Yellow to Orange-red Tunable Broadband-emitting (Ca, Sr)O:Ce3+ Solid Solution Phosphors for Plant Growth Application

Abstract

The application of light conversion materials provides a new approach to improving plant photosynthetic efficiency and promoting plant growth. We have prepared (Ca, Sr)O:Ce³⁺ phosphors and observed two unique phenomena within them: 1) the red shift of Ce³⁺ emission from 568 nm (CaO:Ce³⁺) to 600 nm (Ca_0.2Sr_0.8O:Ce³⁺) while the excitation remains unchanged (470 nm); 2) self-luminescence from the (Ca, Sr)O host lattice. Structural refinement data prove that the emission red shift is due to the expansion of the lattice resulting in a more relaxed coordination environment, while an idea of looser excitation state curve was consistent with a phenomenon “invariance of excitation energy”. Evidence from the fluorescence lifetime ultimately confirms that the self-luminescence of the host lattice should be attributed to color centers within the lattice. Considering the red light ratio and emission intensity, Ca_0.7Sr_0.3O:Ce³⁺ is the most suitable phosphor. In the Chlorella growth experiment, the experimental group using the Ca_0.7Sr_0.3O:Ce³⁺ light conversion film achieved a final OD value 21% higher than the blank control group. All the above results indicate that the sunlight conversion films prepared from Ca_0.7Sr_0.3O:Ce³⁺ phosphors have great potential in promoting plant growth.