Synthesis, structure and luminescence of LaSi3N5:Ce3+ phosphor

Journal of Luminescence, 2009,3,129(3):165-168

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

CHINESE PHYSICS B., 2009,18(8),3555-3562

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.