My friend told me crystal materials only have luminescence properties. Is it right?
The photoluminescence intensity increases with the improvement in the crystallinity of the material.
Not only in crystals, PL is observed in non- crystalline chalcogenide glasses also even without putting any impurities. The intensity is , however, lower in these materials. The structural defects introduced during quenching are responsible for PL spectrum. PL studies has been quite useful in the study of defect states in these glasses.
This question cannot be answered in general. Just to give you an example, organic materials span a wide range of actual molecules possible. Among them you find both high PLQY crystals (where luminescence efficiency goes down towards amorphous systems of the same molecular species) and high PLQY fully amorphous layers of organic molecules on the other side. As Mr. Naziruddin pointed out, there are coupling scenarios (aggregation induced) where intensity goes up but not necessarily simply because of crystallinity.
It is a matter of the transission causing the PL band. If you observe an atomic transission, it is not that strongly affected by the surrounding material quality. A good example for this is Cr in sapphire. If you talk about bulk transitions like electron-hole-recombinations in semiconductors, any defect (surface, grain boundaries, dislocations, impurity atoms, stacking faults, strain, ...) affects in principle your emission by changing the emission energy or by completely destroying all luminescence properties.
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