Multifunctional Titanium‐Rich Gadolinium Titanate Nanophosphors: A Leap toward Advanced Optical Thermometry and Flexible NIR LED‐Based Phototherapy

Abstract Upconversion (UC) materials are rapidly emerging as promising next‐generation platforms for advanced optical technologies. Herein, multifunctional integration of TiO ₂ ‐Gd ₂ Ti ₂ O ₇ (TGT):Er ³⁺ /Yb ³⁺ UC nanophosphors via a facile wet‐chemical technique is reported. As‐prepared hollow brick‐like particles, initially in a carbonate hydrate phase, transformed into nanoparticles with a cubic pyrochlore structure upon calcination. These nanophosphors display a dominant far‐red emission alongside a moderate green emission under 980 nm laser excitation. Among different compositions, the TGT:1Er ³⁺ /10Yb ³⁺ nanophosphors have shown excellent temperature sensing capabilities, achieving maximum absolute and relative sensitivities of 0.0048 K ⁻¹ at 353 K and 0.78% K ⁻¹ at 298 K for thermally coupled (TC) states, and 0.0017 K ⁻¹ at 433 K and 1.35% K ⁻¹ at 298 K for non‐thermally coupled (N‐TC) states. The study reveals that laser‐induced heating has a negligible effect on N‐TC‐based sensing, whereas low pump powers are preferable for TC‐based sensing. The multifunctionality of these nanophosphors is further established by fabricating a flexible phosphor film integrated into an NIR LED for horticultural lighting and phototherapy, and a far‐red emitting UC ink for anti‐counterfeiting. These findings underscore the potential of TiO ₂ ‐rich Gd ₂ Ti ₂ O ₇ :Er ³⁺ /Yb ³⁺ nanophosphors as a versatile platform for advanced sensing, photonics, and security applications.