Energy transfer in Cr and Nd co-doped Si-B-Na-Al-Ca-Zr-O glasses

Cr and Nd co-doped glasses are potential gain media for solar pumped lasers (SPLs). Tanabe-Sugano analysis shows that Cr doped Si-B-Na-Al-Ca-Zr-O (SBNACZ) glass contains a mixture of Cr³⁺ with octahedral coordination and Cr⁶⁺with unknown coordination. The crystal field parameters for Cr³⁺ were Dq = 1574 cm⁻¹, B = 792.2 cm⁻¹, C = 3005 cm⁻¹ and Dq/B = 1.99, indicating a low covalency of Cr-O bonds. We compared the quantum efficiency (QE) of Nd and Cr co-doped SBNACZ glass with Nd doped SBNACZ glass to determine the Cr³⁺→Nd³⁺ transfer QE. The Cr₂O₃ content was fixed at 0.1 mol.% and the Nd₂O₃ content was varied between 0.1 and 1 mol.%. A maximum transfer QE of 20% was obtained at 0.5 mol.% Nd₂O₃. Cr³⁺→Nd³⁺ energy transfer is dominated by the coulombic interaction mechanism. The clustering of Nd³⁺ was a limiting factor for increasing the transfer QE with higher Nd³⁺ concentrations.