Preparation And Application Of Vacancy-ordered Halide Double Perovskites Luminescent Materials

Lead-based perovskites have been extensively studied due to their outstanding optical properties,high photoluminescence quantum yields,easily tunable band gaps,and good carrier mobility.However,toxicity and stability have always been potential hazards for lead-based perovskites.Vacancy-ordered double perovskites are lead-based perovskites derived structural variants with similar properties to lead-based perovskites,making them excellent hosts for phosphors.At present,studies on ion doping to modulate the luminescence properties of vacancy-ordered double perovskites have been preliminary explored.The vacancy-ordered double perovskites are rich in species,and the luminescence regulation,luminescence mechanism,and stability of vacancy-ordered double perovskites need further research.Based on this,this thesis uses ns² ions as dopants to study the regulation mechanism of ns² ions on the luminescence properties of vacancy ordered double perovskites,further propose the corresponding luminescence mechanism,and explore the stability and practical application of the material.The details are as follows:（1）The ratio between[Hf Cl₆]^2-and[Te Cl₆]^2-in the Cs₂Hf_1-xTe_xCl₆ vacancy-ordered double perovskite was tuned by an ion-exchange strategy,which further regulated the crystal structure,luminescence properties and energy bands.Pure Cs₂Hf Cl₆ exhibits strong self-trapped excitons emission and direct bandgap structure,while pure Cs₂Te Cl₆ exhibits weak yellow light and indirect bandgap structure.In Cs₂Hf_1-xTe_xCl₆,as the concentration of Te⁴⁺ions increases,the self-trapped excitons emission of Cs₂Hf Cl₆ will be gradually quenched due to the change of exciton recombination channel.Theoretical calculations and solid lines reveal another highly efficient yellow self-trapped exciton recombination in Cs₂Hf_1-xTe_xCl₆.The optimal ratio of Cs₂Hf_0.99Te_0.01Cl₆ has a quantum efficiency of 83.46%and good stability,and two high-efficiency white light-emitting diodes are obtained by assembling them.The ion-exchange construction of Cs₂Hf_1-xTe_xCl₆ provides a new perspective for the design and regulation of vacancy-ordered double perovskite materials.（2）The Cs₂Hf Cl₆ vacancy-ordered double perovskite was doped with Bi³⁺ions to explore the effect of doping ions on the self-trapped excitons emission of the matrix.The³P₁→¹S₀ transition of Bi³⁺ions appeared in the system after Bi³⁺ion doping.With the increase of Bi³⁺concentration,the self-trapped excitons emission of the matrix and the electronic transition of Bi³⁺ions show a fierce competition.The optimized Bi³⁺doping concentration achieves a quantum efficiency of 69.08%,and the half-peak width of blue light emission is 64 nm.Furthermore,this efficient blue light emission exhibits excellent stability.The white light-emitting diodes assembled with commercial phosphors obtained a high color rendering index of 92.5.（3）Sb³⁺ion-doped Cs₂Zr Cl₆ luminescent material was synthesized by precipitation method.Cs₂Zr Cl₆:x%Sb³⁺includes two luminescent centers,self-trapped excitons emission of Cs₂Zr Cl₆ host and electronic transition of Sb³⁺.The ¹P₁→¹S₀ transition（singlet state）and the ³P₁→¹S₀ transition（triplet state）of Sb³⁺ion were further confirmed by wavelength-dependent spectroscopy and time-resolved fluorescence spectroscopy.The excitation wavelength-dependent tunable color change was obtained by adjusting the electronic transition of Sb³⁺and the self-trapped excitons emission of the Cs₂Zr Cl₆ matrix,and showed unique application value in the field of anti-counterfeiting,broadening the application scope of vacancy-ordered double perovskites.（4）Using ns² ions doped Rb₂Sn Cl₆ vacancy ordered double perovskite,the luminescence properties of ns²(Bi³⁺,Te⁴⁺and Sb³⁺)ions in the same host were systematically studied.The Rb₂Sn Cl₆ vacancy-ordered double perovskite does not emit light by itself,while broadband blue,yellow and red emission are obtained after Bi³⁺,Te⁴⁺and Sb³⁺ion doping,respectively.Combined with theoretical calculations,we find that these broadband emissions not only have the characteristic electronic transitions of ns² ions,but are also capable of exhibiting self-trapped excitons emission associated with metal halides.Based on the co-doping strategy,we obtained white light-emitting materials with excitation wavelength-dependent tuning of color temperature.This provides new insights into the application and regulation of luminescent properties of lead-free halide perovskites.