The Luminescence Properties Of Silicate Phosphor Based On White LED

Phosphors converted White light-emitting diodes?LED?have been solid-state light source to the fluorescent and incandescent lamps due to its long lifetime,high luminous efficiency,energy saving,and environmental friendly characteristics.The commercial method to synthesize white pc-LEDs involves the combination of a blue LED chip with a yellow phosphor YAG: Ce³⁺.The major shorting comings is that the complex has a not ideal color rendering index?CRI,Ra < 80?and a high correlated color temperature?CCT,TC > 5500 K?because of the short of a red component.In order to overcome these shortcoming,many researches have been targeted at combine red,green,and blue tricolor emission phosphors?RGB phosphors?or a single-phased tunable emission phosphor with an ultraviolet?300–410nm?LED chip,which exhibit better color stability as well as outstanding CRI and tunable CCT.However,RGB phosphors suffer from low efficiency owing to self-absorption among phosphor particles.Therefore it is an active topic to study single-phased tunable emission phosphors for UV-chip white LEDs.The phosphor Gd_4.67Si₃O₁₃: Tb³⁺,Ce³⁺ and MgY₂Si₃O₁₀: Bi³⁺,Eu³⁺ have been synthesized by high-temperature solid-state method.The phase purity and structure were characterized by powder X-ray diffraction?XRD?with a Cu target radiation resource?? = 1.54078 ??.The photoluminescence excitation?PLE?spectra and photoluminescence?PL?spectra were obtained using a Hitachi F-4600 fluorescence spectrophotometer with a 150 W Xe-arc lamp.The absolute photoluminescence quantum yield was measured using the FLS980 fluorescence spectrophotometer with the integrating sphere.The decay curves were measure by using FLS980 with 320 nm nano-LED pulse laser radiation.All data including the structural characteristics,temperature stability and colorimetric characteristics indicate that silicate phosphor is promising phosphor for UV-chip W-LEDs.There are five chapters: the first is the general history and some related theories,including rare earth ions energy levels,concentration quenching.The second one describes the raw materials,characterization equipment and method.The third introduces the detailed investigations on Gd_4.67Si₃O₁₃: Tb³⁺,Ce³⁺.The fourth focuses on MgY₂Si₃O₁₀ phosphor,especially the energy transfer efficiency and mechanism.The five is the conclusion.Major content and results were as follows:1.Gd_4.67Si₃O₁₃:Ce³⁺,Tb³⁺ phosphor has been prepared by the conventional high-temperature solid-state method at 1350 oC for 6 h.Under 290-nm excitation,the energy transfer processes from Ce³⁺ and Tb³⁺ ions has been demonstrated to be a resonant type via the dipole-dipole mechanism and the energy transfer critical distance has been discussed by Dester's theory,it is 21.03 ?.The emission spectrum consisted of the blue band emission of Ce³⁺ and the green peaks emission of Tb³⁺,so the emission color adjust from blue to bluish-green to green.The phosphor has good thermal quenching properties.Its intensities decreased to 80% of the initial intensity?50°C?at 150°C and it does not decrease to half at 3000 C.2.A series of novel phosphor MgY₂Si₃O₁₀:Bi³⁺,Eu³⁺ has been synthesized by a conventional high-temperature solid-state method at 1350 oC for 6 h.Under UV-light excitation,there is an efficient energy transfer from Bi³⁺ to Eu³⁺ via a dipole-quadrupole interaction mechanism.The critical distance of energy transfer from Bi³⁺ to Eu³⁺ is calculated to be 13 ?,and in this work the maximum efficiency of energy transfer in this concentration interval is about 65%.The emission color of phosphor MgY₂Si₃O₁₀:Bi³⁺,Eu³⁺ can be tuned from the blue region?0.181,0.287?through white?x=0.333,y=0.306?to the red region?0.579,0.349?by adjusting the concentration of Bi³⁺,Eu³⁺ dopants.A white light with CCT = 5419 K and CIE =?0.333,0.306?has been realized upon 344 nm excitation,indicating that MgY₂Si₃O₁₀:Bi³⁺,Eu³⁺ phosphor is a promising single-phased tunable emission phosphor for UV-chip W-LEDs.