Color-tunable photoluminescence and persistent luminescence in a single LiYGeO₄:Tb³⁺ phosphor

Abstract

Persistent luminescence (PerL) phosphors have been widely applied in many advanced applications in the field of emergency lighting, safety signage, and ornaments. Recently, the PerL phosphors based on germanates have attracted great attention owing to their excellent PerL performance. However, the design and development of excellent germanates-based PerL materials with full spectral emissions remain challenging due to the lack of color-tunable PerL, especially in the blue and green regions (400-600 nm). Herein, we develop a new type of Tb3+-activated LiYGeO4 PerL phosphor with real-time adjusting the photoluminescence (PL) and PerL color, which can be effectively excited by a 254 UV light. Both blue and green PerL are realized simultaneously in a single phosphor. When LiYGeO4:Tb3+ doped with lower concentrations of Tb3+ ions, phosphors emit blue PL and PerL. With increasing Tb3+ concentration, the PL and PerL colors of LiYGeO4:Tb3+ PerL phosphor are gradually regulated from blue to green. Besides, LiYGeO4:Tb3+ exhibits temperature-dependent luminescence property, whose PL and PerL colors can also be successively widely tuned by various temperature. This stable and tunable color in real-time PL and PerL property promote the as-designed LiYGeO4:Tb3+ phosphor to have potential applications in advanced anti-counterfeiting and display devices.

Tunable and enhanced mechanoluminescence in LiYGeO4:Tb3+via Bi3+ → Tb3+ energy transfer

“…30 The other weak peaks located at 328 nm ( 7 F 6 → 5 D 0 ), 335 nm ( 7 F 6 → 5 D 1 ), 343 nm ( 7 F 6 → 5 L 8 ) and 352 nm ( 7 F 6 → 5 G 4 ) originate from the 4f → 4f transitions of Tb 3+ ions. 29 Under 254 nm excitation, the PL spectra of Li 0.997 YGeO 4 :0.5% Bi 3+ , x Tb 3+ ( x = 0.3%, 0.5%, 1.0%, 6.0%, 20.0% and 30.0%) show a peak at 355 nm, which can be attributed to the 3 P 1 → 1 S 0 of Bi 3+ ions. 30…”

“…When the Tb 3+ concentration is beyond 1.0%, the cross-relaxation (CR) process of 5 D 3 + 7 F 6 → 5 D 4 + 7 F 0 may occur, which results in luminescence quenching of the emission from the 5 D 3 excited state. 29 Consequently, a very wide range of emission colors can be continuously tuned by different Tb 3+ concentrations.…”

“…30 The other weak peaks located at 328 nm ( 7 F 6 -5 D 0 ), 335 nm ( 7 F 6 -5 D 1 ), 343 nm ( 7 F 6 -5 L 8 ) and 352 nm ( 7 F 6 -5 G 4 ) originate from the 4f -4f transitions of Tb 3+ ions. 29 Under 254 nm excitation, the PL spectra of Li 0.997 YGeO 4 :0.5% Bi 3+ ,xTb 3+ (x = 0.3%, 0.5%, 1.0%, 6.0%, 20.0% and 30.0%) show a peak at 355 nm, which can be attributed to the 3 P 1 -1 S 0 of Bi 3+ ions. 30 The peaks at 379, 415, 437, 459, 485, 559, 583, and 621 nm correspond to the transitions of 5 D 3 and 5 D 4 excited state levels to 7 F J ( J = 3-6) ground state levels, respectively, which is clearly shown in Fig.…”

“…6c and d exhibit two strong bands peaking at 348.9 and 379.5 K. And there is also a weak peak at 459 K, which is ascribed to Bi. 29,31,38 Using the empirical equation: 19…”

“…28 Zhang et al reported that the LiYGeO 4 :Bi 3+ phosphor has super-long PersL far more than 72 h in the UVA region peaking at 350 nm, which originates from a large number of traps created by the loss of Li + ions. 29 A mass of deep traps makes a great contribution to realizing ML, and we also have realized the UVA ML in LiYGeO 4 :Bi 3+ previously, hence LiYGeO 4 is finally chosen as the host material. 30 In this work, LiYGeO 4 :Tb 3+ ,Bi 3+ phosphors are successfully synthesized by the traditional solid-state reaction method in air.…”