A terbium-sensitized Eu3+-activated deep-red-emitting phosphor for plant growth LED application

Abstract

Traditional Eu3+-activated inorganic phosphors are habitually used for general lighting and display because they generally emit either intense orange (5D0-7F1) or red (5D0-7F2) light whose wavelength is shorter than 630 nm. However, less known nor focused is that Eu3+ at sites with specific symmetry can intensify its 5D0-7F4 transition, enabling Eu3+ itself to emit deep red light (>700 nm) even stronger than the above orange and red ones. Herein, a novel Eu3+-activated phosphor, Ca2TbSn2Al3O12:Eu3+, is developed from the garnet structure. Differing from other Eu3+-activated phosphors, the 5D0-7F4 transition of Eu3+ in the host is dominant and the orange, red and deep red emissions are balanced. Such special features of Eu3+ luminescence mainly meet the need of phytochromes (PFR and PR) in plants. Additionally, bridge style energy transfer from the host composition element Tb3+ to the activator Eu3+ can be observed. It is found the Tb3+-Eu3+ energy transfer here takes through the mechanism of dipole-dipole interaction and the simulation on decay curve of Eu3+ upon Tb3+ excitation, for the first time, confirms the existence of terbium bridge energy transfer. For the Ca2Tb0.60Sn2Al3O12:0.40Eu3+, the energy transfer efficiency is as high as 94.4% and the emission color is totally red. Thermal quenching studies reveal that the emission intensity of the phosphor at 425 K sustains 80% of its initial intensity at room temperature. By fabricating the phosphor with a 380 nm LED chip, a plant-growth LED device can be obtained.