Raised issue, period (4)
I believe the answer is:
time
'period' is the definition.
(period of time)
'raised issue' is the wordplay.
'raised' is a reversal indicator (going up in a down clue).
'issue' becomes 'emit' (both can mean to give out or radiate).
'emit' written backwards gives 'TIME'.
(Other definitions for time that I've seen before include "it may be Central European" , "Tempo; occasion" , "Age" , "See 12" , "Pub closing call" .)