A Study on Some Questions of Luminescence in Nano Materials

Abstract: In a past few years, there is a considerable interest in the nano materials fieldsbecause of the unique physical chemical property. Particularly, the luminescence innano materials becomes a significant study direction of the nano materials field,which also have a good prospect of application and practical value in our daily lifeand even Hi-Tech fields. This thesis is based on the Supervisor's National NaturalScience Foundation of China "a relevant study of the new mechanism on lasing inrandom media "and " nonlinear effects at the low light levels ",We have studied manykinds of questions of luminescence in nano materials such as ZnO nano powder andquantum dot materials. The key points of this thesis are presented as follows:Summarize the fundamental property, optical characteristics and the tendency ofnano materials.Based on the experimental phenomena of lasing in ZnO nano powder, thesystem of interaction of ZnO nano powder media with matching pump light is treatedas a whole, and found a corresponding physical model. The localized mode spectrumand the eigen mode spectrum different direction of ZnO nano powder laser issimulated by means of transfer matrix method. As a result,the localized modes of therandom laser is correlative with not only pumping frequency and pumped area, butalso the incident direction of pump light.Based on the numeral simulation, the resultis the same as experimentation. In order to control the random laser, a new ideal ispresented in which the ZnO film should be inserted in a ordered medium. We designthe laser model of a kind of simple structure to output the characteristic to imitate andcalculate their laser properties, the result indicates the design is feasible, it provides areference to exploit UV laser.We study the laser of a single quantum dot in the extreme situation of nanomaterials. The system's optical characteristics of quantum dot coupled to a singlemode of an optical microcavity are studied with the numerical calculation methods. Itis shown that the threshold of the single quantum dot lasers is small under the function of the incoherent pumping. The steady output of the lasers is achievedquickly. When the coupling strength between quantum dot and cavity is larger, thethreshold is smaller and the steady output of the lasers is achieved more quickly. Thecurves of the decay rate and the laser levels tend towards saturation, which show thatthe changes of curves are related to the coupling strength, the quantum dot and themode of the optical cavity. A new research focus on the laser of quantum dot is theoutput of the single photon laser. It is a hotspot in single photon laser output of singleatom fields. In our research group, we have made the light field reach to the singlephoton amount grade by using quantum interference in atom and filed non-linearinteraction system. Because the single quantum dot called "a big artificial atom" havestrong coupling coefficient and controlled easier, we could make our study on theeffect of quantum interference in atom and filed non-linear interaction system expandto quantum dot and field non-linear interaction system, and then release the output ofthe single quantum dot and single photon. As a preliminary preparation of quantumdot and field non-linear interaction system, we study the quantum interference effectsof a Quasi-A-type four-level atom system with two light fields, some meaningfulphysical phenomena are found, which could offer a feasible scheme which makingfiled fall down to the grade of single photon in quantum dot and field non-linearinteraction system…
Key words: Nano materials; ZnO; Quantum dot; Luminescence; Quantum interference

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