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.