The fluorescence intensity ratio (FIR) technique has emerged as a pivotal approach in non-contact optical thermometry, offering substantial application potential. In this study, Y 3 Al 5 O 12 (YAG) phosphors co-activated with Ce 3+ and Cr 3+ ions were successfully synthesized through a high-temperature solid-state reaction method. Spectroscopic analysis revealed efficient energy transfer between the dopant ions, manifesting as distinct luminescence intensity variations compared to their single-doped counterparts. Under 450 nm excitation, the system demonstrates prominently yellow-green emission from Ce 3+ ions and well-resolved red emission from Cr 3+ ions, ensuring excellent spectral discrimination. Capitalizing on the differential thermal response between the two luminescent centers, the developed system achieves remarkable temperature sensing performance. The FIR method yields a maximum relative sensitivity of 0.845 % K −1 , maintaining sensitivity above 0.6 % K −1 throughout the 340–580 K range, coupled with exceptional temperature resolution below 0.03 K. Furthermore, we have engineered a novel FIR thermometry system incorporating 3D-printed spectral modules and fiber-optic phosphor encapsulation. The integrated system demonstrates superior sensing capabilities, reaching sensitivity values of 1.23 % K −1 in Cr 3+ lifetime mode and 4.64 % K −1 in FIR mode. These results indicate that Ce/Cr co-doped YAG has exceptional potential in multimodal optical thermometry applications.
The mid-infrared focal plane array (FPA) imager has developed over recent decades to become multifunctional, powerful, reliable, miniaturized, and cost-effective. However, the complexity of the refrigerated packaging process (such as dewar flask) and traditional fabrication technology (such as flip-chip) continues to contribute significantly to the high cost of industrial production. Here, a simple, low-cost, and effective type of uncooled mid-infrared FPA imager is reported through the monolithic integration of mid-infrared Pb 1-x Sn x Se nanocrystals (NCs) PIN heterojunction (PbS/Pb 1-x Sn x Se/ZnO) photodetectors and glass-based readout integrated circuits (ROICs). Sn-doping in PbSe NCs not only weakens the internal photocarrier-phonon coupling to reduce thermal noise but also optimizes the energy band structure of the heterojunction to enhance mid-infrared performance. Finally, the PbS/Pb 0.86 Sn 0.14 Se/ZnO heterojunction photodetector demonstrates a dark current (2.7 x 10 −7 A mm −2 at −0.5 V), a detectivity of 7.46 × 10 9 Jones at a peak wavelength of 4.25 µm, air stability (retaining 96.7% performance at 300 K for 360 days) and the corresponding uncooled mid-infrared FPA (64 × 64 pixels) achieves excellent thermal sensitivity of 133 mK. These results underscore the substantial potential applications of mid-infrared FPA based on the heterojunction, including spectral imaging, gas leak detection, and chemical reagent identification.
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