A novel Na3La(PO4)2/LaPO4:Eu blue-red dual-emitting phosphor with high thermal stability for plant growth lighting

Abstract

A novel Na₃La₂(PO₄)₃:xEu (Na₃La(PO₄)₂/LaPO₄:xEu) blue-red dual-emission diphasic phosphor with high thermal stability is successfully synthesized by a high temperature solid state reaction. X-ray powder diffraction (XRD) analysis verified that the host of this dual emitting phosphor is a composite material composed of two crystals: Na₃La(PO₄)₂ and LaPO₄, which would realize the energy transfer between the two phases and then greatly enhance the luminescence properties. When compared with the single-phase phosphor Na₃La(PO₄)₂:xEu, the photoluminescence (PL) spectra of the as-synthesized diphasic phosphor showed significantly enhanced blue emission peaking at 422 nm of Eu²⁺ (5d-4f, a broadband at around 422 nm) and red emission peaking at 594 nm of Eu³⁺ (⁵D₀–⁷F_1,2, 594 and 621 nm) under UV excitation. Moreover, the phosphor exhibited a high thermal stability at 150 °C with up to 98.5% luminescence retention after Li⁺ co-doping, which should be attributed to the introduction of several defects. The emission spectra matched well with the photosynthetic action spectra (PAS) in plants, indicating that the Na₃La₂(PO₄)₃:xEu phosphor has a promising application in plant growth LED lighting.