Silver can reflect over 99 percent of light (photons) but at the speed of light reasonable size containers reflect millions of times a day, each time heat is generated by the silvers outer electron orbits absorption of energy. You could give the silver an electric charge, the silver container would then create a magnetic field and your container would begin to ring or vibrate to the frequencies of the light. Also once the air or gas in the container absorbs all the energy or photons it can it would explode or become a plasma. Plasma is even harder to contain. (forth state of matter).
Your sons idea is called a maser or laser, only single frequency light can be amplified or stored without losing most of it to friction, mirrors or a container not of a frequencies length causes heat (as does all interactions of energy with physical containers.) To create a container without reflection, refraction or any type of friction is called a cyclotron or atom smasher. Atomic energy can amplify the photons using the weak or strong nuclear forces, but that get messy.