Synthesis, luminescence properties and potential applications for plant growth: A novel Mn4+-activated SrLa2Al2O7 phosphor with far-red emission

The far-red light with peak wavelength around 730 nm plays an important role in plant growth. However, there are few emission spectra of Mn4+-doped oxide phosphors that could match with the absorption spectrum of phytochromes Pfr. In this study, a series of Mn4+-activated SrLa2Al2O7 phosphors was successfully synthesized by the method of high-temperature solid-state reaction. The structure of Mn4+-activated SrLa2Al2O7 was characterized and photoluminescent properties, thermal stability, luminescence lifetime, and internal quantum efficiency (IQE) were measured. The SrLa2Al2O7 phase structure belongs to I4/mmm (139) space group with a tetragonal system. Under 365 nm excitation, far-red emission spectra of SrLa2Al2O7:Mn4+ phosphors range from 650 nm to 800 nm with a peak at 731 nm, which matches well with the absorption band of the phytochrome Pfr. The crystal field strength Dq/B of Mn4+ ions in SrLa2Al2O7 matrix is 2.79. The optical band gaps are 5.04 eV for SrLa2Al2O7. The integrated emission intensity of SrLa2Al1.994O7:0.006Mn4+ phosphors at 373 K remains 43% of that at room temperature, and the luminescence lifetime is 1.99 ms. Finally, the as-prepared SrLa2Al1.994O7:0.006Mn4+ phosphors were mounted on a 365 nm NUV chip to fabricate far-red emitting LED devices. The observed emission spectra were confirmed to match well with the spectra of phytochrome Pfr, which implies that SrLa2Al2O7:Mn4+ phosphors have potential applications in the field of plant growth illumination.