From Special theory of relativity we know that $E=m_0 c^2$, which says about mass energy equivalency. But my question : **Is there any real experiment where some mass is created purely from energy? **
Sufficiently high energy photon can spontaneously convert into a pair of leptons as long as there is a heavy charged spectator (i.e. an atomic nucleus) nearby to absorb some momentum. This is the largest energy-loss mechanism for very energetic photons in high $A$ materials.
You can also get two-photon interaction to ends with massive particles in the final state, but that is suppressed by a coupling constant relative the single-photon plus spectator case.