Photoluminescence And Temperature Sensing And WLED Applications Of Doped Modified Double Perovskites

In recent years,the study of optoelectronic properties of organic-inorganic and all-inorganic lead halide perovskite materials has become a hot spot in current materials science and physics research.Because of its excellent optoelectronic properties such as strong optical absorption,narrow full width at half maximum,high photoluminescence(PL)efficiency and tunable emission wavelength,it has attracted many researchers to study and discuss its performance improvement and practical application.According to the excellent optoelectronic properties of lead halide perovskite,researchers have prepared high-efficiency solar thin-film cells;based on its excellent optical gain and high PL efficiency,high-quality lead-based perovskite lasers have been successfully prepared;using its tunable emission wavelength to package white LED(WLED)devices,etc.However,the environmental instability of lead halide perovskite devices seriously affects their commercial application.Due to the presence of lead-containing elements,the toxicity of lead halide perovskites especially affects brain development.How to replace the lead element in lead halide perovskite on the basis of maintaining the original optoelectronic properties is a direction for scientific researchers.In recent years,a class of perovskite derivatives,double perovskites,has gradually attracted attention.Double perovskite has the characteristics of extremely high environmental stability and no toxic elements,and has become one of the alternative options for lead-based perovskite devices.Double perovskites can be divided into two structures,A₂B(IV)X₆ and A₂B(I)B(III)X₆.Due to less research on A₂B(IV)X₆,the structure of Cs₂SnCl₆and Rb₂SnCl₆ are used as the research subject.The low luminescence quantum efficiency of double perovskite Cs₂SnCl₆ and Rb₂SnCl₆ limits its commercial application.Therefore,in this paper,element doping modification is used to adjust the band gap width and emission mechanism of Cs₂SnCl₆and Rb₂SnCl₆ crystallites,so as to improve the luminescence quantum efficiency of Cs₂SnCl₆ and Rb₂SnCl₆ microcrystals(MCs).The PL applications and temperature sensing properties of Cs₂SnCl₆ and Rb₂SnCl₆ MCs are also studied according to the emission characteristics.Mainly divided into the following two tasks:Dual emission at 485 nm and 650 nm is achieved by simultaneously doping Bi³⁺and Sb³⁺ions into Cs₂SnCl₆ MCs by using a solvothermal method.In the process of preparation,adjusting the feeding ratio of Bi and Sb ions can realize the control of bimodal emission under the condition of keeping the feeding of other elements unchanged.Bi³⁺and Sb³⁺co-doped Cs₂SnCl₆ MCs can achieve dual emission at 485 nm and 650 nm under the irradiation of a 405 nm CW laser.Through temperature dependent PL spectra combined with time-resolved PL spectra,the blue emission at 485 nm is derived from[Bi _Sn+V_Cl]as the emission center,while the red emission at 650 nm is derived from self-trapped excitons(STEs).After grinding the Cs₂SnCl₆ MCs synthesized by controlling the feeding ratio of Bi³⁺and Sb³⁺,it is coated on the LED chip that can radiate 380 nm excitation light,and the WLED device is prepared and showed good stability.After the temperature dependent time-resolved spectra measurements,the fluorescence lifetime at485 nm is found to decrease linearly with the increase of temperature by fitting the decay curve.The temperature sensing properties of Bi³⁺and Sb³⁺co-doped Cs₂SnCl₆ are explored based on the variation of fluorescence lifetime with temperature.The maximum absolute sensitivity(S_A)and the maximum relative sensitivity(S_R)obtained by fitting calculation are 5.11 ns·K^-1 and 3.82%K^-1.Such good temperature sensing parameters prove that this material is suitable for 290-390 K temperature measurement.Double perovskite Rb₂SnCl₆ MCs have also become one of the alternative materials for lead halide perovskites due to their lack of lead toxicity and good stability.Te⁴⁺are doped into Rb₂SnCl₆ MCs by the solvothermal method.Under the irradiation of 405 nm CW laser,the PL peak of Rb₂Sn_0.95Te_0.05Cl₆ MCs is at 560 nm,and the photoluminescence quantum yield(PLQY)can reach 60%.The 560 nm emission is attributed to STEs according to the temperature-dependent PL spectra and time resolved PL spectra.In the fitting of the temperature dependent time-resolved spectra,it is found that the fluorescence lifetime at 560 nm shows a strictly monotonically decreasing trend with the increase in temperature.In terms of temperature sensing characteristics,the time-resolved spectra of Rb₂Sn_0.95Te_0.05Cl₆ MCs are collected for multiple cycles of 100-400 K.After fitting the decay curve,it is found that the fluorescence lifetime remains the same at each temperature.The maximum values of S_Rand S_A can reach 4.4%K^-1 and 28.23 ns·K^-1,respectively,showing excellent application potential in temperature sensing.The powder of Rb₂Sn_0.95Te_0.05Cl₆ MCs and silica gel have been coated with an LED chip that can emit430 nm excitation light.By adjusting the magnitude of the current,the LED can be modulated from cool to warm white light,and the repeatable modulation can be achieved.Rb₂Sn_0.95Te_0.05Cl₆ MCs show good temperature sensing and WLED application prospects.