Gadolinium vacancy induced photoluminescence enhancement of Cr3+-doped Gd3-xGa5O12 near-infrared garnet phosphors for plant cultivation

Abstract

Near-infrared (NIR) phosphors have increased in popularity owing to their unique optical properties and have been widely used in phosphor converted light emitting diodes (pc-LEDs) for plant cultivation in recent years. However, their low luminous intensity and poor thermal stability restrict their application in high-powder LEDs. In this study, a series of Gd3-xGa5O12:Cr3+ phosphors was successfully prepared by reducing the Gd3+ content to introduce gadolinium vacancies into the lattice. The structural stability of Gd3-xGa5O12:Cr3+ was confirmed using X ray diffraction and transmission electron microscopy. The emission intensity was improved by introducing Gd3+ vacancies into the lattice and the emission intensity of the optimized Gd2.9Ga5O12:Cr3+ was 135% higher than that of Gd3Ga5O12:Cr3+. At high temperatures, the emission spectra were broadened and shifted toward the NIR direction and maintained 84.6% of the luminescence intensity at 423 K compared with that at room temperature. The bandgap structures of Gd3Ga5O12 with and without vacancies were determined via density functional theory to explain the improvement in luminescence. Finally, an NIR-LED device was fabricated and applied to the cultivation of dragon fruit plants. The results showed that the growth rate and fruit set rate of dragon fruit were greatly improved by irradiation with NIR light source. This technique of creating vacancies in the lattice provides a new approach to enhance the luminescence properties of NIR phosphors for plant cultivation.