Photoluminescence Spectra Tuning Of Eu~(2+) Activated Orthosilicate Phosphors Used For White Light Emitting Diodes

摘要

Divalent europium activated alkaline earth orthosilicate M_2SiO_4 (M = Ba, Sr, Ca) phosphors were synthesized through solid-state reaction technique and their luminescent properties were investigated. Photoluminescence emission spectra of Sr_2SiO_4:Eu~(2+) phosphor was tuned by substitution of Sr~(2+) with 10 mol% Ca~(2+) or Mg~(2+). Two emission bands originated from the 4f-5d transition of Eu~(2+) ion doped into different cation sites in the M_2SiO_4 host lattice were observed under ultraviolet excitation. The Sr_2SiO_4:Eu~(2+) phosphor showed a blue and a green broad emission bands peaked around 475 and 555 nm with some variation for different Eu~(2+) doping concentration. When 10 mol% of Sr~(2+) was substituted by Ca~(2+) or Mg~(2+), the blue emission band blue-shifted to 460 nm and the green emission band shifted to even longer wavelength. An energy loss due to energy transfer from one Eu~(2+) to another Eu~(2+) ion, changing of the crystal field strength and covalence in the host lattice together were assigned for the tuning effect. With an overview of the excitation spectra and the emission spectra in blue and green-yellow color, these co-doped phosphors can become a promising phosphor candidate for white light-emitting-diodes (LEDs) pumped by ultraviolet chip.