Er³⁺-activated Ba₂V₂O₇ upconversion nanosheets for dual-mode temperature sensing

So far, there has been substantial research on non-contact luminescence thermometry approaches that rely on luminescence intensity ratio (LIR) technology. However, there is limited availability of phosphors doped with Er³⁺ ions that exhibit on-par luminescence and high sensitivity. In this work, samples of Ba₂V₂O₇:Er³⁺ were synthesized using a sol-gel method aided by citric acid. The luminescence properties of these samples, including upconversion and down-shifting, were investigated using both ultraviolet and 980 nm laser stimulation. When subjected to ultraviolet (UV) light, the sample exhibits a distinct broadband emission that appears pale green. This emission is a distinguishing property of the sample and is attributed to the presence of V₂O₇^2- ions. Upon being stimulated by a 980 nm laser, the sample exhibits standard green up-conversion Er³⁺ emission bands. Concurrently, an assessment was conducted on the phosphor's ability to measure temperature by analysing the LIR between the thermally coupled ²H_11/2, ⁴S_3/2 energy levels (TCELs) and the non-thermally coupled ²H_11/2, ⁴F_9/2 energy levels (NTCELs) of the Er³⁺ ion. The corresponding highest sensitivity of temperature for TCELs and NTCELs can position Ba₂V₂O₇:Er³⁺ nanosheets as a capable option for materials utilized in temperature-sensing applications.