The phenomena of luminescence were discussed on the basic of reaction of radiation with matter. Impurities in crystal have essential effects upon crystal luminescence- Two mechanisms are found in crystal luminescence. One is the irradiation induced luminescence which will vary with the irradiation doses the crystal received. The other is non-irradiation related

such luminescence is depend on impurities in crystal. The superlinearity correction part of equivalent dose method in TL dating belongs to the non-irradiation type

so such correction is unnecessary.