4. Conclusions
In summary, through measurements of the frequency upconversion fluorescence spectra and the fluorescence emission versus excitation intensity, 3PA of the two compounds was demonstrated. The 3PA-induced frequency upconversion fluorescence intensity is cubic with the input intensity. The electron donor has great impact on the upconversion fluorescence spectra. A strong donor strength can decrease the fluorescence intensity and split the energy level, and prolong the fluorescence lifetime. The 3PA-induced frequency upconversion fluorescence intensity is not in proportion to 3PA cross-section, but a larger 3PA cross-section corresponds to a stronger upconversion fluorescence emission. The fluorescence lifetime and components of the two compounds were measured indirectly: 97.4% is 1.309 ns and 2.6% is 50.754 ns for A at 495 nm, and only one component 0.903 ns for B at 420 nm. The theoretical calculations are consistent with the experimental results.
Acknowledgments
This work is supported by the Project of Provincial University Fundamental Research of Henan Province and the Project of Scientific and technological research of Henan Province (NO. 142102210035).