Luminescence properties, energy transfer and multisite luminescence of Bi3+/Sm3+/Eu3+-coactivated Ca20Al26Mg3Si3O68 as a potential phosphor for white-light LEDs

Abstract

A series of blue-to-red emitting Ca₂₀Al₂₆Mg₃Si₃O₆₈:Bi³⁺/Sm³⁺/Eu³⁺ phosphors were synthesized via a high temperature solid-state reaction method. The crystal structure, luminescence properties, energy transfer and multisite luminescence were investigated in detail. Under ultraviolet (UV) light excitation of 343 nm, Bi³⁺-doped Ca₂₀Al₂₆Mg₃Si₃O₆₈ phosphors exhibit a broad blue emission band from 370 to 600 nm which is derived from the allowed transition ³P₁ → ¹S₀ of Bi³⁺ ions. The Ca₂₀Al₂₆Mg₃Si₃O₆₈:Sm³⁺ samples show orange-reddish emission bands at 561, 598, 649 and 708 nm under the excitation of 401 nm. The red emission of Ca₂₀Al₂₆Mg₃Si₃O₆₈:Eu³⁺ samples at 587, 616, 654 and 700 nm were detected under the excitation of 392 nm, due to ⁵D₀ → ⁷F_K (K = 1, 2, 3, and 4) transitions. In addition, two kinds of sites for cations (Ca²⁺) in the host were considered from the high resolution site-selective spectroscopy of Ca₂₀Al₂₆Mg₃Si₃O₆₈:Eu³⁺ at low temperature, which matches with the crystal structure of Ca₂₀Al₂₆Mg₃Si₃O₆₈. Meanwhile, in the Bi³⁺, Sm³⁺ co-doped Ca₂₀Al₂₆Mg₃Si₃O₆₈ samples, the energy transfer from Bi³⁺ to Sm³⁺ can be found from the photoluminescence spectra and the fluorescence decay curves. The emission hue can be tuned from cool white (0.270, 0.267) to white (0.334, 0.293), and finally to warm white light (0.405, 0.317) by suitably varying the ratio of Bi³⁺/Sm³⁺, indicating that the developed phosphor may be potentially used as a single-component white-emitting phosphor for UV light-emitting diodes. The phosphors CAMSO:Bi³⁺,Eu³⁺ develop excellent red-emission properties, so that the Eu³⁺ doped samples have potential application in WLED.