Novel SrLaAlO4:Mn4+ deep-red emitting phosphors with excellent responsiveness to phytochrome PFR for plant cultivation LEDs: synthesis, photoluminescence properties, and thermal stability.

Herein, novel rare-earth-free Mn4+-doped SrLaAlO4 deep-red emitting phosphors were successfully synthesized via a traditional solid-state reaction method. The crystal structure and phase purity of the as-prepared samples were confirmed by XRD Rietveld refinement. Photoluminescence properties of SrLaAlO4:Mn4+ phosphors were examined in detail using photoluminescence spectra, decay lifetimes, temperature-dependent emission spectra and internal quantum efficiency measurements. The excitation spectrum obtained by monitoring at 730 nm contained two excitation bands centered at 364 and 520 nm within the range of 200-550 nm due to the Mn4+-O2- charge-transfer band and the 4A2g → 4T1g, 4T2g transitions of the Mn4+ ions. Under the 364 nm excitation, the SrLaAlO4:Mn4+ phosphors exhibited an intense deep-red emission band in 610-790 nm wavelength range peaking at 730 nm, which was assigned to the 2Eg → 4A2g transition of Mn4+ ions. The deep red emission showed excellent responsiveness to phytochrome PFR, revealing that the SrLaAlO4:0.4% Mn4+ phosphors possessed a possible application in deep-red light-emitting diodes (LEDs) for plant cultivation. The optimal doping concentration of Mn4+ ions was found to be 0.4 mol%. The critical distance R c for energy transfer among Mn4+ ions was determined to be 5.86 Šand the concentration quenching mechanism was confirmed to be the electric dipole-dipole interaction. In addition, the Commission International de I'Eclairage (CIE) colour coordinates of the SrLaAlO4:0.4% Mn4+ phosphors (0.734, 0.266) were located in the deep red region and the corresponding internal quantum efficiency was measured to be about 29%. The above results confirmed that the as-prepared SrLaAlO4:0.4% Mn4+ deep red emitting phosphors might be a potential candidate for plant cultivation LEDs.