Single-Entity Nanophosphor for Efficient Dual-Mode Luminescence by Tridoped Ln 3 + Ions in a CaWO ₄ Host for Anticounterfeiting and Temperature-Sensing Applications

Multifunctional rare-earth-doped luminescent nanomaterials capable of simultaneous spectral conversion and sensing are of significant interest for advanced photonic applications. Herein, we report the synthesis of efficient Eu3+-codoped CaWO4:Er3+, Yb3+ nanophosphors via a polyol method and demonstrate their excitation-dependent multicolor emission, optical thermometry, and anticounterfeiting functionality. Under UV excitation, intense Eu3+-dominated red emission is achieved with an optimal Eu3+ concentration of 4 atom %, while higher doping leads to concentration quenching. Near-infrared (NIR) excitation at 980 nm produces an efficient Er3+-based green upconversion emission, which is maximized in Eu3+-free sample, and its green emission intensity decreases upon Eu3+ incorporation. The energy transfer efficiency and mechanism from the Er3+ excited states to the Eu3+ excited states are discussed. Lifetime measurements corroborate the emission behavior, yielding a maximum lifetime for Eu3+ at 4 atom % Eu3+ (∼550 μs and ∼581 μs under 269 and 393 nm excitation, respectively), and a lifetime of ∼97 μs for Er3+ green emission under 980 nm excitation. Using thermally coupled Er3+ energy levels, optical thermometry achieves a relative sensitivity of 1.22% K–1 at 303 K, an absolute sensitivity of 1.15% K–1 at 393 K, and a temperature resolution of ∼0.4 K near room temperature. The observed dual-mode red and green emissions under UV and NIR excitation, respectively, underscore the potential of these nanophosphors for optical thermometry and anticounterfeiting-related applications.