Luminescent properties of the Sr8−xBaxMgY(PO4)7:Eu2+ solid solution

Abstract

Photoluminescence generated by substituting rare-earth ions on multiple crystallographically independent cation sites within a crystalline host material is one of the most common approaches for creating a full-spectrum phosphor-converted white light-emitting diode (pc-wLED). In this work, a series of complex orthophosphates with the composition (Sr_8−xBa_x)_0.99Eu_0.08MgY(PO₄)₇ (x = 0, 1, 2, 3) were synthesized via high-temperature solid-state synthesis. These materials possess five potential substitution sites achieving broadband (5905 cm⁻¹) yellow photoluminescence through multi-site substitution showing a violet-excited photoluminescent quantum yield of nearly 50%. Developing such an efficient broad emission spectrum is crucial for enhancing the color rendering ability of pc-wLEDs. Varying the Sr²⁺ to Ba²⁺ shifts the emission color from green-yellow to yellow under violet excitation (λ_ex = 400 nm) while influencing the full-width-at-half-maximum (fwhm). Temperature-dependent photoluminescence measurements indicate that phosphor has good thermal stability with T₅₀, the temperature at which the emission intensity is half of the low-temperature intensity, at 420 K and stable chromaticity coordinates, further supporting that the (Sr_8−xBa_x)_0.99Eu_0.08MgY(PO₄)₇ series are promising candidates for LED white lighting. Constructing a prototype pc-wLEDs device using (Sr₇Ba)_0.99Eu_0.08MgY(PO₄)₇, the highest quantum yield phosphor, produced a functional daylight bulb with a color rendering index (CRI) of 90.