Abstract
A series of high-efficiency narrow band red-emitting La2 M2 O9 :Eu3+ (M = Mo/W) phosphors for white LEDs was synthesized using a conventional solid-state reaction method. All the compositions show absorption in the near ultraviolet (UV) light region due to charge transfer from O to M (M = W and Mo). In order to investigate the luminescence quenching effect, the Eu3+ concentration was varied in the La2 M2 O9 lattice. The tungstate analogue had a quantum yield of 46.5%, whereas the molybdate equivalent had a comparatively subordinate value (15.4%). The phosphor could be competently excited by ~395 or 465 nm photons (could be integrated well with a near-UV or blue LED chip) and showed dominant red emission electric-dipole transition (5 D0 →7 F2 ) with sharp spectral lines due to 4f-4f electronic transition of the Eu3+ ion and potential red-emitting colour converters for white LEDs. The red LED was fabricated by integrating the best phosphor composition with a near-UV LED and a white hybrid LED was fabricated by conjugating with a yellow organic dye and a red phosphor with near-UV LEDs. The white hybrid LED showed an excellent colour rendering index (83%), with CIE colour coordinates (0.313, 0.365) and CCT (6280 K).
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