Tunable emissions from Dy³⁺/Sm³⁺ ions co-activated SrY₂O₄:Er³⁺ nanocrystalline phosphors for LED and FED applications

Er³⁺ ions single-doped, Dy³⁺/Er³⁺ ions co-doped, and Er³⁺/Dy³⁺/Sm³⁺ ions triple-doped SrY₂O₄ nanocrystalline phosphors were synthesized by a citrate sol-gel method. X-ray diffraction patterns confirmed their pure orthorhombic structure after annealed at 1300 C and the morphology of particles was found to be nearly spherical. The Er³⁺ ions single-doped phosphor samples showed an intense green emission band around 548 nm and the concentration quenching occurred at dilute concentrations (1 mol%) because the ⁴S_3/2 energy state of Er³⁺ ions can be easily quenched by means of cross relaxation to a metastable state. The Dy ³⁺/Er³⁺ ions co-doped phosphors exhibited a classic yellowish green emission due to efficient energy transfer from Dy³⁺ to Er³⁺ ions under 365 nm excitation. By adding a series of Sm ³⁺ ions to the Dy³⁺/Er³⁺ ions co-doped SrY ₂O₄ phosphors, a pleasant white light emission which is essential for white light-emitting diodes was obtained. Likewise, from the cathodoluminescence measurements, a warm white light emission that is required for field-emission displays was achieved with accelerating voltage of 5 kV and filament current of 55 μA. A possible energy transfer mechanism was discussed and the energy transfer efficiencies were also calculated.