Understanding the cyan-emitting phosphor RbNa(Li3SiO4)2: Eu2+ by providing Rb ion vacancies

In rare earth ions doped luminescent materials, the luminescence properties of rare earth ions occupying different sites are often different. Phosphors Rb1-xNa(Li3SiO4)2: xEu2+ with bimodal cyan emission (472 nm and 523 nm) were synthesized by providing Rb ion vacancies. As a comparison, green phosphors RbNa1-y(Li3SiO4)2: yEu2+ were synthesized by providing Na ion vacancies. Based on the experiment and the formula proposed by Van Uitert, it is found that the emission peak of Eu2+ occupying Na+ sites is 523 nm, while the emission peak of 472 nm is caused by Eu2+ occupying Rb+ sites. Furthermore, according to the Density Functional Theory (DFT) calculation, the formation energy of Eu2+ substituted Na+ sites (ΔEf=−4.64 eV) is lower than the formation energy of Eu2+ substituted Rb+ sites (ΔEf=−3.94 eV), indicating that Eu2+ doped in RbNa(Li3SiO4)2 is easier to enter Na+ sites. This conclusion is consistent with the spectral information obtained in the experiment. By combining bimodal cyan emitting phosphor Rb0.9Na(Li3SiO4)2: 0.1Eu2+ with red phosphor CaAlSiN3: Eu2+ and a 430 nm LED chip, prepared wLEDs exhibit a high color rendering index (CRI, Ra = 88.9) and a suitable correlation color temperature (CCT) (CCT = 3714 K). The research results indicate that the bimodal cyan emitting phosphor Rb0.9Na(Li3SiO4)2: 0.1Eu2+ obtained through vacancy engineering has important application potential in the field of wLEDs illumination.