Effectively realizing broadband spectral conversion of UV/visible to near-infrared emission in (Na,K)Mg(La,Gd)TeO6:Mn4+,Nd3+,Yb3+ materials for c-Si solar cells via efficient energy transfer

In this work, a series of (Na,K)Mg(La,Gd)TeO6:Mn4+,Nd3+,Yb3+ materials were prepared via a high-temperature solid-state reaction method. As reported before, certain Mn4+ singly doped samples present good red luminescence properties, showing emission bands at around 700 nm upon excitation with UV/n-UV/blue light. When Mn4+ and Nd3+ were co-doped into the same host, effective energy transfer from Mn4+ to Nd3+ ions was inferred from the spectral overlap of the Mn4+ emission and Nd3+ excitation bands. The variation of the emission bands upon 365 nm UV excitation with fixed Mn4+ concentration and varying Nd3+ concentration in phosphors can validate this energy transfer process from Mn4+ to Nd3+ ions. In addition, comparison of the excitation spectra monitored at the Nd3+ emission peaks to those monitored at the Mn4+ emission bands and the decrease of the Mn4+ decay times supplied more evidence for the energy transfer phenomenon from Mn4+ to Nd3+ ions in these Mn4+,Nd3+ co-doped samples. Since the energy transfer from Nd3+ to Yb3+ ions has been well reported before, we co-doped Yb3+ in our Mn4+,Nd3+ co-doped samples to show that Nd3+ can be a bridging ion to regulate the energy transfer from Mn4+ to Yb3+ ions for the first time, which was confirmed from the analysis of the excitation spectra and decay times. This can be considered as a novel method to enhance the energy transfer from Mn4+ to Yb3+ ions. Based on the energy transfer from Mn4+ to Nd3+ and then to Yb3+, UV/visible luminescence can be effectively converted into near-infrared emission, allowing a better spectral response for c-Si solar cells, which suggests a possible enhancement of the conversion efficiency of such c-Si solar cells.