Crystal structure and photoluminescence tuning of novel single-phase Ca8ZnLu(PO4)7:Eu2+,Mn2+ phosphors for near-UV converted white light-emitting diodes

Abstract

The discovery of novel single-phase and emission-tunable phosphors based on the strategy of Eu²⁺–Mn²⁺ energy transfer (ET) is a topic of ongoing interest due to the potential applications of near-ultraviolet (n-UV) converted white light-emitting diodes (WLEDs). Herein, we developed a brand-new Eu²⁺/Mn²⁺-codoped Ca₈ZnLu(PO₄)₇ (CZLP) phosphor and investigated its structural and luminescence properties in more detail for the purpose of verifying its single-phase and emission-tunability character. The crystal structure of CZLP and the preferential site occupations of the Eu²⁺ and Mn²⁺ dopants were identified and confirmed in the framework of the β-Ca₃(PO₄)₂-type structure by combined simultaneous application of the Rietveld refinement and first-principles calculations. Moreover, the CZLP:Eu²⁺,Mn²⁺ phosphors under an excitation of 360 nm exhibited color tuning from cyan (0.186, 0.292) to white (0.302, 0.273) with variation in the concentration ratio of Eu²⁺ to Mn²⁺. This tuning strategy to generate white light emission can be realized in our samples because of the Eu²⁺–Mn²⁺ ET process via predominant dipole–quadrupole interactions with a maximum ET efficiency of 65.55%. To finally evaluate the application potential of the as-synthesized phosphors, a WLED package was fabricated using a 360 nm n-UV chip and the optimal phosphor CZLP:0.03Eu²⁺,0.20Mn²⁺. The test results indicate that the obtained white-light device had a much better color rendering index (CRI ∼ 88.6) and correlated color temperature (CCT ∼ 4842 K) in comparison with the traditional combination of a blue light-emitting InGaN chip and Y₃Al₅O₁₂:Ce³⁺ phosphor.