Exciton formation (IMAGE) City University of Hong Kong Caption Illustration of exciton formation using light energy. In metal, an exciton is believed to form when the hole left by an excited electron pairs up with an electron at the Fermi level. Credit City University of Hong Kong Usage Restrictions Image must be used with appropriate caption and credit. License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.