White-Light Generation in Sr[sub 2]SiO[sub 4]:Eu[sup 2+], Ce[sup 3+] under Near-UV Excitation

Abstract

White-light emission is generated by combining blue and blue green to yellow emissions of Ce 3+ and Eu 2+ , respectively, in a single host lattice of Sr 2 SiO 4 . The excitation is in the near-UV region ͑350-370 nm͒. The role of concentration of Eu 2+ on the photoluminescence emission intensity in Sr 2-x Eu x SiO 4 ͓x = 0.0025, 0.005, 0.0075, and 0.01͔ is studied, and it is found that the critical concentration is 0.0025 mol. Energy migration over Eu 2+ sites occurs, resulting in concentration quenching. Ce 3+ exhibits a high absorption in the near-UV region. Energy transfer from Ce 3+ to Eu 2+ occurs in Sr 2 SiO 4 :Eu 2+ , Ce 3+ . Optimization of concentration of Eu 2+ to produce white light in Sr 1.98-x Eu x Ce 0.01 Li 0.01 SiO 4 shows that the optimum concentrations of Ce 3+ and Eu 2+ are 0.01 and 0.0025 mols, respectively. Partial energy transfer from Ce 3+ to Eu 2+ is responsible for the white-light generation. The results reveal that Sr 2 SiO 4 :Eu 2+ , Ce 3+ is an efficient "single host lattice phosphor" for solid-state lighting technology using UV light-emitting diode ͑LED͒ to generate white light.

Enhanced luminescence of Y3Al5O12:Ce3+ nanophosphor for white light-emitting diodes

“…The next higher state originates from the 5d state and 4f-5d transitions are parity and spin allowed. 16 The 5d state is split by crystal field and, hence, there are three Ce 3+ absorption bands in the excitation spectrum located at 225, 345 and 450 nm ͑see Fig. 2͒.…”

Structural characterization and optical properties of dysprosium doped strontium calcium magnesium di-silicate phosphor by solid state reaction method

“…After irradiation with the ultraviolet light (process numbered [1]), most of the excitation energy associated with the excited carriers (electrons or holes) will be transferred via the host directly to the luminescence centres, Dy 3+ , followed by the Dy 3+ 4f emissions as the immediate luminescence (process [2]). However, part of the excitation energy will be stored when some of the excited carriers drop into the traps (process [3]), instead of returning to the ground states. Later, with thermal excitation at proper temperature, these carriers will be released from the traps and transferred via the host to the Dy 3+ ions, followed by the characteristic Dy 3+ emissions as long afterglow (process [4]).…”

“…The strategies used to produce white light in LEDs include combining blue LED with a yellow phosphor or UV-LED with blue, green and red phosphors or blue, green and red LEDs. [2][3] Luminescence materials doped with Dy 3+ have recently drawn considerable interest because it emits white light. Given that Dy 3+ with 4f 9 configuration has complicated f-block energy levels, various possible transitions between these levels are highly selective and show sharp line spectra.…”

Fluorescence enhancement of single-phase red-blue emitting Ba3MgSi2O8:Eu2+,Mn2+ phosphors via Dy3+ addition for plant cultivation

“…where Q is the position in energy for the lower d-band edge for the free ions, generally 34000 cm -1 [10] for Eu 2+ ; V is the valence of the active cation, here V = 2 for Eu 2+ ; n is the coordination number of the active cation for the anion, and two different sites of Ba 2+ are 12 and 10 [11] for Ba 3 MgSi 2 O 8 : Eu 2+ ,Mn 2+ phosphor,respectively, ea is the electron affinity of the atoms forming anions, as it is 1.6 [10] for O 2-; r is the radius of the host cation replaced by the active cation in the host crystal, accordingly, the ion radius are 1.75 and 1.66Å [12,13] .According to values mentioned above, the emission peaks position of Eu 2+ in the different sites are shown in Tab.1.…”