Date of Award

Spring 1986

Document Type

Thesis

Department

Electrical & Computer Engineering

Program/Concentration

Electrical Engineering

Committee Director

Amin N. Dharamsi

Committee Member

Karl H. Schoenbach

Committee Member

Joseph L. Hibey

Call Number for Print

Special Collections LD4331.E55J66

Abstract

A pump and probe technique was used to investigate triplet-triplet excited state absorption in solutions of the scintillators 2,5 diphenyloxazole (PPO) and 2,1 naphthyl,5 phenylzole (a-NPO) in several solvents.

KrF excimer radiation (248 nm) was used to pump the samples under investigation as well as a tunable dye laser which was used as the probe. Time-resolution was obtained by changing the optical path difference between the pump and probe beams.

Transient excited state absorption was measured in a wide spectral region between 330 nm and 600 nm, showing a peak at 400 nm for PPO solutions, and two peaks at 390 nm and 455nm respectively for a-NPO solutions. After the excimer pump excited the sample, the absorption peaked approximately respectively. 110 ns and 60 ns for PPO and a - NPO. Fluorescence from the S1 ->S0 band was monitored simultaneously.

The effect of varying concentrations (in the range 10 -1 M and 10 -7 M) was investigated. Both the fluorescence and excited state absorption displayed a concentration quenching effect for PPO in cyclohexane and 1,4 dioxane, and for a -NPO in 1,4 dioxane. The maxima occurred at approximately 10 -3 M. No such self-quenching was observed for toluene solutions.

A numerical analysis of the relevant rate equations for the molecular excitations and deexcitation processes was performed. This analysis yielded some rate constants that have not been measured previously. For example: K the intersystem crossing rate for PPO was found to be 2.9 x 10 6 sec -1 and that for a-NPO to be 3.3 x 10 6 sec -1 ; K, the excimer formation for a-NPO was measured as 7 e. 5 x 10 -12 cm 3 – sec -1 ; K tr the quenching by O 2 of PPO triplets is 1.6 x 10 5 sec -1 while a- NPO it is 2.5 x 10 6 sec -1 . K, the triplet-triplet self-quenching rate for PPO is 3.2 x 10 -12 cm 3 -sec -1 and for a-NPO it is 6.8 x 10 -12 cm 3 -sec -1 .

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DOI

10.25777/h410-d874

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