Abstract
The activation and deactivation of photochromic TRANSITIONS SIGNATURE (R) VII lens under extreme exposure to ultraviolet radiation of 222 W/m(2) for more than 144 h are scrutinized. The photoluminescence (PL) spectra upon excitation with ultraviolet radiation of different wave-lengths have been investigated. The obtained results show that photochromic TRANSITIONS SIGNATURE (R) VII gray lenses blocked ultraviolet radiation from 190 nm to 400 nm. The absorbance increases from 0.021 to be about 0.44 upon exposure to ultraviolet radiation of 302 nm for 144 h. The deactivation rate is decreasing exponentially with elapsed time; the absorbance reduces to be half after 5 min. Under extreme exposure to ultraviolet radiation of 302 nm the lens transmittance dynamic range reduces from 21.10 to be 7.20, also the optical band gap is insignificantly decreased from 2.913 eV to 2.869 eV indicating that the lens is non-degradable. TRANSITIONS SIGNATURE (R) VII lens was irradiated with ultraviolet radiation in the wave-length range from 260 to 400 nm and the photoluminescence (PL) emission spectra were measured. A strong correlation between the PL spectra and the excitation wavelength of ultra-violet radiation was observed. Both the PL integrated area under the peak and its band peak height are associated with the excitation wavelength, peaking at 275 nm and 385 nm, respectively, and then decreasing as the ultraviolet radiation wavelength increased. These results demonstrate that TRANSITIONS SIGNATURE (R) VII lenses are resistant to all ultraviolet radiation as well as blue light where Chromea7TM is activated.