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 Ca3Si3−xO3+xN4−2x: Eu2+ 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 Ca3Si3−xO3+xN4−2x: Eu2+ phosphor can serve as the green phosphor for n-UV w-LEDs, with a tunable spectrum by controlling the crystal structure and morphology.
Highlights
505.2 to 540.8 nm, which is attributed to the crystal field splitting
The phase composition of as-synthesized phosphors was identified by X-ray powder diffraction (XRD)
When the x value diverges the optimum one (x = 1), lattice is gradually distorted and symmetry of local environment decreased. This lattice distortion is conducive to generating a broader emission spectrum, but leads to an increase in ΔSS, causing a bigger thermal quenching
Summary
505.2 to 540.8 nm, which is attributed to the crystal field splitting. The enhanced crystal field splitting broadens the excitation spectrum, making it possible to serve as the phosphor for near ultraviolet (n-UV) LEDs. Solid solution is the easiest and most cost-efficient way, especially for nitride, because structural diversity and different O/N ratio of (oxy) nitride greatly influence the 5d energy level of rare earth ions, which contributes to tunability of luminescence spectrum[10,11] Based on these three strategies, a variety of phosphors have been developed, including oxides, oxyfluorides, sulfide, phosphate and (oxy) nitrides. (Oxy) nitride phosphors have received significant attention in recent years due to their encouraging luminescent properties, such as excitability by blue light, high conversion efficiency, the possibility of full color emission, as well as their low thermal quenching and high chemical stability. Several reports on photoluminescence properties of Eu2+ or Ce3+ doped Ca3Si2O4N2 have been published in recent years, research on this potential host as a phosphor is still at a primary stage[28,29,30]
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