Anomalous tunable visible to near infrared emission in the Mn2+-doped spinel MgGa2O4 and room-temperature upconversion in the Mn2+ and Yb3+-codoped spinel

Abstract

In contrast to common visible emission, an anomalous near-infrared (NIR) emission band at 790 nm has been demonstrated in the spinel structure MgGa₂O₄:Mn²⁺ with heavy Mn²⁺ doping. Tunable single-band visible to visible-NIR and single-band NIR emission are easily realised upon tuning the doping concentration of Mn²⁺. Careful investigation of the crystal structure, fluorescence lifetime and excitation & emission spectra indicates that the NIR emission might be ascribed to the ⁶A₁(⁶S)⁴T₁(⁴G) → ⁶A₁(⁶S)⁶A₁(⁶S) transitions of Mn²⁺–Mn²⁺ dimers. When some Yb³⁺ ions are codoped into the spinel MgGa₂O₄:Mn²⁺, room temperature visible upconversion (UC) emission is realised upon excitation with a 976 nm laser diode. The temperature-dependent UC emission properties as well as the related UC mechanism have been investigated. Understanding the nature of the Mn²⁺ Stokes and UC emissions is the key to developing advanced photonic devices with improved properties and manufacturability for engineering applications.