L-Ta 2 O 5 :Er 3+ /Yb 3+ upconversion phosphors were synthesized by employing the molten salts method with B 2 O 3 as solvent. The optimal doping concentrations of Er 3+ and Yb 3+ are 0.2 and 2.5 mol%, respectively. The green upconversion luminescence (UCL) integral intensity of the acid-pickling sample reached 40% of β-NaYF 4 :Er 3+ /Yb 3+ under 980 nm laser excitation. Er 3+ /Yb 3+ may take the sites of Ta 5+ and insert into the interlayers of L-Ta 2 O 5 . Using the luminescence intensity ratio (LIR) technique, the relative temperature sensitivity was obtained to be 0.95 %K −1 at 303 K. L-Ta 2 O 5 :Er 3+ /Yb 3+ with outstanding pure green UCL intensity and high-temperature sensitivity can be applied to luminescence display and temperature sensing.
By using the molten salt synthesis with B 2 O 3 flux and adjusting the doping concentration of Y 3+ , the intergrowth of the YTa 7 O 19 phase in L-Ta 2 O 5 is achieved. This structure enhances the pure green upconversion luminescence (UCL) intensity, which is because the YTa 7 O 19 phase isolates the distribution of Er 3+ /Yb 3+ in the 2D layer, localizing the energy transfer from Yb 3+ to Er 3+ and reducing the loss during the energy transfer process. By adjusting the concentration of Er 3+ /Yb 3+ and the holding temperature, the green UCL integral intensity of the optimal sample is 1.09 times that of β-NaYF 4 :Er 3+ /Yb 3+ . The intergrowth of the YTa 7 O 19 phase in L-Ta 2 O 5 is demonstrated by high-resolution transmission electron microscopy (HRTEM) and comparing bandgap values, and the structure and properties cannot be obtained by solid phase sintering. Using the luminescence intensity ratio (LIR) technology, the absolute temperature sensitivity (S A ) and relative temperature sensitivity (S R ) were 0.01359 K −1 and 0.01001 K −1 , respectively. The phosphor-converted 980 nm LEDs based on samples are fabricated, the CIE color coordinate can reach (0.20, 0.76), which exceeds NTSC standard. This indicates that this material can be used for temperature sensing and luminescence display applications.
Er3+/Yb3+/Sr2+-doped L-Ta2O5 upconversion phosphors were synthesized using the molten salt method with B2O3 as the solvent. High-resolution transmission electron microscopy (HRTEM) results showed that Er3+/Yb3+/Sr2+ underwent intercalated intergrowth in L-Ta2O5. This structure facilitates energy transfer from Yb3+ to Er3+, resulting in outstanding pure green upconversion luminescence (UCL) intensity. The green UCL integrated intensity of L-Ta2O5:Er3+/Yb3+/Sr2+ was 1.53 and 3.14 times greater than that of β-NaYF4:Er3+/Yb3+ and the optimal NaY(WO4)2:Er3+/Yb3+ samples, respectively. The absolute and relative temperature sensitivity reached 1.383% and 0.992% K−1, respectively. The shift rate of the peak centroids reached 0.273 nm GPa−1 under high pressure. With its excellent performance, L-Ta2O5:Er3+/Yb3+/Sr2+ can be used in the fields of UCL display, temperature and pressure sensing.
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