Physicist, one sparkling in interviews (5)
I believe the answer is:
joule
'physicist' is the definition.
(James Prescott Joule)
'one sparkling in interviews' is the wordplay.
'one sparkling' becomes 'jewel' (a sparkling object).
'in interviews' indicates a 'sounds like' (homophone) clue (how the word might sound in an interview).
'jewel' is a homophone of 'JOULE'.
(Other definitions for joule that I've seen before include "SI unit of work/energy" , "SI unit of energy" , "physicist" .)