A Highly Efficient Eu2+ Excited Phosphor with Luminescence Tunable in Visible Range and Its Applications for Plant Growth

A series of RbxK2−xCaPO4F:Eu2+ phosphors are synthesized using a high‐temperature solid‐phase method. An increase in the Rb+ concentration leads to the Eu2+‐excited phosphor emission spectra being shifted from red to cyan. Interestingly, the excitation spectrum does not exhibit any variations, which indicates the possibility of mixing the red (Rb0.2K1.8CaPO4F:Eu2+) and cyan (Rb2CaPO4F:Eu2+) phosphors for plant growth. This luminescence tuning is attributed to the substitution of K+ with Rb+, which produces an inferior crystal‐field splitting that increases the energy at the lowest 5d level, and enhances the rigidity of the crystal structure, which results in a gradual decrease in the Stokes shift and a consequent blue shift in the emission spectrum. Time‐resolved photoluminescence emission spectroscopy further confirms the occurrence of broadband emission owing to the occupation of multiple sites by Eu2+. Light‐emitting devices appropriate for plant growth are fabricated by mixing the two phosphors with a 380‐nm UV chip, and a light‐conversion film is prepared using the red phosphor and PDMS glue. The Chlorella‐based plant growth experiment reveals that the growth rate of Chlorella is 12.2% higher than that of the blank group, indicating the favorable effect of the light‐conversion film on plant growth.