Photoluminescence And Temperature Sensing Properties Of Na- And Bi-doped Inorganic Double Perovskites

In recent years,organic-inorganic hybrid halide perovskites have received much attention due to their widely tunable photoluminescence(PL),large absorption coefficient,high photoluminescence quantum yield(PLQY),and fast carrier mobility.Although some perovskite materials have made great progress in optoelectronic devices,the lead toxicity and the instability of lead-based materials have seriously hindered their commercial application.Researchers devote themselves to improve the properties of lead halide perovskite by doping or coating.Based on the basic structure of perovskite,various double perovskite has been synthesized,which are widely studied due to good thermal stability and the absence of lead elements.Lead-free double perovskite Cs₂Ag In Cl₆ has acquired much attention due to direct bandgap,long carrier lifetime,non-toxicity,and good stability.The PLQY of Cs₂Ag In Cl₆is relatively low due to intrinsic parity-forbidden transition.However,the octahedral coordination of Ag and In and the easy substitution of Ag and In by other elements demonstrate double perovskite Cs₂Ag In Cl₆is suitable for the host of different doped materials.Different doping can break the parity-forbidden transition,modify the bandgap,and finally improve the luminescence performance.The investigation on lead-free double perovskite can help us to explore the component control for novel lead-free perovskite.It is significant for improving luminescent performance and expanding application.A series of materials are prepared by the solvothermal method,and the basic structural and optical characterization are performed.In this dissertation,the properties of the PL emission mechanism are investigated.In addition,Cs₂Ag_0.6Na_0.4In Cl₆,Yb/Bi codoped Cs₂Ag_0.6Na_0.4In Cl₆,and Er/Bi codoped Cs₂Ag_0.6Na_0.4In Cl₆ MCs are selected as the research center.The PL mechanism and their performance as temperature sensors are explored.This dissertation mainly completes the following three aspects of research work.1.By turning the temperature and power,the steady-state PL and time-resolved photoluminescence(TRPL)properties of different Na doped Cs₂Ag_xNa_1-xIn Cl₆ are studied.Through fitting the relationship between PL intensity,full width at half maxima(fwhm),and temperature,the exciton binding energy,Huang Rhys factor(S),and other parameters of the experimental samples are obtained to study the luminescence mechanism of double perovskite materials.The broad-band luminescence of Cs₂Ag_xNa_1-xIn Cl₆ MCs is attributed to the self-trapped excitons(STEs).2.Cs₂Ag_0.6Na_0.4In Cl₆ has a wide spectrum and warm white emission.By introducing Yb³⁺into the white emission of Cs₂Ag_0.6Na_0.4In_0.9Bi_0.1Cl₆(CANIBC),visible and near-infrared luminescence can be observed simultaneously under 405nm continuous wave(CW)laser irradiation.We demonstrate that the energy transfer mechanism is the direct energy transfer from STEs to Yb³⁺emission.Then,due to different fluorescence quenching progress of STEs and Yb³⁺emission under variable temperature conditions,a temperature sensor based on fluorescence intensity ratio(FIR)is designed and the absolute sensitivity(S_a)and relative sensitivity(S_r)are required according to the ratio of different peak intensities.Based on FIR(985/635),we can realize the maximum S_a and S_r,which can reach 0.113 K^-1 and 1.66%K^-1.These good temperature sensing properties show that this material is very suitable for the sensor of 300-460 K.3.Er³⁺has abundant transition energy levels.By introducing Er³⁺into CANIBC,the emissions of STEs and Er³⁺(²H_11/2(530 nm),⁴S_3/2(555 nm),⁴F_9/2(660 nm))are realized.Similarly,temperature sensors(530/555,530/590,530/660)are designed based on FIR according to the different quenching rates of Er³⁺emission and STEs emission.The temperature sensing performance based on Er³⁺(530)and STEs is much better than that of Er³⁺(530/555,530/660).The maximum S_a and S_r of 530/590 can reach 0.098 K^-1 and1.69%K^-1,respectively.These properties demonstrate a better application prospect.