Synthesis And Photoluminescence Properties Of Ca_2-xSm_xSn_1-yMyO₄ (M＝Ce,Ti) Phosphors

Ca₂SnO₄:Sm³⁺,Ca₂SnO₄: (Ce⁴⁺,Sm³⁺) and Ca₂SnO₄: (Ti⁴⁺,Sm³⁺) phosphor powders weresynthesized by a solid-state reaction method and their structures and luminescent properties wereinvestigated by using testing techniques such as X-ray diffraction (XRD), fluorescence spectraand decay lifetime. The XRD results reveal that the crystal structure of Ca₂SnO₄ remainsunchanged in Sm³⁺-doped, Ce⁴⁺/Sm³⁺ or Ti⁴⁺/Sm³⁺-codoped Ca₂SnO₄.The Sm³⁺ ions haveunusual emission characteristics in Ca₂SnO₄.Only the transitions between ⁴G_5/2 and 6H5/2, ⁶H_7/2occur, and that between ⁴G_5/2and 6H9/2 does not happen. The yellow emission of the transition⁴G_5/2-6H5/2 is the strongest, rather than the usual red emission transition ⁴G_5/2-⁶H_7/2. In theCa₂SnO₄:Sm³⁺ sample there exists Sm³⁺-O₂^- charge transfer absorption band covering the rangefrom 210 to 340nm, with two broadband peaks at 247 nm and 277 nm. The Sm³⁺ ion has twofluorescence lifetimes of ? 1 ?0.74msand ? 2 ?4.80ms.The emission spectra of Ca_2-xSm_xSn_1-yCeyO₄ include Ce⁴⁺ - O₂^- charge-transferbroadband and ⁴G_5/2-6HJ(J=5/2,7/2,9/2) lines of Sm³⁺, the emissions of two centers changeconsiderably with the concentrations of Ce⁴⁺ or Sm³⁺. Blue emission of Ce⁴⁺-O₂^-, yellow andred luminescence of Sm³⁺ coexist in Ca_2-xSm_xSn_1-yCeyO₄ with low concentrations of Sm³⁺whereas only Sm³⁺ emission occurs at higher Sm³⁺ concentrations. By changing the dopingconcentrations, the light color of the sample can be adjusted. The blue luminescence of Ce⁴⁺-O₂^- originates from the charge-transfer absorption of Ce⁴⁺-O₂^-, whose lifetime is about 76μs, however, the Sm³⁺ emission originates from that of Sm³⁺-O₂^-. There is no energy transferbetween Ce⁴⁺ and Sm³⁺.The emission spectra of Ca_2-xSm_xSn_1-yTi_yO₄ comprise Ti⁴⁺ - O₂^- charge-transferbroadband and ⁴G_5/2-6HJ(J=5/2,7/2,9/2) lines of Sm³⁺. The luminescence of Ti⁴⁺-O₂^- and Sm³⁺coexist in Ca_2-xSm_xSn_1-yTi_yO₄ with low concentrations of Sm³⁺ whereas only Sm³⁺ emissionoccurs at higher Sm³⁺ concentrations. By changing the doping concentrations, the light color ofthe sample can be adjusted. The emission energy of Ti⁴⁺-O₂^-and Sm³⁺ originates from the Ti⁴⁺-O₂^- charge transfer absorption, the absorption band locates around 276 nm.The energy transferbetween Ti⁴⁺-O₂^- and Sm³⁺ is achieved throughradiationlessprocess.