Self-crystallized novel transparent Na₅Yb₉F₃₂: Er³⁺ glass-ceramics for optical thermometry and spectral conversion

Novel self-crystallized transparent Na₅Yb₉F₃₂: Er³⁺ glass-ceramics (GCs) were successfully elaborated through high temperature melt-quenching route for the first time. X-ray diffraction (XRD), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and photoluminescence emission spectra confirmed that the Na₅Yb₉F₃₂ nanocrystals (NCs) were well-formed without any additional phase. In addition, X-ray photoelectron spectroscopy (XPS) was studied for investigating valence states of elements in the Na₅Yb₉F₃₂: Er³⁺ GCs and it was suggesting that Er³⁺ ions was doped into the Na₅Yb₉F₃₂: Er³⁺ GCs. Interestingly, the XRD patterns and TEM images demonstrate that the Na₅Yb₉F₃₂ NCs have already formed during melt-quenching process without any further heat treatment. Due to improved crystallinity, reduced surface-to-volume ratio and more Er³⁺ incorporation into NCs after further heat treatment, both up-conversion (UC) and down-conversion (DC) show enhanced luminescence intensity after heat treatment. The emission color of Na₅Yb₉F₃₂ GCs changed under different ultraviolet excitation wavelength was addressed and interpreted by photoluminescence. Furthermore, via the fluorescence intensity ratio (FIR), the temperature-dependent green UC emissions of Na₅Yb₉F₃₂: Er³⁺ GCs were studied under 980 nm laser excitation. Provided with broad operating temperature range (300–773 K), large energy gap of thermal coupled energy levels (835 cm⁻¹) and high sensitivity (1.33% K⁻¹ at 300 K), the Na₅Yb₉F₃₂: Er³⁺ GCs may have potential application in temperature senor. - Highlights: • Novel transparent glass-ceramics Na₅Yb₉F₃₂: Er³⁺ was successfully fabricated. • The glass-ceramics have already formed during melt-quenching process. • The structural and morphology properties of the samples were analyzed. • Both up-conversion and down-conversion are greatly enhanced after heat treatment. • Temperature dependent of GC680 indicates their good optical thermometry property.