Luminescence Properties of Ca₁₉Ce(PO₄)₁₄:A (A = Eu³⁺/Tb³⁺/Mn²⁺) Phosphors with Abundant Colors: Abnormal Coexistence of Ce^4+/3+-Eu³⁺ and Energy Transfer of Ce³⁺ → Tb³⁺/Mn²⁺ and Tb³⁺-Mn²

A series of Eu³⁺/Tb³⁺/Mn²⁺-ion-doped Ca₁₉Ce(PO₄)₁₄ (CCPO) phosphors have been prepared via the conventional high-temperature solid-state reaction process. Under UV radiation, the CCPO host presents a broad blue emission band from Ce³⁺ ions, which are generated during the preparation process because of the formation of deficiency. The Eu³⁺-doped CCPO phosphors can exhibit magenta to red-orange emission as a result of the abnormal coexistence of Ce³⁺/Ce⁴⁺/Eu³⁺ and the metal-metal charge-transfer (MMCT) effect between Ce³⁺ and Eu³⁺. When Tb³⁺/Mn²⁺ are doped into the hosts, the samples excited with 300 nm UV light present multicolor emissions due to energy transfer (ET) from the host (Ce³⁺) to the activators with increasing activator concentrations. The emitting colors of CCPO:Tb³⁺ phosphors can be tuned from blue to green, and the CCPO:Mn²⁺ phosphors can emit red light. The ET mechanism from the host (Ce³⁺) to Tb³⁺/Mn²⁺ is demonstrated to be a dipole-quadrapole interaction for Ce³⁺ → Tb³⁺ and an exchange interaction for Ce³⁺ → Mn²⁺ in CCPO:Tb³⁺/Mn²⁺. Abundant emission colors containing white emission were obtained in the Tb³⁺- and Mn²⁺-codoped CCPO phosphors through control of the levels of doped Tb³⁺ and Mn²⁺ ions. The white-emitted CCPO:Tb³⁺/Mn²⁺ phosphor exhibited excellent thermal stability. The photoluminescence properties have shown that these materials might have potential for UV-pumped white-light-emitting diodes.