Preparation,luminescence Properties And Application Of Lead-free Inorganic Halide Perovskites

Lead halide perovskites have emerged as superstar semiconductors owing to their superior optoelectronic properties.However,the issues of chemical and thermodynamic instability,and toxicity are yet to be resolved.Therefore,the development of high efficiency and stability of new non-lead all inorganic halide perovskite has important basic and practical significance.In this thesis,vacancy ordered A₂BX₆ non-lead inorganic halide perovskite fluorescent materials were selected for analysis,mainly studying the preparation,luminescence characteristics and application of Bi³⁺,Te⁴⁺,Sb³⁺and Mo⁶⁺doped vacancy ordered A₂BX₆ luminescent materials.At the same time,different ion doping was used to accurately control the spectral region from visible to near infrared of the vacancy ordered A₂BX₆ structure luminescent materials.The main contents of this thesis are as follows:1.For the tri-color of perovskite,the photoluminescence quantum efficiency（PLQE）of blue emission lags severely behind those of green and red ones.Besides,the excitations of the perovskite phosphors are usually in short ultraviolet wavelength range,which are not suitable for the commercial light-emitting diode（LED）chips.aliovalent doping and surface grafting-directed design of lead-free,stable,and high-efficient blue-emitting Cs₂Zr Cl₆ perovskite derivative were successfully prepared.Most remarkable achievements are the successful extending of excitation to match with the commercial NUV-LED chips and the boosting of quantum efficiency to be 50%through deliberate aliovalent doping with Bi³⁺.The blue emission～456 nm is firmly verified to originate from Bi³⁺ionoluminescence.The competition of harvesting electrons by STEs and Bi³⁺are studied in detail by steady-and transient-state fluorescence,combined with theoretical calculations.Surface grafting endows Cs₂Zr Cl₆:Bi³⁺with a robust water-resistant core-shell like structure and abiding emission.Surprisingly,the emission intensity even increases to 115.94%of the initial level after immersing in water for2 h.The ionoluminescent phosphor enables the fabrication of warm white LEDs together with common green and red phosphors on a commercial NUV-LED chip.It promotes the step toward development of lead-free,stable,low cost,and high-efficient perovskite derivatives for the next-generation warm white light solid-state lightings.This work not only promotes the material design of novel high performance perovskite derivative phosphors,but also the construction and revealing of structure-PL relationship.2.The use of LED lighting resulted in prolonged exposure to blue radiation,which is harm for human eye-health.Herein,a new strategy striving for“human-centric”lighting is demonstrated by doping Te⁴⁺into Cs₂Hf Cl₆,leading to a zero blue radiation through mixing red and green phosphors in a NUV-LED chip.Cs₂Hf Cl₆:Te is yielding an efficient yellow emission bright with a high photoluminescence quantum efficiency of 95.26%.Most surprising is the emission intensity maintains 96%of its initial strength even the post-annealing temperatue as high as to 450°C,demonstrating a superior thermal resistance.Moreover,excellent environmental stability was achieved via using silane coupling agent to modify the surface,and the broadband yellow emission intensity still remains 91%of the initial strength after soaking in water for 100 min,and hardly changes after 120 h of storage in air.A packaging device by using 395 nm LED chip,Cs₂Hf Cl₆:0.5%Te,green and red-emitting phosphor produces a warm white light with a high color rendering index while significantly and elimination of the blue radiation.These results demonstrate that Cs₂Hf Cl₆:Te perovskite is a promising phosphor with a capability of advancing human-centric lighting.3.Lead-free metal halide double perovskites（MHDPs）are recognized as one of the most promising alternatives to LHPs.Therefore,the development of novel lead-free broadband NIR emitting MHDP with high efficiency and robust stability is a great challenge of theoretical and practical significance.In this work,combining the temperature-programmed morphology evolution and unconventional high-temperature post-annealing,a lead-free,stable,and high-efficient broadband NIR emitting MHDP Cs₂Sn Cl₄Br₂ activated by Sb³⁺with the largest FWHM=164 nm was successfully synthesized.The morphology and particle size were evolved controllably to regular truncated hexagonal dipyramid,resulting in radically enhanced NIR emission intensity.Furthermore,we took the bull by the horns and used a high temperature post-annealing method to significantly improve the photophysical properties and physical stability.The NIR PLQY was 13-fold boosted.Excellent UV,water and ambient storage stability has also been demonstrated.The origin of NIR emission from Sb³⁺ionoluminescence was verified via the combination of experimental study and DFT calculations.Finally,as a proof-of-concept,we successfully used the as-obtained MHDP to fabricate a broadband NIR light emitting diode with radiant flux of 17.23 m W,portending NIR spectroscopy applications.This work will inspire the exploration of novel broadband NIR lead-free halide perovskites with superior stability for widespread NIR spectroscopy applications.4.NIR spectroscopy has been proved to be a reliable non-destructive analysis technique for qualitative and quantitative control of food and plants.In this work,combined with high temperature post annealing,a lead-free,stable and high-efficient broadband（1200～1650 nm）NIR emitting Cs₂Sn Cl₆ activated by Mo⁶⁺with the largest FWHM=202.55 nm was successfully synthesized,which matching well with the overtones of molecular vibrations in fruit components at 6500-7200 cm^-1.It provides light source support for the establishment of nondestructive detection method for quantitative analysis of fruit and meat water content.In addition,the luminescent properties and physical stability of Cs₂Sn Cl₆:Mo were improved by high temperature annealing.When the annealing temperature reaches 250°C,the emission intensity increases by 30%.And essentially no decay after soaking in water for 3 h.Taking a1mm apple slices as an example,the change of transmitted light intensity under different water content was studied by heating apple slices at an 80°C constant temperature.These results indicate that ultra-wideband NIR emission of Cs₂Sn Cl₆:Mo phosphor has potential application prospect and can be used for nondestructive food moisture analysis.