Modulation Of Photoluminescence By Lattice Local Symmetry Of Mn²⁺ Doped CsPb(Cl_1-xBr_x)₃ Nanocrystals

Through exploring the doping conditions,the semiconductor nanocrystals are magnetically doped to form the distribution of micro or even single magnetic atoms,and to control the interaction between excitons and embedded magnetic atoms,which is the key to the preparation of multi-functional spin optoelectronic materials such as spin electronics,optoelectronics and so on.In recent years,metal halide perovskite semiconductor materials provide a new research carrier for magnetic semiconductor field.Through the halide anion exchange process,the band gap and the corresponding luminescent color of the perovskite NCs can be precisely controlled,while maintaining its high quantum yield(PLQYs)and nanocrystalline morphology.Mn²⁺doped Cs Pb(Cl_1-xBr_x)₃NCs has a dual wavelength emission characteristic.It consists of a wide orange color light emitted by the transition from the excited state(⁴T₁)of doped Mn²⁺to its ground state(⁶A₁)and a narrow emission tunable by the exciton in semiconductor NCs.In the energy level diagram,the emission of Mn²⁺is caused by the energy transfer(K_ET)from perovskite exciton energy band to the Mn²⁺excited state,and its intensity depends on the competition of exciton compound K_ehand K_ET rate.In order to further study the energy conversion mechanism,luminescence dynamics mechanism and spin mechanism of materials,Mn²⁺doped Cs Pb(Cl_1-xBr_x)₃NCs samples with different Cl/Br atomic ratios were synthesized;Temperature dependent photoluminescence(PL)test system,time-resolved PL system and pulse magnetic field PL measurements were conducted.The results of temperature change show that the energy transfer process is still continuous and enhanced at low temperature,which is caused by the strong d-d coupling between neighboring Mn²⁺ions;At low temperature and external magnetic-fields,Mn²⁺doped Cs Pb Cl₃ NCs perovskite shows circular polarizated emission related to the spin-polarization of excitions.In addition,by substituting different Cl/Br anions around the Mn site,the local field symmetry and band gap energy could be modulated,and the spin-polarized emission is found to be stabilized at close to room temperature.It is found that the polarized excited states and spin is determined by the asymmetry of crystal field and effect could be modulated,which is valuable for their future applications in spin-photonics.