Experimental Verification of the Accuracy of Oxygen-Varying Correlated Fluorescence for Determining the Quenching Constant K_SV

The oxygen-varying correlated fluorescence provides an effective strategy to gain the quenching constant K_SV for a non-phosphorescent system. Owing to the absence of detectable phosphorescence emission in general optical spectroscopy, the facticity of this method has never been verified. Here, the correct way to determine K_SV by oxygen-varying correlated fluorescence was systematically studied in detail. We selected gadolinium protoporphyrin IX (Gd-PpIX) to establish a fluorescence and phosphorescence dual emission system. Then, K_SV of Gd-PpIX can be obtained by the change of fluorescence intensity (I_F) with oxygen concentration using the method of correlated fluorescence at intense pump power; meanwhile, the value can also be determined from the relationship of the phosphorescence intensity ratio and oxygen content by the Stern-Volmer equation under relatively low power density. It was found that the K_SV values obtained by the above two methods were 12.2(1) and 11.9(7) kPa^-1, respectively. Our results successfully verified the accuracy of oxygen-varying correlated fluorescence for determining the K_SV by the phosphorescence property and fluorescence saturation of Gd-PpIX.