Synthesis And Properties Of Bi³⁺-doped Yttrium Gallium Garnet Ultraviolet Persistent Phosphors

Persistent luminescence is a special optical phenomenon that certain materials can continuously exhibit light emission after removal of the excitation source,which involves an energy storage process under excitation and an energy release process after excitation.Benefitted by its delay emitting feature,persistent luminescence materials have been extensively investigated and widely used in various application fields,such as information storage,solar energy utilization,emergency lighting and signage,biological imaging,etc.However,in contrast to huge progress and achievement in visible and near-infrared persistent luminescence materials over the past two decades,the development of persistent materials in ultraviolet spectral region(200-400 nm)has been mightily constrained and hindered by limited host materials and emitting centers.Recently,considering features of short light wavelength,high photon energy,invisibility to the human eye,and self-sustained light emission,ultraviolet persistent materials hold important application potentials for photocatalysis,sterilization,imaging,anti-counterfeiting,and light-mediated theranostics,boosting the demand for novel ultraviolet persistent phosphors.Herein,through component regulation and preparation optimization,Y3Ga5O12:Bi3+and(Y,Gd)3Ga5O12:Bi3+ultraviolet persistent materials are successfully synthesized by introducing Bi-Cemitting center to yttrium gallium garnet hosts.The luminescence and defect properties are systematically investigated,and the relationship between defect levels and persistent luminescence is illustrated.By analyzing the process of energy storage,transfer and release,relevant luminescence schemes are constructed,and the persistent luminescence mechanism is revealed.The main work is discussed in detail as follows:(1)Through the high-temperature solid-phase method,Y3GaO12:Bi3+ persistent material is synthesized.After being illuminated by ultraviolet lights(240-400 nm),the material exhibits single-band ultraviolet persistent light emission,the excitation peaks are located at 250 nm,280 nm,300 nm,and 340 nm.Illumination of 254 nm UV lamp can induce ultraviolet B persistent luminescence peaking at 313 nm that lasts for 60 h.Moreover,Y3Ga5O12:Bi3+can also be effectively charged by sunlight at different times and in different weather.Minutes of sunlight irradiation can arouse persistent luminescence enduring for 12 h.Besides,the Y3Ga5O12:Bi3+material possesses excellent photostimulated persistent luminescence performance.The ultraviolet persistent luminescence of pre-irradiated sample by high energy UV light can be overtly strengthened by low energy light stimulation for several seconds or minutes.The electrons distribution and transfer process in persistent luminescence and photostimulated persistent luminescence are studied in detail by thermoluminescence analysis,and the ultraviolet persistent luminescence procedure is illuminated.Finally,on the utilization of the invisible feature to the human eye,long time self-sustained luminescence,and no-interference indoor environments,Y3Ga5O12:Bi3+material is used for indoor optical tagging application.(2)Narrowband ultraviolet B persistent luminescence material is successfully achieved by introducing Gd3+to yttrium gallium garnet and utilizing the persistent energy transfer from Bi3+ to Gd3+.The energy level diagram,together with the spectroscopic investigations verify the occurrence of energy transfer process.Upon high energy ultraviolet light irradiation,the emission spectrum of(Y,Gd)3Ga5O12:Bi3+material contains narrow band line emission attributing to 6P7/2→8S7/2 transition of Gd3+and band emission attributing to 3P0,1→1SO transition of Bi3+.The persistent luminescence excitation spectrum of(Y,Gd)3Ga5O12:Bi3+covers a broad spectral region from 240 to 380 nm,peaking at 255 nm,280 nm,300 nm and 340 nm,respectively.254 nm UV lamp and natural sunlight both can activate the persistent material and induce narrow band ultraviolet B persistent luminescence for more than 12 h.Furthermore,the effects of Gd introduction on defect level distribution and depth are investigated by thermoluminescence analysis,the electrons trapping and de-trapping process under excitation of 254 nm UV lamp and natural sunlight are both analyzed in detail.