Dual‐mode photoluminescence of Ba ₂ GdF ₇ : Yb ³⁺ , Er ³⁺ , Eu ³⁺ spheroidal nanoparticles for optical anticounterfeiting

Abstract A series of Yb 3+ , Er 3+ and Eu 3+ doped Ba 2 GdF 7 spheroidal nanoparticles are prepared by hydrothermal procedure. Upconversion (UC) and downconversion (DC) dual‐mode luminescence are obtained in Yb 3+ ‐Er 3+ ‐Eu 3+ tri‐doped Ba 2 GdF 7 and energy transfer processes are investigated in detail. Under 980 nm near‐infrared (NIR) excitation, the UC photoluminescence of Ba 2 GdF 7 : Yb 3+ , Er 3+ , Eu 3+ is dominated by intense green (521& 540 nm, 2 H 11/2 / 4 S 3/2 → 4 I 15/2 ) and red emission (651 nm, 4 F 9/2 → 4 I 15/2 ) from Er 3+ due to efficient energy transfer (ET) of Yb 3+ → Er 3+ , the continuous ET of Yb 3+ → Er 3+ → Eu 3+ leads to weak red UC emission of Eu 3+ (591 nm, 5 D 0 → 7 F 1 ). Under 273 nm ultraviolet (UV) excitation, characteristic 525, 555, 591, 619, 650, and 699 nm emissions of Eu 3+ from 5 D 2 → 7 F 3 , 5 D 1 → 7 F J (J = 1, 2) and 5 D 0 → 7 F J (J = 1, 2, 3, 4) transitions are obtained through predominant Gd 3+ → Eu 3+ ET process. Tunable DC emission color from yellow to orange‐red are achieved by adjusting Eu 3+ content in Ba 2 GdF 7 : Yb 3+ , Er 3+ , Eu 3+ . The concentration optimized Ba 2 GdF 7 : 25 mol% Yb 3+ , 6 mol% Er 3+ , 15 mol% Eu 3+ nanophosphor exhibits green and orange‐red light under NIR and UV excitation, respectively, indicating the application prospect in optical anticounterfeiting and information encryption.