Second harmonic generation in SiO2 sol–gel films functionalized with Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) molecules

Abstract High concentrations of Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) chromophores were linked covalently to two different kinds of SiO 2 matrices prepared by the sol–gel method. The matrices differed in their reticulation level, determined by the organometallic precursor used during the synthesis. The materials were deposited as films by spin-coating. The chromophores in the films were oriented in a non-centrosymmetric way by a modified Corona poling set-up, and the nonresonant second order non-linear optical coefficient d 33 (0) of the films was determined by means of the Maker fringe technique. It was found that there is an optimum concentration of chromophores for attaining the highest d 33 (0) value in these materials. Their maximum d 33 (0) value was found in the films with the least reticulated matrix, that value was equal to 5.2 ± 0.5 pm/V. Besides, the d 33 (0) value was more stable in time in the less reticulated materials.