Preparation And Properties Of Several New Rare Earth Luminescent Materials Doped With Bi³⁺ And Cr³⁺

Currently,phosphor-converted light-emitting diodes（pc-LED）have been widely used in lighting,display,night vision,non-destructive testing,and plant growth applications due to their high efficiency,energy saving,environmental protection,and low price.In pc-LED,light-emitting materials play an important role,so the development of high-performance rare-earth light-emitting materials is of great theoretical and practical significance.In this dissertation,we synthesized a series of new high-efficiency rare earth light-emitting materials doped with Bi³⁺and Cr³⁺,investigated their crystal structures and luminescence properties,and explored their applications in LEDs.The specific results are shown below:（1）Novel Ba₃YGa₂O_7.5:Bi³⁺,Eu³⁺luminescent materials have been synthesized to realize single-substrate white light emission by utilizing the energy transfer between Bi³⁺and Eu³⁺.Ba₃YGa₂O_7.5:Bi³⁺luminescent material can be efficiently excited by ultraviolet light,and its emission peak is located at 487 nm.Ba₃YGa₂O_7.5:Eu³⁺emits orange-red light at 590 nm.The modulation of the luminescence color from cyan to white to orange-red was achieved by adjusting the doping concentration of Eu3+.Finally,a single-substrate white LED with a CRI of 84.9 was prepared.（2）A series of BaSrGd₄O₈:Bi³⁺,Eu³⁺luminescent materials were synthesized,the emission peak of BaSrGd₄O₈:Bi³⁺was located at 465 nm,and time-resolved spectra showed the presence of two different Bi³⁺sites.The quantum efficiency was almost doubled by optimizing the flux doping type and doping level.The modulation of the luminescence color from blue to violet to red was achieved by exploiting the energy transfer between Bi³⁺and Eu³⁺.Finally,WLED devices with high CRI and low CCT were prepared.（3）Ba₂Gd Al O₅:Bi³⁺yellow luminescent material was synthesized with an emission peak located at 556 nm,a half peak width of 127 nm,an internal quantum yield of 82.78%,and thermal stability of 104.1%@423 K.Oxygen vacancies and Bi²⁺were identified as the cause of the traps by XPS,and the depth of the traps was measured to be 0.9 e V by using thermoluminescence spectroscopy.It was observed that the luminescent material exhibits photochromism under near-UV excitation and can be faded by high-temperature heat treatment.Finally,WLED devices with high color rendering index were obtained.（4）Single-doped multi-site La₄Ga₂O₉:Bi³⁺luminescent materials were synthesized.Changing the excitation wavelength position,the tunable luminescence from blue to red was realized.Properties such as site occupancy,fluorescence decay lifetime,and temperature-dependent spectroscopy were analyzed in detail,and pyroelectric spectroscopy showed that the resistance to thermal burst in the blue-light region was attributed to the compensation effect of the trap.The effects of doping concentration and excitation position on the optical thermometry performance at high temperatures are investigated,and it is found that the best thermometry results can be obtained with a doping concentration of 0.02 mol and an excitation position at 385 nm,with the Sr maximum of 3.969%K^-1.In addition,the multi-mode optical thermometry performance at low temperatures and fluorescence lifetimes are investigated separately,which indicates that La₄Ga₂O₉:Bi³⁺has excellent optical thermometry performance.（5）Sr₃Si Al₁₀O₂₀:Cr³⁺,Yb³⁺near-infrared luminescent materials have been synthesized.The optimal excitation position of Sr₃Si Al₁₀O₂₀:Cr³⁺is located at 408 nm with two emission centers,and the emission achieves a change from ultra-narrowband（FWHM=37 nm）to ultra-broadband（FWHM=225 nm）with the increase of Cr³⁺doping concentration.attributed to the presence of significant energy transfer between the two emission centers.By introducing Yb³⁺ions,the emission intensity of this phosphor was extended beyond 950 nm,the thermal stability was improved,and the energy transfer property was studied in detail.Finally,high-power near-infrared LEDs were prepared to explore the potential applications in night vision lighting,non-destructive monitoring,and information encryption.