Design,Preparation And Optical Properties Of Bi³⁺or Fe³⁺-doped Persistent Luminescence Materials

Persistent luminescence（Pers L）material can absorb and store irradiation energy in traps,and then emits light at a slow rate varying from a few seconds to several days after ceasing the excitation source,which can be compared to an optical battery.Owing to its irreplaceable advantages of“in-situ excitation-free”,long-lived luminescence time,autofluorescence-free,etc.,Pers L materials have recently evoked tremendous interest in the emerging technology fields of biomedicine,optical information storage,round-the-clock photocatalytic hydrogen,and so on.However,there are still many problems that need to be resolved,including the shortage of Pers L materials in the ultraviolet（UV）region,the limitation of emitters for near-infrared（NIR）Pers L materials,and the choice of the excitation mode.To overcome the aforementioned problems,in this dissertation,a series of Bi³⁺or Fe³⁺-activated UV and NIR Pers L materials were designed and developed by carefully selecting germanate and gallate compounds rich in a predetermined defect structure as matrix materials.Meanwhile,rechargeable and sunlight-activated UV-Visible-NIR Pers L material was also obtained.The crystal structure,fundamental optical properties of these materials as well as the trapping and de-trapping processes,and the trap characteristics are comprehensively surveyed by utilizing diversified characterization methods and density functional theory calculation,revealing the underlying Pers L mechanism of the developed materials.The main contents and research results are as follows:（1）By judiciously selecting the host and emitter,a new type of UVA Pers L material Li Sc Ge O₄:Bi³⁺with intense and ultralong Pers L was prepared.It was unraveled that the octahedral distortion caused by the occupation of heterovalent Bi³⁺ion for the Li site of Li Sc Ge O₄ host is an important factor for achieving UV Pers L,owing to the generation of abundant defects as effective trap center to participate in the Pers L process.Because of the existence of numerous carriers frozen in the deep traps after 10 h of Pers L decay,the as-prepared Li Sc Ge O₄:Bi³⁺exhibits enhanced photostimulated（PSL）UVA Pers L capabilities after illumination with the NIR laser for 30 s.Moreover,the regulation of emission wavelength and the improvement of the Pers L performance of Li Sc Ge O₄:Bi³⁺were realized through the cation substitution strategy.（2）By choosing the garnet structure compound Sr₃Y₂Ge₃O₁₂ with abundant cation sites as the matrix,a new kind of sunlight-activated UV-Visible-NIR Pers L material was reported by using Bi³⁺as the activation center.This material possesses a slow decay rate and is capable of experiencing an ultra-long Pers L duration time of longer than 60 h.It was found that this newly developed Pers L material can be effectively and repeatedly activated by sunlight radiation in various weather conditions because of its high response to both direct sunlight and diffuse solar radiation.Owing to the presence of stabilized deep traps with appropriate depths,Sr₃Y₂Ge₃O₁₂:Bi³⁺also exhibits outstanding PSL properties,which can be effectively activated by household LED or NIR laser after long-term decay.It was revealed that electron model and tunneling mechanism play roles in sunlight-activated and ultra-long Pers L of Sr₃Y₂Ge₃O₁₂:Bi³⁺.In addition,remarkable mechanoluminescence also can be found in this material.By utilizing the unique Pers L and PSL properties,we successfully demonstrated the applications of the Sr₃Y₂Ge₃O₁₂:Bi³⁺phosphor for night-vision signage and optical information storage.（3）A series of nontoxic Fe³⁺-activated NIR Pers L materials based on the MGa O₂（M=Li,Na）hosts were developed.These materials show a broad Pers L band peaked at around 750nm,which is longer than the emission wavelength of most reported NIR Pers L materials based on Cr³⁺emitters,and a higher penetration depth can be realized.Moreover,MGa O₂:Fe³⁺（M=Li,Na）possesses an ultra-long Pers L duration time of longer than 26 h,indicating that Fe³⁺can be a considerable candidate for activator ions to address the toxicity issue of chromium ions.More importantly,it was found that these materials are sensitive to the soft X-ray light source,which can be repeatedly charged to fill the trap,realizing renewable NIR Pers L of Fe³⁺without tissue penetration depth limitation.After terminating the X-ray light source,our material can obtain comparable Pers L performance to the typical Zn Ga₂O₄:Cr³⁺NIR Pers L material,which is likely due to the simple electronic structure of lithium that allows more effective photoelectric ionization to occur.（4）A new class of Fe³⁺-doped NIR Pers L material was designed by selecting the near inverse spinel configuration compound Mg Ga₂O₄ with heterovalent cations occupying the same crystallographic position.Based on the design concept of defect engineering,we propose a new strategy of defect enrichment for the activation of the NIR Pers L of Fe³⁺.The optical analysis and the calculation of density functional theory unraveled that the near inverse spinel structure of Mg Ga₂O₄ plays a critical role in the modulation of local electronic environments.The near inverse spinel structure can lower the carrier transfer barriers to accelerate the formation of carrier trap states within the bandgap.Therefore,more numerous defects in this structure may participate in the trapping and de-trapping process by comparison with the normal spinel configuration,resulting in excellent Pers L performance.