Discovery of novel solid solution Ca ₃Si _{3− x} O _{3+ x} N _{4−2 x} : Eu ²⁺ phosphors: structural evolution and photoluminescence tuning

Abstract

Discovery of novel phosphors is one of the main issues for improving the color rendering index (CRI) and correlated color temperature (CCT) of white light-emitting diodes (w-LEDs). This study mainly presents a systematic research on the synthesis, crystal structure variation and photoluminescence tuning of novel (oxy)nitride solid solution Ca ₃Si _{3− x} O _{3+ x} N _{4−2 x} : Eu ²⁺ phosphors. XRD refinements show that lattice distortion occurs when x value diverges the optimum one ( x = 1). The lattice distortion causes a widening of emission spectrum and an increase of Stokes shift (ΔSS), which leads to a bigger thermal quenching. With decrease of x value, the emission spectrum shows an obvious red-shift from 505.2 to 540.8 nm, which is attributed to the crystal field splitting. The enhanced crystal field splitting also broadens the excitation spectrum, making it possible to serve as the phosphor for near ultraviolet (n-UV) LEDs. A 3-phosphor-conversion w-LED lamp was fabricated with the as-prepared phosphor, which exhibits high CRI (Ra = 85.29) and suitable CCT (4903.35 K). All these results indicate that the Ca ₃Si _{3− x} O _{3+ x} N _{4−2 x} : Eu ²⁺ phosphor can serve as the green phosphor for n-UV w-LEDs, with a tunable spectrum by controlling the crystal structure and morphology.