Red phosphors A2GdNbO6: Mn4+ (A = Ca, Sr, Ba) for plant growth LEDs with Emerson enhancement effect

Mn4+-doped A2GdNbO6 (A = Ca, Sr, Ba) oxide-based red emitting phosphors were prepared via high-temperature solid-state reaction method. Under the irradiation of 365 nm light, all samples emit a broad red light in the range of 650–700 nm which matches well with the absorption band of photosynthetic pigments. Their emission spectra composed of zero-phonon line emissions at about 665 nm and a broad phonon sideband beyond 680 nm, which can induce plant Emerson Enhancement Effect to accelerate plant growth extremely. Furthermore, composition-dependent the quantum yield, thermal stability and zero-phonon line emissions intensity have been significantly enhanced and zero-phonon line shifted from 682 to ~665 nm with substituting Ca by Sr or Ba. The dependence of zero-phonon lines of Mn4+ on structural symmetry have also been investigated though density functional theory (DFT) calculation and structural symmetry analysis. LED devices have also been fabricated by combining 365 nm n-UV chip with 0.5%Mn4+-doped A2GdNbO6 (A = Ca, Sr, Ba).