Luminescence Properties Of Persistent Phosphors Gd₃Al₂Ga₃O₁₂ For AC-LEDs

Alternating Current?AC?LED,which can be driven directly by urban AC power,is quickly becoming a hot spot in the field of international lighting.Compared with Direct Current?DC?LED,AC-LED abandons the AC-DC conversion device that used in DC-LED device.Therefore,AC-LED has the advantages of better energy saving,longer lifetime,higher efficiency and lower cost than DC-LED.At present,the phosphor used in AC-LED is still traditional powder,and there is a dark time of 5-20 ms in the AC circuit operation cycle.This cycle cannot be compensated and leading to the occurrence of flicker problem in AC-LED.In order to solve this problem,researchers propose to add afterglow phosphors in the AC-LED device and compensate for the dark time in the AC circuit by using its afterglow.Meanwhile,this scheme will not change the structure of the AC-LED system.Therefore,the proposed afterglow phosphor is the best solution to the flicker in AC-LED.The main purpose of this work is to solve the flicker in AC-LED.Therefore,we study on the matrix material of gadolinium gallium aluminum garnet structure system with excellent afterglow properties.The main research contents are as follows:?1?We synthesized the persistent phosphor GAGG:Ce³⁺through two-step solid-state reactions?first sintered in an O₂ atmosphere and then annealed in a CO reducing atmosphere?.The phase evolution,luminescence,persistent luminescence,and thermal stabilities of GAGG:Ce³⁺were investigated.Comparing with the samples sintered only in O₂,the samples annealed in CO show higher luminescence and afterglow and better thermal stability.Under 445nm excitation,the afterglow spectra of GAGG:Ce³⁺shows the same profile as the PL spectrum,displaying a broad yellow emission with a peak around 545nm.By optimizing the sintering process,the internal quantum efficiency can reach as high as 71.3%.The time?₈₀ is about 15 ms,which is much longer than0.4 ms required for alternating current?AC?-LEDs.These results indicate the promising application of the GAGG:Ce³⁺persistent phosphor for reducing flicker from AC-LEDs.?2?GAGG:3%Ce³⁺was synthesized under three different sintering processes:?a?sintered firstly in air or?b?in O₂ atmosphere,and then annealed in CO reducing atmosphere,?c?the samples were directly sintered in CO reducing atmosphere.The luminescence and afterglow characteristics of three kinds of samples were studied.These results indicate that the luminescence and afterglow properties have been greatly improved for the samples obtained by the two step sintering method.The maximum internal quantum efficiency is up to81.9%.?3?The effect of different concentration of Ce³⁺and Dy³⁺doped on the luminescence properties of GAGG:Ce³⁺were studied.When Ce³⁺concentration is 8%,the internal and external quantum efficiency reaches the maximum,which are 86.1%and 57.6%,respectively.By doping trace Dy³⁺,the afterglow luminescence and life of GAGG:8%Ce³⁺have been greatly improved.When the sample GAGG:8%Ce³⁺,0.5%Dy³⁺is applied to AC-LED,the flicker index can be reduced from 100%to 82.9%.The study shows that the doping of Dy³⁺ions is the role of the trap center.