Unlike "triboluminescence" which does not require additional excitation source other than force itself, ML is often manifested by external photoexcitation such as a UV lamp.
For example, a certain boron complex of sunscreen compound avobenzone exhibits reversible ML.
A recent detailed study[2] suggests that ML from the boron complex consists of two critical coupled steps: 1) generation of low energy exciton trap via mechanical perturbation; and 2) exciton migration from regions where photoexcitation results in a higher excited state.
Since solid-state energy transfer can be very efficient, only a small fraction of the low-energy exciton traps is required when mechanical force is applied.
As a result, for crystalline ML materials, XRD measurement may not able to detect changes before and after mechanical stimuli while its photoluminescence can be quite different.