Optical Properties Of Manganese Doped Lead-free Perovskite

The unique photoelectric properties of all inorganic perovskite are closely related to its crystal structure and spatial dimension.In order to control the crystal structure,perovskite materials with different compositions are synthesized by ion substitution.In the study of spatial dimensions,the usual strategy is to synthesize zero-dimensional（0D）and two-dimensional（2D）perovskite materials by adjusting the size and chemical potential of A-site cations.These perovskite materials of different dimensions all show excellent optical properties.In addition,the transition metal Mn²⁺is introduced into halide perovskite in order to obtain ideal photophysical properties.In general,Mn²⁺luminescence results from the transition from the⁴T₁ excited state to the ⁶A₁ ground state.The wavelength position of the emission band depends on the crystal field environment.Mn²⁺with tetrahedral coordination usually emits green light,while Mn²⁺with octahedral coordination usually emits red light.Recent studies have found that the introduction of Mn²⁺not only produces multicolor emission,but also has been observed to activate afterglow emission of crystal.In this paper,Mn²⁺was successfully introduced into lead-free perovskite single crystals and nanocrystals by different synthesis methods to obtain lead-free perovskite materials with different dimensions and compositions,and their optical properties were systematically studied.The first chapter introduces some common growth methods of perovskite single crystals and nanocrystals,such as Bridgman and hydrothermal methods for single crystal synthesis,hot injection method,ligand-assisted reprecipitation method and reverse microemulsion method for nanocrystalline synthesis.In addition,this chapter describes the optical properties of Mn²⁺doped perovskite,including photochromism and photoluminescence.In Chapter 2,a transparent photochromic Cs₂Ag In Cl₆ perovskite single crystal was grown by hydrothermal reaction and its optical properties were characterized.The photochromism of single crystal was activated via a Mn²⁺-doping strategy,and both coloration and decoloration could be triggered by light at appropriate wavelengths,365 nm and 520 nm for example.Unlike heat-induced decoloration,the optical route represents a much faster tool to erase information.As a caveat from photochromism,the photoluminescence quantum yield（PL QY）was significantly decreased down to 1.7%.In an attempt to boost the quantum yield,sodium ions were introduced as a co-dopant.Surprisingly,the co-doping strategy not only boosted the PL QY to 33%,but also deactivated the photochromism.Our work expanded the library of photochromic materials by introducing a new perovskite single crystal,representing a paradigm for the making and breaking of photochromism.In Chapter 3,2D RP phase Mn-doped Cs₂Cd Cl₄ nanocrystals were synthesized via a room temperature reverse microemulsion method and their optical properties were characterized.By X-ray diffraction analysis and XRD analysis,the synthesized nanocrystals were confirmed to be pure phase.By controlling different amounts of oleic acid and observing by scanning electron microscope,it was found that different amounts of oleic acid can form different sizes of nanocrystals.The excitation and emission spectra of nanocrystals were obtained by steady-state spectrum test.The optimal excitation was 291 nm and the red emission of 590 nm was obtained,which was attributed to the ⁴T₁-⁶A₁ transition of Mn²⁺.The millisecond emission lifetime was obtained by the transient spectrum test,which further confirmed that the red emission originated from Mn²⁺.and a reasonable explanation of the luminescence mechanism was proposed.