Valence state control and third-order nonlinear optical properties of copper embedded in sodium borosilicate glass

The integrated and transparent sodium borosilicate glasses that contain copper exhibiting different colors, i.e. red, green and blue were synthesized by combining the sol–gel process and heat treatment in H2 gas. To reveal substantially the cause of different colors in the glass, X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) were systematically applied to investigate and determine the microstructure of the doped matter.