Synthesis And Photoluminescence Properties Of Oxide Red Phosphors

At present,people are increasingly concerned about energy saving and environmental protection,but lighting consumes a large proportion of electrical energy.Light-emitting diodes（LEDs）have outstanding advantages such as:energy saving,low cost,long life and easy integration.Current red phosphors are mainly involved in two applications:white light LEDs and the preparation of plant growth LEDs.Firstly,white light is currently achieved by excitation of Y₃Al₅O₁₂:Ce³⁺(YAG:Ce³⁺)yellow phosphors with blue chips,but the lack of a red component leads to a low colour rendering index（CRI）and a high correlated colour temperature（CCT）,which does not meet the demand for high quality indoor lighting.The excitation of tri-color（red,green and blue）phosphors by near-ultraviolet chips enables the production of white light with a high colour rendering index and tunable colour temperature.Therefore,the development of red phosphors that can be efficiently excited by near-ultraviolet chips to obtain high-quality white light has become a research priority.Furthermore,as plants cannot grow and develop without light,not all light can be absorbed by plant.Two styles phytochrome,P_R and P_FR,absorb light at 660 and 730 nm,respectively,and it is therefore of interest to investigate phosphors that emit red and deep red light.The main focus of this thesis is the synthesis of highly efficient and stable red phosphors using a high temperature solid-state method by selecting suitable doping substrates.Specifically,highly efficient Eu³⁺doped red phosphors for the preparation of high colour rendering index warm white LEDs and highly efficient Mn⁴⁺doped deep red phosphors for plant growth LEDs.The main findings for the above problems are as follows:（1）A series of Ca₂LaHf₂Al₃O₁₂:Eu³⁺red phosphors were successfully prepared by a high temperature solid-phase method.In this work,the phase morphology,elemental composition,crystal structure and luminescence properties of the phosphors were investigated.The Ca₂LaHf₂Al₃O₁₂:Eu³⁺phosphor emits red light with a peaking of 614 nm under excitation with 394 nm light,and the optimum doping concentration of Eu³⁺is 50 mol%.The optimal sample,Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺,exhibits a high internal quantum efficiency（64%）and good thermal stability（the emission intensity at 423 K can be maintained at 73.7%of the room temperature emission intensity）.A warm white LEDs device was prepared by applying Ca₂LaHf₂Al₃O₁₂:50%Eu³⁺red phosphor,exhibiting warm white light（3853 K）with a high colour rendering index（88.3）.These results show that Ca₂LaHf₂Al₃O₁₂:Eu³⁺red phosphors can be applied in the preparation of warm white LEDs with high colour rendering index.（2）A serious of CaMg₂La₂W₂O₁₂:Mn⁴⁺(CMLW:Mn⁴⁺)deep red phosphors were successfully prepared by high temperature solid-state method.In this work,we studied the phosphor phase,crystal structure,morphology,elemental composition and optical properties,and finally its application in plant growth LEDs was studied.Excited by 352 nm light,these CMLW:Mn⁴⁺phosphors emitted bright deep red light with a peak emission of 708 nm.The optimum doping concentration of Mn⁴⁺was 0.8 mol%.The optimal CMLW:0.8%Mn⁴⁺phosphor exhibited high internal quantum efficiency（44%）and high color purity（99.37%）.Finally,CMLW:0.8%Mn⁴⁺phosphor was excited by blue chip to produce a plant-lighting LEDs device,which can emit a mixture of high brightness blue and deep red light.These results indicate that CMLW:Mn⁴⁺deep red phosphor can be used as a deep red phosphor for the preparation of plant growth LEDs.（3）A serious of Sr₂LuTa O₆:Mn⁴⁺(SLT:Mn⁴⁺)deep red phosphors were prepared by high temperature solid-state method.In this study,the phase,crystal structure and optical properties of SLT:Mn⁴⁺phosphors were studied.These SLT:Mn⁴⁺phosphors exhibitted deep red emission with a peak emission of 686 nm when excited by 346 nm light.The optimum doping concentration of Mn⁴⁺was 0.4 mol%.The quenching mechanism was the electric dipole-dipole interaction between adjacent Mn⁴⁺ions.Optimal SLT:0.4%Mn⁴⁺phosphor exhibitted internal quantum efficiency of 37%and color purity of 99.3%.In addition,SLT:0.4%Mn⁴⁺phosphor also showed good color stability.These results indicate that SLT:Mn⁴⁺deep red phosphor can be used in the preparation of plant growth LEDs.