Highly sensitive high-temperature optical thermometry enabled by dual-emission design exploiting opposite thermal...

Non-contact optical thermometry is essential for temperature diagnostics in aerodynamic and propulsion environments where conventional contact sensors fail. However, the widely used fluorescence intensity ratio (FIR) technique becomes less reliable at elevated temperatures, as the thermal population distribution between coupled levels causes the relative sensitivity (S_r) to decrease rapidly with the square of temperature. To overcome this constraint, a dual-emission approach based on the summation of opposite monochromatic sensitivities was developed using YVO₄: Eu³⁺ & CaMoO₄: Er³⁺ composite system. Under a common 380 nm excitation, Eu³⁺ and Er³⁺ emissions exhibit opposite and monotonic temperature dependences, yielding enhanced overall sensitivity in the higher-temperature region through their combined response. Experimental results reveal a maximum Sr of 1.85%·K^-1 at 633 K and a temperature uncertainty (ΔT) below 1 K even at 743 K. This method overcomes the ΔE/ k_BT² limitation of thermally coupled level-based thermometry and provides a reliable approach for non-contact, high performance surface temperature diagnostics in wind tunnel.