Efficient stabilization of Cu⁺ ions in phosphate glasses via reduction of Cu²⁺ by Sn²⁺ during ambient atmosphere melting

Glasses containing substantial amounts of well-dispersed luminescent Cu⁺ ions are attractive materials for applications in solid-state lighting, photonic waveguides, and solar cells. Thus far, coming across a simple yet effective method for the preparation of such has remained elusive given the instability of Cu⁺ relative to Cu²⁺, especially for syntheses carried out under the oxidizing air atmosphere. In this work, high concentrations of monovalent copper ions are shown to be successfully incorporated in a high-solubility phosphate glass matrix by a simple melt-quench method. The traditional Cu²⁺ spectrophotometric analysis commonly utilized for liquid solutions is proposed herein for the solid-state material to estimate the reduction efficiency of Cu²⁺ during the material preparation process. Reproducibly, the use of relatively large quantities of copper(II) oxide with equal amounts of reducing agent tin(II) oxide (up to 20 mol%), together with the use of sucrose to assist as antioxidant during melting in air atmosphere, yields high-reduction efficiencies estimated at 98 %. Along with the optical absorption analysis, photoluminescence spectroscopy is employed in evaluating the emission properties of the glasses in connection to the Cu⁺ ions. Further, solid-state ³¹P nuclear magnetic resonance spectroscopy reveals the structural features of the glasses that support the remarkable stabilization of the Cu⁺ ions.