Correlations between structural properties of Nb2O5NaPO3Na2B4O7 glasses and non-linear optical activities

Information about the origin of the optical non-linear response in transparent glasses can be gained from a detailed structure investigation using Raman and X-ray absorption spectroscopies. The effects resulting from the introduction of niobium oxide in the sodium borophosphate matrix of composition 0.95NaPO30.05Na2B4O7 are described. For small niobium concentrations, the formation of distorted NbO6 octahedra is observed. The increase of niobium concentration allows the progressive linking of corner-shared and less distorted octahedra. The correlative evolution of the measured third order susceptibilities χ(3) is analyzed on the basis of the bond orbital theory. A good agreement between experimental and calculated χ(3) is obtained as long as the NbO6 entities are isolated from each other, but the clustering of these entities increases the non-linear response, χ(3).