Scientist do not fully  understand this phenomenon, but have  some ideas as to why this is happening. It is thought to be attributable to the oxidative aging that occurs during the hardening of the outer shell of the scorpion. The hardening of the cuticle layer which is the outer shell is called  sclerotization and along with it comes the oxidative aging of proteins  which may have caused the increase in florescence of the scorpion as shown.