Photoluminescence properties of rare earth doped α-Si3N4

The photoluminescence properties of Eu2+, Ce3+ and Tb3+ doped α-Si3N4 have been studied and a possible structural model has been proposed on the basis of the Rietveld refinement of X-ray powder diffraction data. Nearly single phase rare earth doped α-Si3N4 was synthesized by a solid state reaction at 1600 °C in N2–H2 atmosphere starting from amorphous Si3N4 and rare earth oxides or nitrides. Because of small crystal field splitting of the 5d levels, the excitation and emission bands of Eu2+ and Ce3+ are positioned at higher energies as isolated ions in comparison with that in Ca-α-Sialon. Both Eu2+- and Ce3+-doped α-Si3N4 show blue band emission peaking at about 470 and 450 nm, respectively, under UV excitation. α-Si3N4:Tb3+ exhibits dominant green line emission mainly arising from 5D4→7FJ (J=6–3) with weak 5D3→7FJ (J=6–3) transitions of Tb3+ when excited by UV light. The thermal stability of α-Si3N4:Eu2+ is comparable with that of Ca-α-Sialon:Eu2+ and is much better than that of α-Si3N4:Ce3+.