Luminescence properties of single-phase color-tunable Li4SrCa(Si2O4N8/3):Eu2+ phosphor for white light-emitting diodes

Abstract

A novel single-phase color-tunable phosphor, Eu²⁺-activated Li₄SrCa(Si₂O₄N_8/3):Eu²⁺ (LSCSN:Eu²⁺), was synthesized via the conventional solid-state reaction method. The crystal structure of LSCSN has been determined by Rietveld refinement on X-ray powder diffraction data, and it was found that LSCSN crystallizes in an orthorhombic unit cell with the space group Pbcm(57). Under the excitation of UV light, the phosphor shows two main emission bands peaking at 430 nm and 578 nm, which have been confirmed to correspond to Eu²⁺ occupying the ten-coordination Sr sites and six-coordination Ca sites, respectively. Subsequently, the energy transfer between different Eu²⁺ emission centers was verified by the overlap of the emission and excitation spectra and the variation of fluorescence decay lifetimes. Meanwhile, when the excitation was changed to 375 nm light, it was found that the color hue can be tuned from blue to yellow, and even white if the Eu²⁺ ion concentration was increased to some extent. The thermal stability of the phosphor has been also investigated, which performs well with a high value of stability along with its integrated emission intensity remaining as 90.9% at 150 °C of that measured at room temperature. Furthermore, a warm white LED has been fabricated with a LSCSN:0.03Eu²⁺ phosphor and a 375 nm LED chip, and when the applied current is set to be 80 mA, the white LED was found to have a color rendering index (R_a) of 82.5 at the CIE coordinates of (0.3568, 0.3111) and correlated color temperature of 3318 K. The outstanding luminescence properties suggested that our prepared samples have potential application in w-LEDs.