The application relates to determining the amount of a predetermined type of radiation irradiated on a sensor material by: a) providing a sensor material; b) exposing the sensor material to the predetermined type of radiation for retaining the predetermined type of radiation in the sensor material for a predetermined period of time; c) subjecting the sensor material, which has been exposed to the predetermined type of radiation, to heat treatment and/or to optical stimulation; and d) determining the amount of visible light emitted by the sensor material as a result of being subjected to the heat treatment and/or to the optical stimulation; wherein the sensor material is represented by the following formula (I).