Very stable and high-quantum-yield phosphor Na2BaSr(PO4)2:Eu2+ for plant growth LEDs

Abstract

Controlling the light environment for plant growth using phosphor-converted light-emitting diodes (pc-LEDs) is an important means to regulate growth rhythm and enhance yield, for which bluish-violet light is one of the essential and important spectral components, particularly for plant photosynthesis. To reduce cost and improve the spectral matching between the cultivation pc-LEDs and the plant response spectrum, phosphors with excellent spectrum resemblance (SR), thermal stability and quantum yield (QY) are necessary for practical applications. A bluish-violet-emitting (428 nm) phosphor, Na₂BaSr(PO₄)₂:Eu²⁺ (NBSP:Eu²⁺), with extremely high QY of about 92% was developed, which not only well matches the absorption spectrum of chlorophyll-a (SR_{chlorophyll-a} = 91.5%) in the blue region but also exhibits zero thermal quenching at the LED operating temperature (150 °C). The possible mechanism for its superior thermal stability was investigated and interpreted as the thermal ionization and recombination of Eu²⁺-5d with defect participation. Results indicated that NBSP:Eu²⁺ is a promising bluish-violet-emitting phosphor that possesses considerable potential application in plant growth LEDs.