Bi and Yb Codoped Cs₂Ag_0.6Na_0.4InCl₆ Microcrystals: Visible to Near-Infrared Fluorescence for Thermometry

The optical and thermometric properties of bismuth (Bi) and ytterbium (Yb) codoped double perovskite Cs 2 Ag 0.6 Na 0.4 InCl 6 microcrystals (MCs) are investigated, which possess high photoluminescence quantum yield and stable broadband spectra from visible to near-infrared (NIR) region. Thermal quenching and dynamic properties are shown using temperature-dependent steady-state photoluminescence (PL) and time-resolved PL (TRPL) techniques, which reveal the transition mechanism from self-trapped excitons (STEs) to Yb dopants. Taking advantage of the diverse thermal quenching of distinct PL between STEs and Yb 3+ emissions, an optical thermometer based on the fluorescence intensity ratio is designed in the visible and NIR region, which can provide a self-referenced temperature with high sensitivity. The maximum absolute and relative sensor sensitivities are 0.113 K –1 and 1.66% K –1, respectively. These characteristics all demonstrate that Bi/Yb codoped Cs 2 Ag 0.6 Na 0.4 InCl 6 MCs can be excellent and novel luminescent materials for non-contact temperature measurement.