Effective electron trap regulation in near-infrared persistent phosphor of ZnAl2O4:Cr3+ for round-the-clock plant lighting

Cr3+-doped phosphors are widely used in the near-infrared (NIR) phosphor-converted light-emitting diodes (pcLEDs) for plant growth lighting in the modern agriculture due to their excellent luminous efficiency and spectral tunability. However, the inevitable energy consumption and heat radiation issues force us to shift our focus to develop a novel plant lighting pattern of energy storage activated by sunlight and NIR afterglow illumination at night. Herein, a series of Zn1-xMgxAl2-2xGa2xO4:Cr3+ (ZMAGO:Cr3+) NIR persistent luminescence (PersL) phosphors, achieving a far-red emission at 675-775 nm upon 387 nm or 530 nm excitation is designed. The optimal ZMAGO:Cr3+ (x = 0.6) phosphor exhibits a 194-fold initial NIR afterglow intensity and PersL decay time last for more than 6 h. The enhancement of afterglow originates from the introduction of effective electron traps, which can be precisely controlled by changing the Mg2+/Ga3+ doping concentration. Meanwhile, by utilizing the photon transmission from SrAl2O4:Eu2+,Dy3+ green phosphor to ZMAGO:Cr3+ (x = 0.6) NIR phosphor, the prepared NIR coatings obtain 2.5 times enhanced PersL intensity and afterglow far more than 12 h by sunlight excitation, meeting the requirements of non-electrical excitation and round-the-clock plant lighting. The successful development of NIR coatings based on the ZMAGO:Cr3+ phosphor is expected to accelerate the exploitation of next generation of intelligent and energy friendly light sources for indoor agriculture.