ZnAl₂O₄:Cr3⁺ translucent ceramic phosphor with thermally stable far-red luminescence

Far-red-emitting ZnAl2O4:Cr3(+) phosphor ceramics were fabricated by the spark plasma sintering method. The photoluminescence characteristics, luminescence thermal stability, quantum yield (QY) has been investigated. The phosphor ceramic can be excited by the 350-450 nm near ultraviolet-blue light, with two emission peaks located at 687 nm and 699 nm, matching the active-state (P-FR) absorption band of plant photosensitive phytochrome. The blue (390-450 nm) and orange (550-580 nm) excitation bands of ZnAl2O4:Cr3(+) are due to the spin-allowed (4)A(2)-> T-4(1) and (4)A(2)-> T-4(2) transitions of Cr3+ ions. The phosphor ceramics are suitable for plant lighting in terms of acceptable QY (40%), high thermal conductivity (17.5 W.m(-1).K-1 at 25 degrees C), weak thermal quenching of luminescence (24% drop at 150 degrees C) and good PL (680-720 nm) features for plant growth.