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▼ [14a-411-3] Luminescence property and local structure of phase pure La3Si6.5Al1.5N9.5O5.5:Ce phosphor
Keywords:sialon, phosphor, white LED
Rare-earth ions doped M-Si-Al-O-N (M = metal) phosphors have been extensively investigated, owing to their large flexibility in tuning the photoluminescence spectra, high conversion efficiency, small thermal quenching and high chemical stability. However, highly efficient deep blue emitting phosphor is still lacking. The crystal structure of Al-containing La N(ew) phase La3Si6.5Al1.5N9.5O5.5 has been reported by Grins et al in 2001,[1] while no report on photoluminescence of rare-earth ions doped La3Si6.5Al1.5N9.5O5.5 phosphors can be found so far. Additionally, the local Si and Al coordination environments are not clear, due to lack of a phase pure sample.
In this work, we have obtained phase pure non-doped sample and blue-emitting La3Si6.5Al1.5N9.5O5.5:Ce phosphor with solid-state reaction method for the first time. The excitation spectrum of 5% Ce doped La3Si6.5Al1.5N9.5O5.5 phosphor shows a broad excitation band from UV to 420 nm. Excitation at 355 nm yields a narrow 5d-4f emission band (FWHM = 68 nm) centered at 425 nm. Its emission band can be shifted from 418 nm at 0.5% Ce to 450 nm at 50% Ce. Internal quantum efficiency up to 84% can be achieved for a 1% Ce doped sample. Compared to La N(ew) phase without Al (La3Si8N11O4),[2] Al substitution improves the emission intensity and reduces thermal quenching without shifting the emission band. These performances show La3Si6.5Al1.5N9.5O5.5:Ce has great potential for UV-LED application. The local structure of La3Si6.5Al1.5N9.5O5.5 has also been investigated by solid state Nuclear Magnetic Resonance (NMR). 29Si MAS spectrum shows two peaks in a 3.36:1 intensity ratio at δSi = -54.7 ppm and δSi = -67.0 ppm, corresponding to an overall ([SiN4] + [SiN3O]):[SiN2O2] ratio of 3.36:1, as the chemical shifts of the [SiN4] and [SiN3O] tetrahedra are very similar. 27Al 3QMAS spectrum presents three distinct Al environments [AlO2N2], [AlO3N] and [AlO4], indicating that Al preferentially occupies more oxygen-rich sites.
Fig. 1 (a) Photoluminescence spectra of 5% Ce doped La3Si8-xAlxN11-xO4+x (x = 0, 1.5) at room temperature and temperature dependency of the emission intensity (inset). (b) crystal structure, (c) 29Si MAS NMR and (d) 27Al 2D 3QMAS NMR spectra of La3Si6.5Al1.5N9.5O5.5.
[1] J. Grins, Z. J. Shen, S. Esmaeilzadeh and P. Berastegui, J. Mater. Chem., 2001, 11, 2358 - 2362.
[2] B. Dierre, R.-J. Xie, N. Hirosaki and T. Sekiguchi, J. Mater. Res., 2007, 22, 1933 - 1941.
In this work, we have obtained phase pure non-doped sample and blue-emitting La3Si6.5Al1.5N9.5O5.5:Ce phosphor with solid-state reaction method for the first time. The excitation spectrum of 5% Ce doped La3Si6.5Al1.5N9.5O5.5 phosphor shows a broad excitation band from UV to 420 nm. Excitation at 355 nm yields a narrow 5d-4f emission band (FWHM = 68 nm) centered at 425 nm. Its emission band can be shifted from 418 nm at 0.5% Ce to 450 nm at 50% Ce. Internal quantum efficiency up to 84% can be achieved for a 1% Ce doped sample. Compared to La N(ew) phase without Al (La3Si8N11O4),[2] Al substitution improves the emission intensity and reduces thermal quenching without shifting the emission band. These performances show La3Si6.5Al1.5N9.5O5.5:Ce has great potential for UV-LED application. The local structure of La3Si6.5Al1.5N9.5O5.5 has also been investigated by solid state Nuclear Magnetic Resonance (NMR). 29Si MAS spectrum shows two peaks in a 3.36:1 intensity ratio at δSi = -54.7 ppm and δSi = -67.0 ppm, corresponding to an overall ([SiN4] + [SiN3O]):[SiN2O2] ratio of 3.36:1, as the chemical shifts of the [SiN4] and [SiN3O] tetrahedra are very similar. 27Al 3QMAS spectrum presents three distinct Al environments [AlO2N2], [AlO3N] and [AlO4], indicating that Al preferentially occupies more oxygen-rich sites.
Fig. 1 (a) Photoluminescence spectra of 5% Ce doped La3Si8-xAlxN11-xO4+x (x = 0, 1.5) at room temperature and temperature dependency of the emission intensity (inset). (b) crystal structure, (c) 29Si MAS NMR and (d) 27Al 2D 3QMAS NMR spectra of La3Si6.5Al1.5N9.5O5.5.
[1] J. Grins, Z. J. Shen, S. Esmaeilzadeh and P. Berastegui, J. Mater. Chem., 2001, 11, 2358 - 2362.
[2] B. Dierre, R.-J. Xie, N. Hirosaki and T. Sekiguchi, J. Mater. Res., 2007, 22, 1933 - 1941.