Bi3+/Ln3+-Codoped Boroaluminate Phosphors with Tunable Multicolor Emission for Multidimensional Luminescence Readout and UV-Shielding

Abstract Combining lattice regulation of crystal-field-sensitive Bi3+ emission with Bi3+ → Ln3+ sensitization provides two complementary pathways for tuning the luminescence of single-host phosphors. Herein, Bi3+-activated Sr6Lu1-yYyAl(BO3)6 solid solutions and Bi3+/Ln3+-codoped Sr6LuAl(BO3)6 (SLAB; Ln = Eu, Dy, Sm, and Tb) phosphors were synthesized by a high-temperature solid-state reaction. SLAB:Bi3+ exhibited broadband blue-violet emission centered at 419 nm under 325 nm excitation. Isovalent Y3+ substitution for Lu3+ regulated the local environment of Bi3+ and enhanced the integrated emission intensity by approximately sixfold under 365 nm excitation, with internal and external quantum efficiencies (IQE and EQE) reaching 87.2 and 31.7%, respectively. The lifetime-derived efficiency of Bi3+ → Eu3+ energy transfer reached a maximum of 85.8% and enabled continuous color tuning from blue-violet to orange-red by adjusting the Eu3+ concentration and excitation wavelength. Bi3+ → Ln3+ sensitization was further demonstrated for Dy3+, Sm3+, and Tb3+, producing purple, purplish-red, and green emissions, respectively. Taking advantage of their strong UV absorption, the phosphors were incorporated into flexible films for a proof-of-concept evaluation of UV shielding. The tunable multicolor emissions were further used to fabricate multicolor security labels and demonstrate binary optical encryption. Differential thermal quenching of Bi3+ and Sm3+ emissions enabled ratiometric thermometry over 298–573 K, with maximum absolute and relative sensitivities of 6.55 × 10–2 K–1 and 1.07% K–1, respectively. These findings demonstrate the potential of single-host boroaluminate phosphors for multidimensional luminescence readout, optical thermometry, and UV-shielding applications.