Photoluminescence Regulation Of CsPbX₃ Quantum Dots Through Doping Mn²⁺,Yb³⁺ And Er³⁺

CsPbX₃（X=Cl,Br,I）perovskite quantum dots（PQDs）exhibit promising prospect for applications in perovskite solar cells,light-emitting diodes,lasers because of their tunable band gap,high photoluminescence quantum yield and simple synthesis process.However,they still suffer from the poor tunability of photoluminescence in visible range,lacking near-infrared（NIR）photoluminescence,and excitation range limit in ultraviolet-visible region,and their photoluminescence shows a small Stokes-shift and is easily affected by oxygen and temperature,hindering the development of their practical applications.Therefore,this dissertation aim to regulate the photoluminescence of CsPbX₃PQDs in visible and NIR region by doping Mn²⁺ions and Yb³⁺,Er³⁺ions.The effects of oxygen and temperature on the photoluminescence behavior were also investigated.Further,the NIR excited upconversion photoluminescence from Yb³⁺,Er³⁺ions doped CsPbX₃ PQDs has been observed and the underlying mechanism was dicussed.The main research contents are summarized as follows:To regulate the photoluminescence of CsPbCl₃ PQDs,the Mn²⁺ions were doped and the effect of oxygen on Mn²⁺emission was also investigated.The d-d transition photoluminescence of Mn²⁺ions（610 nm）with the Stokes-shift greater than 200 nm was realized in Mn²⁺doped CsPbCl₃ PQDs.And the generation of singlet oxygen was observed.Mn²⁺doped CsPbCl₃ PQDs were encapsulated by superhydrophobic silica and polystyrene materials to prevents them from disintegrating in aqueous medium and showing the singlet oxygen dominant process on degrading organic pollutant methyl orange,further verifying the generation of singlet oxygen.The singlet oxygen generation with quantum yield of 108%was achieved at Mn²⁺doping concentration of 15.6%,which is much higher than that of inorganic photo-sensitizer Cd Se（5%）.Combined the experimental results with atomic-level density functional theory（DFT）calculations,the efficient singlet oxygen generation was ascribed to a quantum-cutting process from an inner Mn²⁺excited energy level into two surface Mn²⁺-defect energy levels.To regulate the photoluminescence CsPbCl₃ PQDs in NIR region,the Yb³⁺and Er³⁺ions were co-doped and the underlaying mechanism of the effect of temperature on NIR photoluminescence were also investigated.The Yb³⁺ion emission（990 nm）and Er³⁺ion emission（1540nm）was realized through the quantum-cutting process of exciton-Yb³⁺and cascade energy transfer process of exciton-Yb³⁺-Er³⁺,separately.Thermal stable Yb³⁺emission and thermal enhanced Er³⁺emission（2.5-fold）were observed,which shows the advantages of longer luminescence wavelength and better thermal stability when compared with traditional Cr³⁺-based materials.Thermal stable Yb³⁺emission was ascribed to that energy transfer process occurs at sub-picosecond time scale faster than thermal quenching involved carrier trapping process.The temperature-dependent spectral measurements and water content dependent spectral measurements were conducted,revealing that thermal enhanced Er³⁺luminescence is mainly due to the minimizing quenching effect of surface adsorbed water molecules on Er³⁺⁴I_13/2state by temperature increase.Moreover,the Yb³⁺,Er³⁺:CsPbCl₃ PQDs fabricated NIR LED also showed inherited thermally enhanced properties.To realize the NIR excited upconversion luminescence in perovskite quantum dots,Er³⁺(or Yb³⁺)was singly doped into CsPbX₃ PQDs.The visible photoluminescence of 500 nm was observed from Yb³⁺doped CsPbCl₃ PQDs under976 nm excitation,which was verified as the cooperative luminescence of two Yb³⁺ions through the quadratic pump dependence and the comparison between the experimental emission spectra and the self-convolution spectra of two Yb³⁺ions.Further,Er³⁺sensitized upconverted exciton emission（444 nm）was achieved in CsPb(Br_0.33/Cl_0.67)₃ PQDs through doping Er³⁺ions with multi-energy levels.The band gap was tuned from 2.68 e V to 3.04 e V by adjusting the Br/Cl ratio and the tunable upconverted exciton photoluminescence ranging from 409nm to 464 nm was also realized.