Enhancement or quenching of QD, Q-wire and QW radiations

In the field of solid-state physics, enhancement or quenching of the radiation of QDs, Q-wires, and QW are methods used to reduce the radiative emission of quantum dots, wires and wells. Many methods have been developed to enhance or quench the radiation by adjusting the size, changing the structure, and adding other materials to the quantum structures. By doing these, the radiation patterns are regulated, which are expected to have the potential to lead to a new class of light sources. In this page, recent research on zinc oxide (ZnO) nanostructures is introduced and the principles of the enhancement and quenching in the structures are discussed.

ZnO quantum dots

The optical properties of ZnO quantum dots can be controlled by changing of the size.^[1] As the size of the ZnO nanocolloids increases, the absorbance increases, but optical band gap of the nanocolloids decreases. The third-order optical susceptibility increases with increasing particle size.

ZnO quantum wires

Radiation fields are changed by the methods to fabricate the quantum wires.^[2] Micro photoluminescence spectra of an individual suspended as-grown ZnO nanowire and an individual ZnO nanowire processed by sonication/dispersion procedure. The thickness of the nanowire tends to change the radiation fields. The thickness of the nanowire is also related to the peak wavelength. For the nanowire with regular shape shown, only slight difference in UV to visible emission ratios was observed for the two parts with different diameters. Correspondingly, UV emission peaks have almost the same position at 375.2 nm. On the other hands, for the nanowire with irregular shape and rougher surface, with the decrease of the diameter, dramatically increased green emission and decreased UV emission can be observed, which was accompanied by the red shift of the UV emission peak energy.

ZnO quantum wells

Radiation fields of ZnO quantum wells can be adjusted by coupling through localized surface plasmons. By sputtering Ag islands onto ZnO films, their band gap emission coming through the Ag island films was enhanced by threefolds, while the defect emission was quenched.^[3] The enhancement is mainly dependent on the Ag island size. photoluminescence spectra of seven samples which have different Ag island sizes are represented; #4 sample has the largest size of island, but # 1 sample has the smallest size of the island. It is revealed that sputtering time related to the island size have an effect on the enhancement of 380 nm band and 530 nm band. The PL enhancement or quenching may be due to the coupling of the light emission with the localized surface plasmon resonance of the Ag islands. When localized surface Plasmon resonance scattering dominates over the absorption process, the localized surface Plasmon energy can be recovered to free space emission, leading to the enhancement of light emission. Otherwise, light emission will be attenuated due to non-radiative dissipation of localized surface plasmon absorption.

References

1. Irimpan L, Krishnan Deepthy BA, Nampoori VPN, Radhakrishnan P (2008). "Size-dependent enhancement of nonlinear optical properties in nanocolloids of ZnO". Journal of Applied Physics. 103 (3): 033105. Bibcode:2008JAP...103c3105I. doi:10.1063/1.2838178.
2. Gao M, Li W, Liu Y, Li Q, Chem Q, Peng LM (2008). "Microphotoluminescence study of individual suspended ZnO nanowires". Applied Physics Letters. 92 (11): 113112. Bibcode:2008ApPhL..92k3112G. doi:10.1063/1.2898168.
3. Chen P, Li D, Yuan Z, Chen P, Yang D (2008). "Enhancement of ZnO light emission via coupling with localized surface plasmon of Ag island film". Applied Physics Letters. 92 (4): 041119. Bibcode:2008ApPhL..92d1119C. doi:10.1063/1.2839404.