The decay constants
k
T
for phosphorescence and
k
D
for delayed fluorescence have been measured for the same outgassed solutions of acenaphthene, pyrene, 1,2-benzanthracene and fluoranthene in liquid paraffin over a range of temperatures between – 70 and 30 °C. In all cases the luminescence decay is exponential and the intensity of delayed fluorescence is found to vary as the second power of incident light intensity; under these conditions the relation
k
D
= 2
k
T
required by the triplet-triplet annihilation origin of delayed fluorescence is established over the temperature ranges in which delayed fluorescence and phosphorescence are exhibited simultaneously. Diffusional quenching of the triplet state
3
A
by a solute impurity
Q
is believed to be responsible for the temperature (viscosity) dependence of
k
T
and
k
D
since (
a
)
k
T
and
k
D
are linear functions of solute concentration where this is examined, (
b
) by taking account of the reversibility of the quenching process
3
A
+
Q
⇌
A
+
3
Q
at higher temperatures (lower viscosities) the virtual independence of
k
on temperature exhibited for 1,2-benzanthracene and fluoranthene under these conditions may be explained. The resumed temperature dependence of
k
D
for fluoranthrene at still higher temperatures is attributed to endothermic quenching of the triplet state by an impurity with a higher triplet state than that of the solute.
Toxicant Induced Changes on Delayed Fluorescence Decay Kinetics of Cyanobacteria and Green Algae: A Rapid and Sensitive Biotest
