Highly Efficient and Thermally Stable Eu2+-Doped Ca9Nd(PO₄)7 Phosphor for Near-Ultraviolet White-Emission LED Applications.

Various Eu²⁺-based Ca₉Nd(PO₄)₇ (CNP:xEu²⁺, with different x values) materials are prepared via facile solid-state reaction. Their crystal structures are investigated in detail by means of the Rietveld refinement. The structure of CNP:Eu²⁺ with a trigonal lattice is analogous to that of β-Ca₃(PO₄)₂. Therefore, Eu2+ ions tend to incorporate calcium sites in the host. All the obtained samples can be excited using near ultraviolet (nUV) light to present blue-green emission. An optimal dopant concentration is verified at x = 0.8 with a large critical interaction radius (11.21 Å). The mechanism of the concentration quenching effect is assigned to the multipole-multipole interaction. CNP:xEu²⁺ possesses a short decay lifetime of ∼60 μs and can endure severe working conditions thanks to its great thermal stability. The relative photoluminescence (PL) intensity of CNP:0.8Eu²⁺ can retain 84.75% of the pristine intensity measured at room temperature, and the relative intensity remains as high as 69.97% at 423 K. The CNP:Eu²⁺ phosphors also show great performance in the WLED demonstration. The correlated color temperature (CCT) of the prototype device is 3404 K, with an extremely high Ra (97.6). Therefore, CNP:xEu²⁺ could be regarded as a promising alternative to blue green phosphors in nUV chip-based WLED applications.