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The crystal structure of a Eu 2+ -activated SrCaSiAl 2 O 7 phosphor was refined and determined as a tetragonal structure with the refinement converged to R p ¼ 7.05%, R wp ¼ 10.67%, and c 2 ¼ 2.637 by Rietveld refinement using a synchrotron light source. By doping different contents of Eu 2+ , the emission peaks gives a range between 526 nm and 535 nm. The estimated Stokes shifts and Commission International de l'Eclairage (CIE) chromaticity coordinates are 16576-16896 cm À1 and (0.3155, 0.5073) to (0.3685, 0.5284), respectively. By tuning the ratio of phosphors and silicone, the optical properties of the three-band white LEDs could be tuned, changing the CIE chromaticity coordinates from yellow (0.4343, 0.4857) to white-light (0.3311, 0.3460), the correlated color temperature (CCT) between 3599 K and 5558 K, and color rendering index (Ra) in the range 83.1 to 79.1, under a forward bias current of 350 mA.

A Eu(2+)-activated Ca3Si2O7:Eu(2+) orangish-yellow-emitting phosphor with strong luminescence was synthesized and its crystal structure was determined on the basis of XRD profiles using synchrotron radiation. The crystal structure was refined by the Rietveld refinement method. The excitation and emission spectra of the Ca3Si2O7:Eu(2+) phosphor show broad excitation bands in the range of 240-550 nm and a broad yellow emission band centered at 603 nm, depending on the concentration of Eu(2+). The optimized concentration of Eu(2+) in the Ca3Si2O7:Eu(2+) phosphor was determined to be 0.015 mol. The critical distance and average decay time were found to be short and fast, respectively, ranging from 19.74 Å to 13.69 Å and from 2.56 μs to 2.34 μs on increasing the Eu(2+) doping content. Warm-white light-emitting diodes (LEDs) fabricated using an InGaN-based blue LED chip combined with the Ca3Si2O7:0.015Eu(2+) phosphor gave color rendering indices between 76.0 and 38.9, correlated color temperatures between 1924 K and 4992 K, and tuned CIE chromaticity coordinates in the range from orangish-yellow (0.543, 0.389) to reddish purple (0.333, 0.219). The color coordinates and emission intensity of a Ca3Si2O7:0.015Eu(2+)-based white LED display were slightly yellow-shifted and the intensity increased on increasing the forward-bias current. These results indicate that orangish-yellow-emitting Ca3Si2O7:0.015Eu(2+) can serve as a promising candidate for applications in warm-white LEDs.

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