The photoluminescence (PL) spectra excited at
247 nm and photoluminescence excitation (PLE) spectra monitored at 694 nm radiation are determined by an Edinburgh FLS920 spectrofluorometer by using a 450 W Xe lamp as the light source at room temperature, and excitation and emission slit-widths are both set at 1 nm. The morphology and size of the samples are observed with a Hitachi S4800 scanning electron microscope (SEM) with an operating voltage of 20 kV. The transmittance spectra of the films in the wavelength range 200–900 nm are determined with a Hitachi UV-3310 spectrophotometer.