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.