Preparation And Properties Of Rare Earth Ion-activated Oxygenate Luminescent Materials

Due to their wide range of applications,luminescent materials have attracted extensive attention from researchers.Separate application requirements can be met by changing the type,concentration and matrix materials of the activating ions.Rare earth ions are usually chosen as activators because of their unique electronic structure and rich energy level transitions,which exhibit many spectroscopic properties advantages such as high color purity and brightness,high light absorption and conversion efficiency,resistance to high temperatures and high energy radiation,and fluorescent lifetime range from nanoseconds to milliseconds.Rare earth luminescent materials have become an important part of human life.As a new generation of solid-state lighting,white light-emitting diodes（w-LEDs）possess advantages such as high efficiency,energy-saving and environmental-friendliness.The traditional scheme for w-LEDs is to combine Ga N chips emitting blue light with cerium-doped YAG yellow phosphors,but this scheme has a lot of problems such as insufficient color rendering index.To address such issues,there are two solutions:on one hand,red phosphors that can be effectively excited by blue light can be added,and on the other hand,more efficient UV-LED can be utilized to realize white light emission.Therefore,the study of red phosphors that can be effectively excited by blue light and red-green-blue trichromatic phosphors that can be effectively excited by UV light has important theoretical and practical significance in improving color rendering index and enhancing white light emission.In this study,luminescent materials containing rare earth ions doped in oxygen-containing salts were synthesized using high temperature solid-state method,and their luminescent properties were investigated.The specific work is as follows:（1）Sr₂CeO₄:Eu³⁺luminescent material was prepared,and the influence of Eu3+substitution for Sr²⁺on the structure,luminescence,and lifetime was studied.Fluorescent powder Sr₂CeO4:Eu³⁺was synthesized by high temperature solid-state method,and the optimal synthesis condition was 1100℃for 30 h with no phase change caused by Eu³⁺doping.The excitation spectrum of the fluorescent powder Sr₂CeO₄:Eu³⁺had highest peaks at 279 nm,465 nm,and 530 nm and an emission peak at 612 nm,which can be used as red phosphors for UV-LED and blue-light LED.The optimal doping concentration of Eu³⁺in Sr_2-xCeO₄:x Eu³⁺was 5at%,which is commensurate with the quenching concentration of 5 at%with a critical distance of Rc=22.16（?）.First-principles calculations showed that the increase of the photoluminescence quantum yield after doping was due to the enhancement of the exciton binding energy caused by the increase of the effective number of electrons and holes,and the increase of Eu³⁺ion amount enlarged the band gap of Sr₂CeO₄.The photoluminescence mechanism of Sr₂CeO₄:Eu³⁺can be attributed to the energy transfer model and the defect conditions in the crystal.（2）A series of BaCeO₃powders co-doped with Eu³⁺,Eu²⁺,and Tb³⁺were synthesized and their structure and photoluminescent properties were studied.The fluorescent powder exhibits a cubic crystal system with a Pm3m space group.Ce³⁺and Ba²⁺ions occupy octahedral（CeO₆）and cubic dodecahedral(Ba O₁₂)environments,respectively,where Ba²⁺ions are drawn by the shared Ce⁴⁺octahedral network.The emission peak of BaCeO₃:Eu³⁺fluorescent powder is placed at 615 nm,making it suitable for red fluorescent powder in UV-leveraging and blue LED.BaCeO₃:Eu²⁺fluorescent powder has a wide and strong excitation and emission Spectrum.BaCeO₃:Tb³⁺can shift the emission color of the fluorescent powder from blue to cyan and then to green.Therefore,fluorescent powder BaCeO₃:Tb³⁺can be invoked as a tunable fluorescent powder from blue to green for UV LED.（3）A series of CsAlSi₂O₆fluorescent powders co-doped with Eu²⁺and Tb³⁺were synthesized and their structure and photoluminescent properties were studied.CsAlSi₂O₆:Eu²⁺、Tb³⁺are aluminum silicate compounds with a cubic crystal system and a space group of Ia3d.Each Cs⁺ion is dovetailed with 12 oxygen atoms,and the three-dimensional rigid framework is composed of（Al/Si）O₄tetrahedra units.CsAlSi₂O₆:Eu²⁺fluorescent powder has a wide and strong excitation and emission spectrum.The emission color of Cs_0.95-xAl Si₂O₆:0.05Eu²⁺、x Tb³⁺（x=0.01-0.18）fluorescent powder can be tuned from blue to cyan and then to green.The dipole-dipole interaction is the cause of the concentration quenching of CsAlSi₂O₆:Eu²⁺and CsAlSi₂O₆:Tb³⁺.Fluorescent powders CsAlSi₂O₆:Eu²⁺and Tb³⁺can be invoked as blue-green fluorescent powders for UV LED.