Ce-Doped La₃Si_6.5Al_1.5N_9.5O_5.5, a Rare Highly Efficient Blue-Emitting Phosphor at Short Wavelength toward High Color Rendering White LED Application

Phase pure nondoped and Ce doped La₃Si_6.5Al_1.5N_9.5O_5.5 (Al containing La N-phase) samples have been obtained by solid-state reaction synthesis for the first time. 1% Ce-doped La₃Si_6.5Al_1.5N_9.5O_5.5 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 <i>x</i> = 0.157 and <i>y</i> = 0.069, close to the NTSC blue standard (<i>x</i> = 0.155; <i>y</i> = 0.070). Compared to La₃Si₈O₄N₁₁:Ce phosphor, the quantum efficiency and thermal stability have been enhanced for La₃Si_6.5Al_1.5N_9.5O_5.5:Ce phosphor without shifting the emission peak wavelength. La₃Si_6.5Al_1.5N_9.5O_5.5: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 La₃Si_6.5Al_1.5N_9.5O_5.5: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 La₃Si_6.5Al_1.5N_9.5O_5.5:5Î 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

Visible tunable lighting system based on polymer composites embedding ZnO and metallic clusters: from colloids to thin films

<p>The development of phosphor devices free of heavy metal or rare earth elements is an important issue for environmental reasons and energy efficiency. Different mixtures of ZnO nanocrystals with Cs₂Mo₆I₈(OOC₂F₅)₆ cluster compound (CMIF) dispersed into polyvinylpyrrolidone matrix have been prepared by very simple and low cost solution chemistry. The resulting solutions have been used to fabricate highly transparent and luminescent films by dip coating free of heavy metal or rare earth elements. The luminescence properties of solution and dip-coated films were investigated. The luminescence of such a system is strongly dependent on the ratios between ZnO and CMIF amounts, the excitation wavelength and the nature of the system. By varying these two parameters (ratio and wavelength), a large variety of colors, from blue to red as well as white, can be achieved. In addition, differences in the luminescence properties have been observed between solutions and thin films as well as changes of CMIF emission band maximum wavelength. This may suggest some possible interactions between the different luminophore centers, such as energy transfer or ligands exchange on the Mo₆ clusters.</p