For example, the maximum gain can occur at {HEAD ~ an energy} at or below {TAIL ~ the maximum band gap emission} 
at
For example , the maximum gain can occur at { HEAD ~ an energy } at or below { TAIL ~ the maximum band gap emission }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL