Novel Yellow-Emitting Sr8MgLn(PO4)7:Eu2+ (Ln = Y, La) Phosphors for Applications in White LEDs with Excellent Color Rendering Index

Eu2+-activated Sr8MgY(PO4)7 and Sr8MgLa(PO4)7 yellow-emitting phosphors were successfully synthesized by solid-state reactions for applications in excellent color rendering index white light-emitting diodes (LEDs). The excitation and reflectance spectra of these phosphors show broad band excitation and absorption in the 250–450 nm near-ultraviolet region, which is ascribed to the 4f7 → 4f65d1 transitions of Eu2+. Therefore, these phosphors meet the application requirements for near-UV LED chips. Upon excitation at 400 nm, the Sr8MgY(PO4)7:Eu2+ and Sr8MgLa(PO4)7:Eu2+ phosphors exhibit strong yellow emissions centered at 518, 610, and 611 nm with better thermal stability than (Ba,Sr)2SiO4 (570 nm) commodity phosphors. The composition-optimized concentrations of Eu2+ in Sr8MgLa(PO4)7:Eu2+ and Sr8MgY(PO4)7:Eu2+ phosphors were determined to be 0.01 and 0.03 mol, respectively. A warm white-light near-UV LED was fabricated using a near-UV 400 nm chip pumped by a phosphor blend of blue-emitting BaMgAl10O17:Eu2+ and yellow-emitting Sr8MgY(PO4)7:0.01Eu2+ or Sr8MgLa(PO4)7:0.03Eu2+, driven by a 350 mA current. The Sr8MgY(PO4)7:0.01Eu2+ and Sr8MgLa(PO4)7:0.03Eu2+ containing LEDs produced a white light with Commission International de I'Eclairage (CIE) chromaticity coordinates of (0.348, 0.357) and (0.365, 0.328), warm correlated color temperatures of 4705 and 4100 K, and excellent color rendering indices of 95.375 and 91.75, respectively.