Stimulated luminescence from chromate ions adsorbed on disperse silica surfaces under intense ultraviolet excitation

Luminescence measurements of chromate ions (CrO42-) adsorbed onto disperse silica (SiO2) surfaces under intense pulsed ultraviolet excitation (lambda(exc) = 354.7 or 266 nm, tau(p) = 20 ns) were performed at room temperature. The luminescence spectra were collected for different values of the excitation intensity (I). The luminescence yield in the red band corresponding to emission from CrO42- ions varies linearly with I under 354.7 nm excitation. However, the intensity dependence of the luminescence yield under 266 nm excitation is characterized by a threshold (I similar to 0.6 x 10(6) W cm(-2)), after which the intensity dependence of the luminescence yield is described by a power law with index n = 1.7 and then saturated at I similar to 1.0 x 10(6) W cm(-2) This feature of the excitation dynamics has been attributed to stimulated emission and considered by means of a four-level scheme. The cross section of stimulated emission was estimated as similar to 3.3 x 10(-21) cm(2). (C) 1997 American Institute of Physics.