Novel Mn5+-activated Ba2TiO4 phosphor emitting in the second near-infrared biological window

In recent years, second near-infrared window emitting phosphors have gained widespread research interest due to their excellent tissue penetration and high imaging accuracy. In this work, a new type of Ba₂Ti_1-xMn_xO_4+x/2 (0.02 ≤ x ≤ 0.10) phosphors were successfully prepared by high-temperature solid-phase method and their potential in luminescence thermometry is evaluated. PL and PLE spectral analysis prove that the optimal Mn doping concentration is x = 0.03. The as-synthesized phosphors exhibit a broad excitation band of 550–1000 nm and a narrow emission band of 1170–1220 nm. The electronic structures of the original Ba₂TiO₄ and Mn-doped Ba₂TiO₄ were calculated and analyzed using the DFT + U method, which facilitates a better understanding of the impact of Mn doping on the luminescent properties of Ba₂TiO₄. The luminescence decay lifetime is measured to be 101.44 μs at room temperature, which is a giant enhancement compared to conventional nanosecond lifetime phosphor, indicating a progress in imaging accuracy. In addition, the as-synthesized phosphors maintain over 75 % of the maximum luminescence intensity within the physiological temperature range. The potential applications in luminescence temperature measurement were also analyzed by the LIR ratio method, and the relative sensitivity could reach 2.31 %K⁻¹ at 283 K, which is a relatively high value in the second near-infrared window. Therefore, the as-synthesized Ba₂Ti_1-xMn_xO_4+x/2 (0.02 ≤ x ≤ 0.10) phosphors demonstrate great potential in NIR applications such as biological imaging and luminescent thermometry.