Pure green and pure red upconversion luminescence due to different distributions of Er3+/Yb3+ in tantalate

The Rb₄Ta₆O₁₇:Er³⁺/Yb³⁺ upconversion luminescence (UCL) powders were prepared by using ion-exchange intercalation growth method. When the concentration of Er³⁺ is 10 mol% and that of Yb³⁺ is 30 mol%, the pure green UCL intensity is the highest under 980 nm laser excitation. This pure green UCL is attributed to the 2D layered distribution of Er³⁺/Yb³⁺. The Rb₄Ta₆O₁₇:0.1Er³⁺/0.3Yb³⁺ sample was subjected to heat treatment at different temperatures, and the Rb₄Ta₆O₁₇ structure transformed into the Rb₄Ta₁₁O₃₀ structure above 800 °C. The Rb₄Ta₁₁O₃₀:Er³⁺/Yb³⁺ shows pure red UCL under 980 nm laser excitation. The energy transfer (ET) from Yb³⁺ to Er³⁺ occurs in the four layers space of Rb₄Ta₁₁O₃₀, which increases the space of energy transfer and cross relaxation with leading to pure red UCL emission. Based on the luminescence intensity ratio (LIR) technology, the relative temperature sensitivity can reach 1.527 % K⁻¹. This experiment demonstrated that by adjusting the spatial distribution of Er³⁺/Yb³⁺ in the tantalate, pure green or pure red UCL can be achieved. Rb₄Ta₆O₁₇:Er³⁺/Yb³⁺ and Rb₄Ta₁₁O₃₀:Er³⁺/Yb³⁺ can be used for pure color luminescence display and temperature sensing.