Effects of excitation power density on the Stern-Volmer constant measurement

The Stern-Volmer constant (K-SV) is an important parame-ter to describe the capability of energy transfer to oxygen for porphyrin and its derivatives. By fitting Stern-Volmer equation, I-P0/I-P = 1 +K-SV[O-2], the KSV is generally deter-mined through phosphorescence intensities (IP) under aer-obic and oxygen-free conditions. In this work, the effect of excitation power density on the K-SV measurement is theoretically analyzed and experimentally studied, using pal-ladium octaethylporphyrin (PdOEP) as an example. The I(P )of PdOEP increased nonlinearly with excitation power density, and the power dependent slope of IP0/IP could be obtained. By way of the functional relationship between the slope of I-P0/I-P and power density, the real KSV of PdOEP was fitted to be 58 +/- 2 kPa(-1). The oxygen-dependent phosphorescence lifetimes (tau P) and IP under a weak excitation power are also measured to calculate the real KSV, which verifies our analysis. (c) 2023 Optica Publishing Group