Sr8MgGd(PO4)7:Eu2+: yellow-emitting phosphor for application in near-ultraviolet-emitting diode based white-light LEDs

Abstract

The yellow-emitting phosphor Sr₈MgGd(PO₄)₇:xEu²⁺ (SMGP:xEu²⁺) was successfully synthesized by a solid-state reaction and used for the first time to fabricate white light-emitting diodes (LEDs) with excellent color rendering index (CRI). Furthermore, the luminescence properties‚ reflectance spectra and fabricated LEDs were firstly investigated. The excitation and reflectance spectra of this phosphor show broad band excitation and absorption in the 240–470 nm near ultraviolet (NUV) region, indicating its potential application in NUV diode based white-light LEDs. Upon excitation at 385 nm, the Eu²⁺ doped SMGP phosphors showed strong yellow emission centered at 512 and 606 nm, which could be ascribed to the 4f⁶5d¹ → 4f⁷ transitions of Eu²⁺. The optimal doping concentration of Eu²⁺ in SMGP was determined to be 0.01 mol. Non-radiative transitions between the Eu²⁺ ions in the SMGP host were demonstrated to be attributable to dipole–dipole interactions. A white-light NUV LED was fabricated using a phosphor blend of SMGP:0.01Eu²⁺ and BAM:Eu²⁺ pumped by a 385 nm NUV chip, driven by a 350 mA current. The color, chromaticity coordinates (x, y), correlated color temperature (CCT) and Commission Internationale de l'Eclairage (CIE) coordinates can be tuned from yellow ((0.442, 0.481), 3456 K, 75.4) through warm white-light ((0.350, 0.348), 4804 K, 95.6) and eventually to white-light ((0.331, 0.321), 5592 K, 94.1) by weight ratio tuning of the SMGP:0.01Eu²⁺ and BAM:Eu²⁺ phosphors, and the luminous efficacy between 9.6 to 7.6 lm W⁻¹. We are currently evaluating the potential applications of SMGP:xEu²⁺ as a yellow-emitting near-ultraviolet (NUV) convertible phosphor in fabricating warm white-light LEDs with excellent CRI.