Structural and optical properties in Tm ³⁺ /Tm ³⁺ –Yb ³⁺ doped NaLuF ₄ glass‐ceramics

Abstract Transparent NaLuF ₄ glass‐ceramics (GCs) doped with Tm ³⁺ and Tm ³⁺ /Yb ³⁺ have been prepared by melting‐quenching followed by thermal treatment at temperatures near the glass transition temperature. The crystallization process has been studied using X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM). NaLuF ₄ nanocrystals (NCs) ranging 9–30 nm in size are the only crystalline phase, the crystal size increasing with the dopant concentration. Energy dispersive X‐ray (EDX) measurements confirm the Tm ³⁺ and Yb ³⁺ incorporation in the NCs. Optical characterization included the analysis of up‐conversion (UC) as well as the Near‐infrared (NIR) luminescence. NIR emission spectra of Tm ³⁺ and Yb ³⁺ in co‐doped samples confirmed an efficient energy transfer between both ions. No UC emissions are observed in Tm ³⁺ single‐doped glass and GCs. Yb ³⁺ incorporation favors the Tm ³⁺ ‐Tm ³⁺ UC processes resulting in Tm ³⁺ blue, yellowish‐red and NIR UC emissions after excitation at 975 nm. Blue UC emission is also observed in the codoped samples after Tm ³⁺ excitation at 791 nm. These effects were more evident for the GCs compared to the base glasses, confirming the RE ions incorporation in the NCs. As a result, these GCs can be used to tune the UC emission from NIR to blue by selective excitation.