A promising yellow phosphor of Ce3+/Li+ doped CaSiN(2-2δ/3)Oδ for pc-LEDs

Single-phased orthorhombic nitridosilicate CaSiN2 powders were prepared at 1550 °C in a N2/H2 (6%) atmosphere by solid-state reaction using Ca3N2 and Si3N4 as the starting materials. The crystal structure refinements were carried out by the Rietveld method based on the X-ray and neutron powder diffraction data collected at 297 K, respectively. The CaSiN2 phase crystallizes in an orthorhombic unit cell with the space group Pbca (No. 61) and cell parameters a = 5.1334(3) Å, b = 10.3090(5) Å, c = 14.5756(5) Å, Z = 16 (XRD data). Instead of the ideal formula CaSiN2, small amounts of oxygen could be detected in the samples. The O/N composition of orthorhombic CaSiN2-2δ/3Oδ was analyzed by EDX and Rietveld refinement on the neutron powder diffraction data. SAED and HREM characterizations of the crystallites were conducted before the EDX analysis in order to select proper crystallites and exclude other minor second phases of (oxo)nitridosilicates such as cubic CaSiN2 and monoclinic CaSi2O2N2. The luminescence measurements indicate that Ce(3+)/Li(+) co-doped CaSiN2-2δ/3Oδ emits a typical shouldered yellow band peaking at 530 nm (FWHM ∼ 120 nm), which originates from the 5d → 4f transition of Ce(3+). The emission band shifts to longer wavelengths with an increment of Ce(3+) concentration. The strong excitation band appears in the range of 350-470 nm, which is very favorable for the applications in near-UV and blue phosphor-converted light-emitting diodes (pc-LEDs).