26698
We combined X - ray absorption fine structure and photoluminescence measurements to analyze the structure of europium centers in ( Ca , Eu ) 2SiS4 luminescent powders .
 europium, ( Ca , Eu ) 2SiS4
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 europium, ( Ca , Eu ) 2SiS4