Yb3+/Ln3+/Cr3+ (Ln = Er, Ho) doped transparent glass ceramics: crystallization, Ln3+ sensitized Cr3+ upconversion emission and multi-modal temperature sensing

Abstract

Currently, efficient photon anti-Stokes (upconversion) luminescence is mostly limited to lanthanide (Ln³⁺) doped materials. There are a few reports on upconversion behaviors of transition-metal ions, whose (Stokes) emissions are known to be tunable by changing the crystal fields of the hosts. Herein, Yb/Ln/Cr (Ln = Er, Ho) tri-doped glass ceramics were fabricated by a melt-quenching route and subsequent glass crystallization, where Cr³⁺ dopants were evidenced to be incorporated into the precipitated LiGa₅O₈ nanocrystals and Ln³⁺ ions remained in the glass matrix. An intense Cr³⁺ upconversion luminescence assigned to the ²E → ⁴A₂ transition was observed upon 980 nm laser excitation via energy transfer from Yb³⁺ sensitizers to Er³⁺ activators/bridging-centers and finally to Cr³⁺ emitting centers. Importantly, the investigated glass ceramics presented temperature-dependent upconversion fluorescence intensity ratios for Er^{3+ 2}H_11/2/⁴S_3/2 thermally coupled states as well as Cr³⁺/Ln³⁺ non-thermally coupled states and temperature-sensitive upconversion decays of Cr^{3+ 2}E/⁴A₂ thermally coupled states, enabling their promising applications in self-calibrated multi-modal temperature sensing.