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 ( 4 85%)
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.