Preparation And Optical Properties Of Rare Earth Doped CaMoO₄/SrMoO₄ Luminescent Thin Films

LEDs are widely used in the fields of display panels and lighting due to the characteristics of efficient and environmentally friendly solid-state light emitters.Furthermore,the light-emitting layer is a vital part of the electroluminescent devices.In recent decades,many researchers focused their eyes on the semiconductor fluorescent films and reported many works.In the study of luminescent materials,it has been found that scheelite-type molybdate materials have stable physical and chemical properties,high compatibility with light-emitting ions,and exhibit semiconductor properties owing to their narrow optical band gaps.So molybdate materials are suitable as a host for luminescent materials.The characteristics of narrow band emission,high color purity and high luminous efficiency of rare earth ions make them uniquely advantageous in the field of luminescence.Although several preparation methods of rare earth-doped molybdate luminescent materials have been reported in recent years,they are mainly concentrated in bulk phosphors.So there are still many places need be further optimized in terms of rare earth-doped molybdate thin film materials.In this thesis,we developed a facile solution approach to fabricate rare earth-doped molybdate luminescent thin films,which is also suitable for other luminescent thin films.The detailed contents are as follows:1.We fabricated Eu³⁺doped CaMoO₄/SrMoO₄ red luminescent thin films by the butylamine-butyric acid solution approach.Then,we systematically studied the effects of Eu³⁺doping concentration,annealing temperature and Na+/K+/Li+doping concentration on PL intensity.According to testing and analysis,the optimal chemical compositions are Ca0.87MoO₄:Eu0.10³⁺,K0.0³⁺?annealed at 500 ?for 2 h?and Sr0.82MoO₄:Eu0.15³⁺,K0.0³⁺?annealed at 650? for 2 h?.Their PL lifetimes are 0.48 ms and 0.45 ms and the band gaps?Eg?are 4.7 eV and 4.8 eV,respectively.In addition,the luminescent thin films are uniform and crack-free.2.Tb³⁺doped CaMoO₄/SrMoO₄ green luminescent thin films were fabricated by the same solution approach.And we also systematically investigated the effects of Tb³⁺doping concentration,annealing temperature and Na+/K+/Li+doping concentration on PL intensity.Ca0.87MoO₄:Tb0.03³⁺,Li0.10+?annealed at 650? for 2 h?and Sr0.82MoO₄:Tb0.15³⁺,Li0.0³⁺?annealed at 650? for 2 h?are the optimal doping compositions.Their PL lifetimes are 0.46 ms and 0.45 ms and the band gaps?Eg?are 4.67 eV and 4.82 eV,respectively.In addition,we prepared Sm³⁺/Dy³⁺doped CaMoO₄/SrMoO₄ luminescent thin films by the solution approach and investigated the effects of rare earth ions doping concentration and annealing temperature on PL intensity.The optimal doping compositions are Ca_0.97MoO₄:Sm_0.03³⁺.?annealed at 650?for 2 h?,Sr_0.90MoO₄:Sm_0.10³⁺?annealed at 550? for 2 h?and Ca_0.99MoO₄:Dy_0.01³⁺?annealed at 650? for 2 h?.3.There is an energy transfer between Eu³⁺and Tb³⁺,so we fabricated Eu³⁺and Tb³⁺co-doped CaMoO₄/SrMoO₄ luminescent thin films by the solution method.The energy transfer from Tb³⁺ions to Eu³⁺ions in Tb³⁺and Eu³⁺ co-doped CaMoO₄/SrMoO₄ luminescent thin films can be observed clearly.In Tb³⁺doped CaMoO₄/SrMoO₄:Eu³⁺thin films,the characteristic emission intensity of Eu³⁺firstly increases and then decreases with the increase of Tb³⁺doping concentration.In Eu³⁺doped CaMoO₄/SrMoO₄:Tb³⁺thin films,their emission colors can be tuned from green to red by increasing the Eu³⁺ doping concentration.Therefore,the optimal doping compositions are Ca_0.87MoO₄:Eu_0.1³⁺,Tb_0.03³⁺,Tb_0.03³⁺,Ca_0.90MoO₄:Tb_0.03³⁺,Eu_0.07³⁺,Sr_0.78MoO₄:Eu_0.15³⁺,Tb_0.07³⁺ and Sr_0.78MoO₄:Tb_0.15³⁺,Eu_0.07³⁺.The optical band gaps of the luminescent thin films are in the range of 4.49 to 4.72 eV.In addition,the crack-free thin films consist of dense nanoparticles.