2. Experimental details
2.1. Instrumentation
Edinburgh spectrofluorimeter, model FLS920, which has a
450 W xenon lamp source, was used for recording the steady state
luminescence spectra. Fused silica cuvette of path length 2 mm
was used as a sample cell for recording the luminescence spectra.
The band pass of 3 nm was set for each excitation as well as for
emission monochromator. A long-wavelength pass filter (UV–39,
Shimadzu), with a maximum and uniform transmittance (485%)
above 400 nm, was placed in front of the emission monochromator,
in order to reduce the scatter of the incident beam into the
emission monochromator. Spectra were recorded at room temperature
with a 901 collection geometry.
Time resolved spectra of the excited states were recorded using
the same instrument with a ms-Xe flash lamp. Luminescence decay
times were determined by fitting the observed time resolved
luminescence signals to an exponential decay function. A single
exponential fit was found to be adequate for the decay processes
observed in this study. The χ2 values of all the fits ranged between
0.9 and 1.1. The relative standard deviation of the lifetime values
was less than 5%.
UV–vis absorption spectra were recorded at room temperature
using an Avantes fiber optic spectrophotometer (AvaSpec-3648-
USB2) with 300 lines per mm grating. An integration time of 6 ms
was used and 20 spectra were averaged to improve the signal to
noise ratio. Fused silica cuvette of path length 10 mm was used as
a sample cell for recording the absorption spectra.