indicating high excited state density of the ZnO nanocrystals Moreover no bleaching feature can be found in this wide range meaning no sign of filling of permanent trap states怎么理解

This passage is describing the behavior of ZnO nanocrystals under certain conditions. The "excited state density" refers to the number of electrons that have been excited to a higher energy level than their ground state. The passage is saying that there is a high density of these excited electrons in the ZnO nanocrystals.

The "bleaching feature" refers to a phenomenon where the absorption of light decreases over time as trap states are filled. However, the passage is saying that no such feature can be found in this case, indicating that there are no permanent trap states being filled. In other words, the excited state density is not being reduced by any trapping of the excited electrons