Effect of heavy-doping Eu3+ and charge compensation on crystalline phase and luminescence properties of K2CaP2O7 phosphors emitting orange-red light

A series of K₂Ca_1-xP₂O₇:xEu³⁺ phosphors were prepared by a high-temperature solid-state reaction method. The crystal structure was analyzed by X-ray diffraction (XRD). Fluorescence spectra, decay curves, and color coordinates were investigated. Under excitation at 393 nm, the strongest emission peak was located at 590 nm, corresponding to the ⁵D₀→⁷F₁ transition of Eu³⁺, and the sub-strongest one was located at 612 nm which belongs to the ⁵D₀→⁷F₂ transition of Eu³⁺. XRD results show that the patterns doped with a small amount of Eu³⁺ were fitted well with the standard card of K₂CaP₂O₇, while the pattern with the doping of high concentration Eu³⁺ (heavy-doping) indicated the co-existence of K₂CaP₂O₇ and EuPO₄ phase which leads to luminescent intensity of phosphors enhance remarkablely. The concentration quenching mechanism was explained through dipole-dipole interaction. Different doping amounts of Eu³⁺ and charge compensators will affect the symmetry of the host lattice, thereby affecting the emission intensity ratio of orange and red light. The color coordinates of K₂Ca_0.49P₂O₇:0.51Eu³⁺ and K₂Ca_0.33P₂O₇:0.67Eu³⁺, 0.1Na⁺ phosphor were near the red region, which was close to commercial red-emitting phosphors Y₂O₃:Eu³⁺ and standard red light, respectively.

Graphical abstract

A series of K₂CaP₂O₇ phosphors emitting orange-red light with different concentrations of Eu³⁺ doping and alkali metal ions co-doping were synthesized via a high-temperature solid-state method, and their structure and luminescent properties were characterized. A new strategy for adjusting the light color parameters of K₂CaP₂O₇ phosphors has been constructed.