Flexible-composition-dependent third-order nonlinear optical properties of sol-gel-derived amorphous oxide glasses

The ever-increasing demands of high-performance nonlinear optical (NLO) electronic and optoelectronic devices promote the investigation of the compatibility of the NLO characteristics of solid-state matrix hosts and doped functional components. In this work, we developed a facile and efficient sol-gel wet chemical method for preparing stable and transparent monolithic oxide glasses exhibiting controllable NLO responses by collaboratively designing the glassy composition, which can be readily applied to solid-state matrices to encapsulate NLO components. We systematically characterized the structures and compositions of the glasses. The linear optical (LO) and NLO properties of the glasses highly depended on the introduction of heavy-metal ions. For gel glasses, the optical bandgap narrows with increasing radius of the heavy-metal ions and is associated with the heavy-metal ion-induced structural transformation of the glass. The NLO properties of both the binary and ternary glasses were extensively investigated using a well-developed Z-scan technology, and the possible NLO mechanisms were discussed. The results revealed that the NLO parameters, including the nonlinear absorption coefficient (β), nonlinear refraction index (n2), and third-order nonlinear susceptibility (χ(3)), all continuously increased with the increasing radius of the metal cation in the glasses, strongly suggesting that the optical nonlinearities can be easily controlled by adjusting the glasses’ compositions. The orders of magnitude of β, n2, and χ(3) were calculated at 10−12 m/W, 10−14cm2/W, and 10−13 electrostatic units (esu), respectively, which are comparable to those of recently reported glasses. Depending on the energy gap (Eg) value, the nonlinear absorption (NLA) can be attributed to two- or three-photon absorption. Furthermore, for the investigated glasses, the figure of merit (FOM) > 1. Our work provides an effective composition-tuning strategy for drastically improving third-order NLO properties, and these sol-gel-derived transparent glasses are suitable for use in ultrafast NLO-limiting applications.