Correlations between structural properties of Nb2O5-NaPO3-Na2B4O7 glasses and non-linear optical activities
Résumé
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 0.95NaPO30.05Na2B4O7 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).