Ionised gas: contrived a sample to emit energy (6)
I believe the answer is:
plasma
'ionised gas' is the definition.
(I've seen this before)
'contrived a sample to emit energy' is the wordplay.
'contrived' indicates an anagram.
'to emit' indicates named letters should be taken away.
'energy' becomes 'e' (physics symbol as in E=mc2).
'sample' with 'e' taken away is 'sampl'.
'a'+'sampl'='asampl'
'asampl' with letters rearranged gives 'PLASMA'.
(Other definitions for plasma that I've seen before include "Colourless fluid in blood; green variety of quartz" , "Ionised gas; fluid in blood" , "TV screen type" , "The watery part of the blood" , "Yellow liquid in blood" .)