The Study Of Temperature Dependence Of The Optical Properties For Colloidal Pbse Quantum Dots

Compared with the traditional luminescent materials, Colloidal quantum dots haveexcellent optical properties, and have became a research hotspot recent years. So far,Colloidal quantum dots, both in the theoretical studies and in the preparation oflight-emitting devices have been got many important research achievements. The key issueson colloidal quantum dots include: synthesis and characterization of colloidal quantum dots;the impact of environment (eg temperature) on quantum dots; the luminescence properties ofquantum dots.Use the commonly used colloidal chemical synthesis method to synthetize various sizesof PbSe Colloidal quantum dots. In order to prepare better monodisperse quantum dots,thereaction requires a single, temporally short nucleation event followed by slower growth onthe existing nuclei.In the synthesis process in order to ensure that the environment ofanaerobic and anhydrous, Reagent preparation and follow-up treatment before reaction werecarried out in the glove box, and the synthesis reaction occurs in Schlenk system. Use thespectrometer to detect the absorption and PL spectra of quantum dots of various sizes. Allthose above will establish the experimental basis for the subsequent theoretical studies.Experimental studies have shown that the band gap of the quantum dots is sizedependent. For quantum dots of the same material, when the size decreases, the location ofthe spectral peak is blue-shift. Compared with the bulk materials, Carrieries in the quantumdot have additional limited energy as they are bound in a smaller space and lost freedom. Toresearch the limited energy in quantum dots, a spherical finite depth potential well modelwas established, the carrier in the potential well of the quantum dot surface or at the interface,considering that the carrieries are limited in the potential well of the quantum dot surface andinterface. Solve the Schrodinger equation of the potential well model and we will get thewave function and energy eigenvalue that is the limited energy. Coulomb effect between theelectrons and holes will be regarded as a perturbation. Band gap of core-shell quantum dotscan be solved by the same method, and the effect of quantum shell and the outside solutionon the nuclear carrieries were treated as the double potential well model.The band gap of the quantum dots is also temperature dependent. The relationship withtemperature is more complex, which is related with both material and size of the quantumdots. Experimental studies have shown that some materials are bule shift and others are redshift with the increase of temperature. We studied the temperature dependence of narrowband gap semiconductors PbSe, PbS,etc. The experimental results show that the band gap ofPbSe, PbS quantum dots in the large size range is blue shift, while in the small size range isred shift. Between the two regions there is a critical dimension that the band gap remainunchanged with the temperature change. Comprehensive consideration to the various factorsaffect the temperature dependence of the quantum dot band gap, we found that latticedilation effect and the interband electron-phonon effect are positive, and envelope thermal expansion, coulomb interaction, intraband electron phonon effect are negative. The actiondegree of the two effects is different in different size range, eventually leading to theemergence of the critical point of the temperature coefficient.FWHM (Full width at the half-maximum) is related to the size distribution of quantumdots. While the lattice thermal vibration in quantum dots makes the electrons exchangeenergy with the lattice atoms when excited by the excitation light which makes the Spectralbroadened. If the lattice thermal vibrational was quantized into a phonon, and that can betreated as a lattice phonon-electron scattering.The light-emitting efficiency of quantum dots is related to the rate of radiativetransition,and nonradiative transition. The formation of radiative transition,and nonradiativetransition can be attributed to lattice relaxation and multi-phonon transition theory,and wecan use the configuration coordinate diagram theory for qualitative explanation. Taking intoaccount the various factors that affect the efficiency of quantum dot light-emitting rate, theformula for calculating the luminous efficiency of colloid quantum dots can be derived,which can demonstrated the effects of various factors on the luminescence efficiency in acertain extent.