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Orange‑red‑emitting ­CaTi4(PO4)6:Eu3+ phosphor for white LEDs: synthesis and luminescence properties Renping Cao1 · Wenhua Shao1 · Yanshu Zhao1 · Ting Chen1 · Hui Ao1 · Siling Guo1 · Pan Liu1 · Ting Fan2 Received: 11 January 2020 / Accepted: 5 March 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract CaTi4(PO4)6:xEu3+ phosphors are successfully synthesized under air condition by high-temperature solid-state method. The crystal structure, morphology, energy spectrum, atomic percentage, elemental mapping, and luminescence properties are investigated, respectively. Monitored at 594 nm, the excitation spectral bands of C ­ aTi4(PO4)6:Eu3+ phosphor in the range 2− 3+ of 210–550 nm are assigned to the ­O –Eu charge transfer band (CTB) and the 7F0 → 5H3, 5L7, 5L6, 5D1, 5D2, 5D3, and 5 D4 transitions of E ­ u3+ ion. With excitation at 394 nm, C ­ aTi4(PO4)6:Eu3+ phosphor emits orange-red light with the chromaticity coordinates (0.548, 452), and the emission spectral bands in the region from 575 to 720 nm are attributed to the 5 D0 → 7F1, 7F2, 7F3, and 7F4 transitions of ­Eu3+ ion. The optimal doping concentration of ­Eu3+ ion is ~ 8 mol%. The lifetime of ­CaTi4(PO4)6:Eu3+ phosphors decreases from 1.87 to 0.97 ms with increasing E ­ u3+ concentrations from 1 to 10 mol%. 3+ ­CaTi4(PO4)6:Eu phosphor has a good thermal stability. The experimental results indicate that C ­ aTi4(PO4)6:Eu3+ phosphor has an application prospect in white light-emitting diodes (LEDs) based on the near ultraviolet (~ 394 nm) LED chip. Keywords  Phosphors · CaTi4(PO4)6 · Luminescence properties · Eu3+ ion · Orange-red emission

1 Introduction Because the conventional lighting sources (e.g., incandescent light bulb and fluorescent lamp) have many disadvantages (e.g., the short lifetime, high energy consumption, low efficiency, and environmental pollution), the solid-state lightings as the fourth-generation light source are known as the most promising lighting to replace them [1–4]. In particular, white light-emitting diodes (WLEDs) as solid-state lighting are attracting much attention because of the high efficiency, small volume, long lifetime, energy saving, and environmental friendliness [5–7]. At present, the phosphorconverted WLEDs (pc-WLEDs) are known as the fourthgeneration green lighting source and widely applied in many fields (e.g., the lighting display, transportation, electronic * Renping Cao [email protected] * Ting Fan [email protected] 1



College of Mathematics and Physics, Jinggangshan University, Ji’an 343009, China



School of Materials Science and Energy Engineering, Foshan University, Foshan 528000, China

2

products, and medical devices) because they have excellent absorption, narrow emission, good thermal/chemical stability, high luminous efficiency [8–11]. There are two main preparation approaches for pc-WLEDs. The first method is made by the combination of blue-emitting GaN chips and yellow-emitting ­Y3Al5O12:Ce3+ (YAG:Ce3+) phosphors, whose application is affected by the low color rendering index (CRI)