24508
In developing different UCNPs , the characterization of their quantum yield ( QY ) is a crucial issue , as the typically drastic decrease in QY for low excitation power densities can either impose a severe limitation or provide an opportunity in many applications .
 None
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None