Novel SrLaAlO 4 :Mn 4+ deep-red emitting phosphors with excellent responsiveness to phytochrome P FR for plant cultivation LEDs: synthesis, photoluminescence properties, and thermal stability.

Herein, novel rare-earth-free Mn ⁴⁺ -doped SrLaAlO ₄ 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 SrLaAlO ₄ :Mn ⁴⁺ 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 Mn ⁴⁺ -O ^2- charge-transfer band and the ⁴ A _2g → ⁴ T _1g , ⁴ T _2g transitions of the Mn ⁴⁺ ions. Under the 364 nm excitation, the SrLaAlO ₄ :Mn ⁴⁺ phosphors exhibited an intense deep-red emission band in 610-790 nm wavelength range peaking at 730 nm, which was assigned to the ² E _g → ⁴ A _2g transition of Mn ⁴⁺ ions. The deep red emission showed excellent responsiveness to phytochrome P _FR , revealing that the SrLaAlO ₄ :0.4% Mn ⁴⁺ phosphors possessed a possible application in deep-red light-emitting diodes (LEDs) for plant cultivation. The optimal doping concentration of Mn ⁴⁺ ions was found to be 0.4 mol%. The critical distance R _c for energy transfer among Mn ⁴⁺ ions was determined to be 5.86 Å and 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 SrLaAlO ₄ :0.4% Mn ⁴⁺ 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 SrLaAlO ₄ :0.4% Mn ⁴⁺ deep red emitting phosphors might be a potential candidate for plant cultivation LEDs.
Competing Interests: There are no conflicts to declare.
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