Introduction The energy transfer between lanthanide ions (Ln3+) and transition metal ions (Cr3+) typically leads to luminescence attenuation, which hinders their application in temperature measurement. However, this issue can be effectively addressed by synthesizing polyphase glass-ceramics that separate the Ln3+ and Cr3+ into different nano-crystals.In this study, we designed polyhedral glass-ceramics (40SiO2-20Al2O3-15LiF-10Ga2O3-0.1TmF3-0.1ErF3-0.05Cr2O3-1YbF3-0.5SnO) doped with Ln3+/Cr3+ (Ln3+=Er3+/Tm3+/Yb3+). The up-conversion spectra of Tm3+ and Er3+ in the temperature range of 313–573 K, as well as the temperature-dependent properties of the emission intensity ratio of 2E and 4T2 and fluorescence lifetime decay of Cr3+ were systematically investigated. The results demonstrate that Ln3+/Cr3+-doped polyphase glass-ceramics exhibit excellent performance as a four-mode fluorescence temperature measurement material.
Methods Ln3+/Cr3+-doped glass samples were prepared using melt quenching technology, where the raw materials were melted in a lifting furnace at 1 500 ℃ for 1 h. The sample was then poured onto a preheated copper plate to 300 ℃ and shaped by pressing it with another copper plate. Subsequently, the sample was annealed in a Muffle furnace at 450 ℃ for 6 h to obtain precursor glass (PG). Finally, the PG sample underwent heat treatment at 780 ℃ for 2 h to produce glass-ceramics (GC780).X-ray diffraction apparatus was employed to measure the XRD spectra of these samples. FS-5 fluorescence spectrometer was used to measure various spectra including up-conversion and down-conversion spectra at room temperature, power-dependent up-conversion spectra, temperature-dependent up-conversion and down-conversion spectra, as well as temperature-dependent fluorescence lifetime decay curves. Transmission electron microscopy techniques such as selective electron diffraction and high-power transmission electron microscopy were utilized to examine GC780 samples.
Results and discussion The diffraction peaks observed in the XRD pattern of GC780 exhibit excellent agreement with the standard cards of γ-Ga2O3 and β-YF3 respectively, indicating the successful synthesis of polyphase glass-ceramics containing γ-Ga2O3 and β-YF3 grains. The excitation and emission spectra of Cr3+ as well as the up-conversion spectra of Er3+ and Tm3+ indicate no energy transfer between Cr3+ and Er3+ or Tm3+. In the variable temperature up-conversion emission spectra of GC780 sample within a temperature range of 313 to 573 K, the emission peak intensity ratio (FIR) I522/I543 and I694/I474，which change with temperature, were selected for temperature detection. As the temperature increases from 313 K to 573 K, there is a decrease in relative sensitive (SR) for I522/I543 with increasing temperature, reaching a maximum value of 1.03%·K–1 at 313 K. On the other hand, SR for I694/I474 initially increases and then decreases with rising temperature, peaking at a maximum value of 1.45%·K–1 at 473 K. In the down-conversion temperature-changing spectra (303–543?K) of Cr3+ excited at 397 nm, the intensity of the luminescence peaks at 615 nm and 720 nm is used to detect the temperature dependence of FIR(I615/I720). When the temperature is from 303 K to 543 K, SR gradually decreases with increasing temperature, and the maximum value of 1.74%·K–1 appears at 303 K. The relative sensitivity is 0.51%·K–1 at 496 K when Cr3+ down-conversion attenuation curve is used to measure temperature dependence.
Conclusions Polyphase glass-ceramics doped with β-YF3 and ?-Ga2O3 nano-crystals in Ln3+/Cr3+ (Ln3+=Er3+/Tm3+/Yb3+) have been successfully synthesized by melt quenching method in this work. The up-conversion spectra of GC780 were measured in the temperature range of 313–573 K. The maximum relative sensitivities were 1.03%·K–1 and 1.45%·K–1, respectively, by selecting I522/I543 and I694/I474 intensity ratios. The 2E→4A2 and 4T2→4A2 emission2 peaks of Cr3+ were used for temperature detection, and the maximum relative sensitivity was 1.74%·K–1 at 303 K. In addition, the Cr3+ down-conversion attenuation curve is used to measure the temperature dependence, and the maximum relative sensitivity is 0.51%·K–1 at 496 K. The Ln3+/Cr3+ (Ln3+=Er3+/Tm3+/Yb3+) co-doped β-YF3 and ?-Ga2O3 nano-crystals polyphase glass-ceramic is thus indicated to be a highly promising competitive four-mode self-calibration temperature measurement material.