Phase pure nondoped and Ce doped La3Si6.5Al1.5N9.5O5.5 (Al containing La N-phase) samples have been obtained by solid-state reaction synthesis for the first time. 1% Ce-doped La3Si6.5Al1.5N9.5O5.5 phosphor displays a broad excitation band ranging from UV to 410 nm, with a maximum at 355 nm. UV light excitation results in a narrow Ce3+ 5d-4f emission band (fwhm = 68 nm) centered at 418 nm. The emission can be tuned from 417 nm at 0.5% Ce to 450 nm at 50% Ce. A high internal quantum efficiency up to 84% is achieved for a 1% Ce doped sample, which has CIE chromaticity coordinates of x = 0.157 and y = 0.069, close to the NTSC blue standard (x = 0.155; y = 0.070). Compared to La3Si8O4N11:Ce phosphor, the quantum efficiency and thermal stability have been enhanced for La3Si6.5Al1.5N9.5O5.5:Ce phosphor without shifting the emission peak wavelength. La3Si6.5Al1.5N9.5O5.5:Ce shows less thermal quenching than La3Si8O4N11:Ce and no shift or change in the shape of emission spectra with increasing the temperature from 4 to 573 K. These results show that La3Si6.5Al1.5N9.5O5.5:Ce is more efficient than any other (oxy-)nitride phosphor with an emission in the short wavelength blue region (400–450 nm). A white LED was fabricated using the La3Si6.5Al1.5N9.5O5.5:5%Ce as a blue phosphor. The high color rendering index (Ra = 93.2, R9 = 91.4, and R12 = 89.5) obtained shows that the phosphor is a very promising conversion phosphor for white LEDs.Keywords: deep blue; high color rendering; high efficiency; La3Si6.5Al1.5N9.5O5.5:Ce; luminescence; sialon; white LED;

La2O3, LaN, Si3N4, AlN and CeO2 have been used as starting materials to synthesize Ce doped LaAl(Si6−zAlz)(N10−zOz) (z ≈ 1, termed the JEM phase) phosphors, via a solid-state reaction method in a gas pressure furnace at a high temperature. Nearly single phase JEM:Ce phosphors have been obtained by carefully controlling the synthesis conditions. The 5% Ce doped JEM phosphor displays a broad excitation band extending from UV to 425 nm, with a maximum at 355 nm. Excitation with 355 nm light results in a Ce3+ 5d–4f emission band (FWHM = 81 nm) centered at 430 nm, with a high internal quantum efficiency of 75%. The emission of the JEM:0.01Ce phosphor has only quenched 3% at room temperature as compared to the intensity at 4 K and still 57% of the luminescence is left at 573 K, which is superior to JEM:Eu phosphors. These performances make JEM:Ce phosphors very promising blue-emitting phosphors for white LED applications.

The narrow-band green-emitting phosphor Ba2LiSi7AlN12:Eu2+ was discovered by analyzing a single particle in a powder mixture, which we call the single particle diagnosis approach. Single crystal X-ray diffraction analysis of the particle revealed that Ba2LiSi7AlN12:Eu2+ crystallizes in the Pnnm space group (No. 58) with a = 14.0941 Å, b = 4.8924 Å, c = 8.0645 Å, and Z = 2. The crystal structure is composed of a corner-sharing (Si,Al)N4 corrugated layer and edge-sharing (Si,Al)N4 and LiN4 tetrahedra. Ba(Eu) occupies the one-dimensional channel in a zigzag manner. The luminescence properties were also measured using a single crystalline particle. Ba2LiSi7AlN12:Eu2+ shows a green luminescence peak at approximately 515 nm with a narrow full-width at half-maximum of 61 nm. It shows high quantum efficiency of 79% with 405 nm excitation and a small decrease of luminescence intensity even at 300 °C.

The valence and coordination structure of manganese in a Mn,Mg-codoped γ-AlON spinel-type oxynitride green phosphor were studied by synchrotron X-ray diffraction and absorption fine structure measurements. The absorption edge position of the XANES revealed the bivalency of Mn. Two cation sites are available in the spinel structure for cation doping: a tetrahedral site and an octahedral site. The pre-edge of the XANES and the distance to the nearest neighbor atoms obtained from the EXAFS measurement showed that Mn was situated at the tetrahedral site. Rietveld analysis showed that the vacancy occupied the octahedral site. The preferential occupation of the tetrahedral site by Mn and the roles of N and Mg are discussed in relation to the spinel crystal structure.Graphical AbstractFourier transform of EXAFS of Mn K-edge for Mn,Mg-codoped green phosphor and Mn coordination structure.Highlights► Mn, Mg-codoped γ-AlON green phosphor for white LED. ► The valence of Mn is divalent. ► Mn occupies the tetrahedral site in the spinel structure.

Eu, Si co-doped AlN shows blue luminescence by UV and electron excitation. However, it is not clear how Eu is located in a wurtzite AlN lattice as there is not enough space for a large Eu cation. In the present study, Eu, Si co-doped AlN is analyzed to elucidate the luminescent Eu center’s location and the role of co-dopant Si. The XRD shows that the lattice parameters decrease compared to Eu solely doped AlN and undoped AlN due to Si doping in the AlN lattice. The Eu solely doped product shows impurity phase contamination with a reddish body color. Si co-doping is essential for Eu incorporation into AlN. TEM-EDS and HAADF-STEM measurements clarify that Eu forms a single layer structure with the Si condensation between the AlN wurtzite blocks. Another Si layer condensation is observed at the half position between Eu layers. Electron diffraction shows that there is no apparent long range ordering of Eu layer. The XAFS study shows that all the Eu in the product has a divalent valence and that the bond distance to the first neighboring anion is long at 0.315(8) nm. This is in good agreement with the model structure and the blue emission property. This result indicates that layer type doping can be a used to design new phosphors.

New phosphors are required for the advancement of lighting and display technologies. One of the most effective ways for new phosphors is to employ new materials for host materials. It takes much time and labor to develop new materials from powder synthesis or single crystal growth. However, even if the powder product is a mixture phase, each particle is a single phase and a single crystal. The single particle diagnosis approach focuses on the tiny single crystal particle. Here we show the concept of the single particle diagnosis approach and some examples of new phosphor discovery by this approach.Download full-size image

Eu, Si co-doped AlN shows blue luminescence by UV and electron excitation. However, it is not clear how Eu is located in a wurtzite AlN lattice as there is not enough space for a large Eu cation. In the present study, Eu, Si co-doped AlN is analyzed to elucidate the luminescent Eu center’s location and the role of co-dopant Si. The XRD shows that the lattice parameters decrease compared to Eu solely doped AlN and undoped AlN due to Si doping in the AlN lattice. The Eu solely doped product shows impurity phase contamination with a reddish body color. Si co-doping is essential for Eu incorporation into AlN. TEM-EDS and HAADF-STEM measurements clarify that Eu forms a single layer structure with the Si condensation between the AlN wurtzite blocks. Another Si layer condensation is observed at the half position between Eu layers. Electron diffraction shows that there is no apparent long range ordering of Eu layer. The XAFS study shows that all the Eu in the product has a divalent valence and that the bond distance to the first neighboring anion is long at 0.315(8) nm. This is in good agreement with the model structure and the blue emission property. This result indicates that layer type doping can be a used to design new phosphors.