Ca(Mg_0.8Al_0.2)(Si_1.8Al_0.2)O₆:Ce³⁺,Tb³⁺ Phosphors: Structure Control, Density-Functional Theory Calculation, and Luminescence Property for pc-wLED Application

Abstract

A modified structure Ca(Mg_0.8Al_0.2)(Si_1.8Al_0.2)O₆ (denoted as CMASO) from the evolution of CaMgSi₂O₆ (denoted as CMSO) codoped with Ce³⁺ and Tb³⁺ ions was designed successfully by solid reaction method for application in phosphor-converted white-light-emitting diode (pc-wLED). The Rietveld refinement of these two structures verified the changes derived from the replacement of some of the Mg²⁺ and Si⁴⁺ ions by Al³⁺ ions. The band gaps were calculated by density-functional theory (DFT) calculation method to verify the change of Al³⁺ ions replacing further, and the diffuse reflectance spectra (DRS) proved the veracity of the calculation result. The phosphors CMASO:Ce³⁺ showed blue emission excited by a wider excitation wavelength from 280 nm to 370 nm. The change of structure lead to the absorbable range broaden and the emission peak shifted to longer wavelength, compared with CMSO:Ce³⁺, although the amount of emitting center was the same. The reason for these phenomena was discussed in detail. The codoped phosphors CMASO:Ce³⁺,Tb³⁺ exhibited different emission colors from blue to green as the concentration of Tb³⁺ ions increased. Combined with commercial red phosphor CaAlSiN₃:Eu²⁺ and ultraviolet LED (UV-LED) chips, the selected appropriate samples achieved white emission. The correlated color temperature (CCT) was 6137 K and the color rendering index (Ra) was 80.5, indicating that they could act as potential phosphors for possible applications in pc-wLED.