Optical limiting and nonlinear absorption of excited states inmetalloporphyrin-doped sol gels

摘要

Optical limiting and upconverted luminescence have been studied inndifferent chromophore-doped aluminosilicate gel materials and theneffects of the dynamic processes from different central ions arendiscussed. Chromophores are metalloporphyrins ofntetra-4-sulfonatophenylporphyrinato-copper(II) andntetra-4-sulfonatopfienylporphgrinato-zinc(II) (CuTPPS and ZnTPPS,nrespectively) which are embedded in aluminosilicate gel hosts.nPhoto-upconverted luminescence was observed and believed to result fromnthe radiative recombination of the second excited singlet state.nSaturated behavior of upconverted emission was found as a function ofnincident excitation intensity. An optical limiting phenomenon associatednwith reverse saturated absorption was studied. These effects arenattributed to higher excited state, absorption. The observation ofnupconverted luminescence indicates that the upper excited statenabsorption occurs while nonlinear absorption is being observed. Dynamicnanalysis of excited state processes indicates that intersystem crossingnand triplet-triplet (quartet-quartet) absorption dominates nonlinearnprocesses and suggests that saturation absorption or reverse saturationnabsorption is dependent on the ratio of the effective absorption crossnsection for the excited states to that for the ground state. Absorptionncross sections for the excited states are estimated by the data fittingnto upconverted emission intensity and nonlinear absorption