PHOTO-SENSITIVE ELEMENT FOR INDICATING THE EXPOSURE TO ULTRAVIOLET RADIATION AND METHOD FOR PRODUCING SAID PHOTO-SENSITIVE ELEMENT

摘要

The present invention relates to a photo-sensitive element used for indicating the exposure to ultraviolet radiation, wherein the colour or transparency of said element changes in the visible spectrum due to the action of said ultraviolet radiation. This element is characterised in that it is made of an alkaline-halide monocrystal of the potassium family, wherein said crystal is doped using sensitising dopants that contain calcium cations. The proportion of the alkaline-halide monocrystal of the potassium family ranges from 99.9990 to 99.9999 wt.%, while that of the calcium cations ranges from 0.001 to 0.01 wt.%. The alkaline-halide monocrystal of the potassium family may for example consist in iodinated potassium or in chlorinated potassium. This invention also relates to a method for producing this photo-sensitive element for indicating the exposure to ultraviolet radiation, wherein said method involves growing a alkaline-halide monocrystal of the potassium family from an alloy and applying a thermal treatment in vapours of an alkaline metal. This method is characterised in that calcium is added to the alloy during the growth process. The thermal treatment is carried out in one step at a temperature of between 500 and 580 DEG C for a duration of between 4 and 6 hours, and the monocrystal is then cooled down at a temperature of between 400 and 450 DEG C at a rate not exceeding 1 to 2 degrees per minute. The crystal is further maintained at a temperature of between 400 and 450 DEG C for at least one hour and finally cooled down at a temperature of between 18 and 25 DEG C at a rate not exceeding 1 to 2 degrees per minute.