Novel Sr ₄ GaNbO ₈ :Dy ³⁺ , Mn ⁴⁺ Materials Toward Excellent Dual‐Mode Fluorescent Temperature Sensing, Optical Anti‐Counterfeiting, Information Encryption, and Latent Fingerprint Recognition Applications

Herein, a novel kind of multi‐functional phosphors Sr 4 GaNbO 8 (SGNO):Dy 3+ , Mn 4+ were synthesized using a high‐temperature solid‐state reaction approach. Under different UV excitations, simultaneous characteristic emissions of Dy 3+ around 490 and 578 nm, and Mn 4+ around 712 nm were exhibited, realizing tunable luminescence from yellow to red, based on the energy transfer between Mn 4+ and Dy 3+ in the co‐doped phosphors. By utilizing the fluorescence intensity ratio (FIR) technique, maximum relative sensitivities (S r ) and absolute sensitivity (S a ) were achieved to be 14.12% K −1 @298 K and 2.33 K −1 @473K, respectively, for representative SGNO:0.04Dy 3+ , 0.005Mn 4+ , which were much higher than most reported results. Remarkably, we innovatively proposed a fluorescence lifetime ratio (FLR) prototype approach based on the distinct temperature‐dependent lifetime behaviors for Dy 3+ and Mn 4+ , achieving maximal S r and S a values of 34.08% K −1 @298 K and 5.22 K −1 @393 K for the SGNO:0.04Dy 3+ , 0.005Mn 4+ sample, which are both over twice higher than those obtained using FIR technology above, demonstrating that this FLR method is of high potential in designing fluorescent thermometers with higher sensitivity. In addition, the phosphor exhibited clear fluorescent fingerprint imaging and excitation‐ and temperature‐dependent luminescence, enabling applications in optical sensing, information encryption, and anti‐counterfeiting.