The spectrum and the decay time of the excimer luminescence in very thin tetraphenylporphyrin (H2TPP) films evaporated on SnO2 substrates have been measured in situ at a pressure of 2 × 10-6Pa at 100K using a picosecond dye laser. The decay time of the 665 nm luminescence in H2TPP on a highly conductive SnO2 (σ = 77 Ω-1 cm-1) is 800 ps in films with a thickness above 25 Å and decreases with decreasing thickness to 170 ps at 7.5 Å. On the other hand, the decay time in the films on a low conductive SnO2 (σ = 4.5 x 10-3 Ω-1 cm-1) is dependent of film thickness. It is found that luminenscence quenching occurs through the excimer state because of the coincidence in the quenching ratios calculated from the decay time and the luminiscence intensity. We propose a mechanism where an excited electron is transferred from the excimer state of H2TPP to the conduction band of the highly conductive SnO2 substrate.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Condensed Matter Physics