Crystal structure and photoluminescence of (La1-xCex)5Si3O12N

J. Alloys Compd., 2011, 509, 5, 2099. https://doi.org/10.1016/j.jallcom.2010.10.148

Oxonitridosilicate phosphors with compositions of (La1−xCex)5Si3O12N (x = 0–0.1) have been synthesized. The XRD analyses show that all the compounds are single polycrystalline La5Si3O12N phase. La atoms occupy two crystallographic sites in the structure. Two groups of photoluminescence spectra have been observed and can be ascribed to the excitation and emission of the two types of Ce3+ photoluminescence centers (Ce(1)3+ and Ce(2)3+) in the crystallographic sites of La(1) and La(2). The energy transfer between the two types of photoluminescence centers has been discussed. Schematic energy levels of Ce3+ ions at the two crystallographic sites are given. Luminescence concentration quenching occurs when Ce content is more than 3 mol%. The quenching temperature is evaluated to be about 406 K for the 3 mol% Ce content sample. This study shows these phosphors potential candidates for application in three-phosphor-converted white LEDs .

Synthesis, structure and luminescence of LaSi3N5:Ce3+ phosphor

J. Lumin., 2009, 129, 3,165. https://doi.org/10.1016/j.jlumin.2008.08.005

In this work, new LaSi3N5:Ce3+ phosphors have been synthesized by solid-state reaction. Rietveld refinement of the crystal structure of La1−xCexSi3N5 reveals that Ce atoms substituted for La atoms occupy 4a crystallographic positions. Broad emission and excitation bands observed were attributed to the transitions between the doublet ground state of the 4f1 configuration and the crystal field components of the 5d1 excited state. At 77 K, the centroid and crystal field splitting εcfs of the 5d levels of Ce3+ in LaSi3N5:Ce3+ compounds were valuated at 33.4×103 and 11.3×103 cm−1, respectively. The zero-phonon line and the Stokes shift were measured to be 26.0×103 and 5.0×103 cm−1, respectively .

Structure and luminescence of Ca2Si5N8:Eu2+ phosphor for warm white light-emitting diodes

Chin. Phys. B., 2009,18, 8, 3555. https://iopscience.iop.org/article/10.1088/1674-1056/18/8/070

We have synthesized Ca2Si5N8:Eu2+ phosphor through a solid-state reaction and investigated its structural and luminescent properties. Our Rietveld refinement of the crystal structure of Ca1.9Eu0.1Si5N8 reveals that Eu atoms substituting for Ca atoms occupy two crystallographic positions. Between 10 K and 300 K, Ca2Si5N8:Eu2+ phosphor shows a broad red emission band centred at ~1.97 eV–2.01 eV. The gravity centre of the excitation band is located at 3.0 eV–3.31 eV. The centroid shift of the 5d levels of Eu2+ is determined to be ~1.17 eV, and the red-shift of the lowest absorption band to be ~0.54 eV due to the crystal field splitting. We have analysed the temperature dependence of PL by using a configuration coordinate model. The Huang–Rhys parameter S = 6.0, the phonon energy hv = 52 m eV, and the Stokes shift ΔS = 0.57 eV are obtained. The emission intensity maximum occurring at ~200 K can be explained by a trapping effect. Both photoluminescence (PL) emission intensity and decay time decrease with temperature increasing beyond 200 K due to the non-radiative process .