation: the hot material emits particles or waves of energy that then travel to the cold object and are absorbed.

The material in the disc gets very hot because of friction, and emits X-rays.

Depleted of its most radioactive part for use in nuclear fuel, the material still emits low-level radiation.

This porous material could emit visible light when a current was passed through it (electroluminescence.

Having said that, any material with a temperature above absolute zero emits electromagnetic energy.

Electroluminescence - The phenomenon where a material emits light in response to an electric current passed through it, or to a strong electric field.