Lattice engineering and data analysis as a dual-strategy to push cryogenic thermal sensing in single-band Eu3+ ratiometric thermometry

Cutting-edge technologies, such as quantum computing and superconducting magnets, rely on cryogenic temperatures, a domain in which luminescence thermometry (LT) offers a viable route for sensing. Here, we extend single-band ratiometric (SBR) thermometry by combining ground- and excited-state absorption (GSA and ESA, respectively) with a dual strategy that integrates Al 3+ -induced lattice distortions with multiparametric analysis. For that, the (Gd,Y) 2 O 3 :Eu 3+ (0–9 at%) phosphors and their 3 at% Al 3+ co-doped analogues were studied. Structural analysis revealed that Al 3+ contracts the lattice and stiffens RE─O bonds. Under GSA, Eu 3+ emission decreases with heating, while under ESA ( 5 D 0,1 ← 7 F 1 ) the opposite behavior is observed, enabling SBR through two intensity ratios, LIR 1 and LIR 2 , defined as the intensity ratio between the 5 D 0 → 7 F 2 band under ESA (531 nm, 5 D 1 ← 7 F 1 , or 586 nm, 5 D 0 ← 7 F 1 ) and GSA at 464 nm ( 5 D 2 ← 7 F 0 ), for both 7Eu and 7EuAl phosphors. The co-doped sample exhibited higher relative sensitivity (S r ) than the single-doped analogue near 80 K (2.52% K −1 vs 2.08% K −1 , δT < 0.15 K), an outcome associated with enhanced cross-relaxation due to lattice contraction. Merging LIR 1 and LIR 2 into a unified parameter via non-negative matrix factorization (NMF) yielded a five-fold enhancement in S r . This result demonstrates that cryogenic temperature sensing can be advanced to new performance thresholds by coupling materials engineering with data-driven analysis.