Investigation of ultrafast carrier dynamics in ZnO rods using two-photon emission and second harmonic generation microscopy

The demand for novel optoelectronic and photonic technologies has fueled an intense research effort to synthesize and characterize nanostructured semiconductor materials with unique properties that lend themselves to technological innovation. Zinc Oxide has emerged as an attractive candidate for a variety of applications, due in part to a large second order nonlinear susceptibility, its wide band-gap and large exciton binding energy. We have used time-resolved nonlinear two-photon emission and second harmonic generation microscopy to characterize the optical properties and excited state dynamics of individual rods. Ultrafast emission microscopy is used to follow the trapping dynamics of photoexcited charge carriers. Our results show a time-dependent red-shift in the trap emission band that is interpreted as arising from carrier percolation through trap states. In a second series of experiments, second harmonic generation (SHG) microscopy illustrates the connection between the optical mode structure of the object and its nonlinear mixing efficiency. Images show a periodic modulation in the SHG efficiency that is symmetrically situated relative to the rod midpoint. This phenomenon arises when the fundamental optical field couples into standing wave resonator modes of the structure and is a direct manifestation of the tapered shape of the rod.

[1]  Bruce E. Gnade,et al.  Mechanisms behind green photoluminescence in ZnO phosphor powders , 1996 .

[2]  G. Yi,et al.  Time-resolved photoluminescence of the size-controlled ZnO nanorods , 2003 .

[3]  S. Rakshit,et al.  Trap-state dynamics in visible-light-emitting ZnO:MgO nanocrystals , 2008 .

[4]  Brian P. Mehl,et al.  Direct imaging of optical cavity modes in ZnO rods using second harmonic generation microscopy. , 2010, The journal of physical chemistry. A.

[5]  Allen Taflove,et al.  Computational Electrodynamics the Finite-Difference Time-Domain Method , 1995 .

[6]  Detlef W. Bahnemann,et al.  Preparation and Characterization of Quantum Size Zinc Oxide: A Detailed Spectroscopic Study. , 1987 .

[7]  E. Irene.  Electronic Materials Science , 2005 .

[8]  W. Webb,et al.  Nonlinear magic: multiphoton microscopy in the biosciences , 2003, Nature Biotechnology.

[9]  Richard D. Schaller,et al.  Near-Field Imaging of Nonlinear Optical Mixing in Single Zinc Oxide Nanowires , 2002 .

[10]  H. Cao,et al.  Large enhancement of second harmonic generation in polymer films by microcavities , 1999 .

[11]  A. Fiore,et al.  Phase matching using an isotropic nonlinear optical material , 1998, Nature.

[12]  Marius Grundmann,et al.  Whispering gallery modes in nanosized dielectric resonators with hexagonal cross section. , 2004, Physical review letters.

[13]  I. Carusotto,et al.  RESONANT SECOND HARMONIC GENERATION IN ZNSE BULK MICROCAVITY , 1999 .

[14]  Joseph T Hupp,et al.  ZnO nanotube based dye-sensitized solar cells. , 2007, Nano letters.

[15]  H. Gerritsen,et al.  Exciton polaritons confined in a ZnO nanowire cavity. , 2006, Physical review letters.

[16]  C. Simonneau,et al.  Second-harmonic generation in a doubly resonant semiconductor microcavity. , 1997, Optics letters.

[17]  Steven G. Johnson,et al.  Improving accuracy by subpixel smoothing in the finite-difference time domain. , 2006, Optics letters.

[18]  G. D. Boyd,et al.  Resonant optical second harmonic generation and mixing , 1966 .

[19]  J. Wiersig.  Hexagonal dielectric resonators and microcrystal lasers , 2002, physics/0210052.

[20]  Takafumi Yao,et al.  Correlation between grain size and optical properties in zinc oxide thin films , 2002 .

[21]  Marius Grundmann,et al.  Whispering gallery mode lasing in zinc oxide microwires , 2008 .

[22]  Yu Hang Leung,et al.  Optical properties of ZnO nanostructures. , 2006, Small.

[23]  Andries Meijerink,et al.  The Kinetics of the Radiative and Nonradiative Processes in Nanocrystalline ZnO Particles upon Photoexcitation , 2000 .

[24]  Ji-Yong Park,et al.  Identification of dispersion-dependent hexagonal cavity modes of an individual ZnO nanonail , 2008 .

[25]  H. Morkoç,et al.  A COMPREHENSIVE REVIEW OF ZNO MATERIALS AND DEVICES , 2005 .

[26]  E. Samulski,et al.  Synthesis of Variable‐Aspect‐Ratio, Single‐Crystalline ZnO Nanostructures. , 2006 .

[27]  J. DeSimone,et al.  Ultrafast excited-state energy migration dynamics in an efficient light-harvesting antenna polymer based on Ru(II) and Os(II) polypyridyl complexes. , 2001, Journal of the American Chemical Society.

[28]  Kam Sing Wong,et al.  Time-resolved photoluminescence study of a ZnO thin film grown on a (100) silicon substrate , 2003 .

[29]  E. Rosencher,et al.  Second‐harmonic generation in nonbirefringent semiconductor optical microcavities , 1995 .

[30]  V. Berger,et al.  Second-harmonic generation in monolithic cavities , 1997 .

[31]  Zhen Li,et al.  Structural and luminescent properties of ZnO nanorods prepared from aqueous solution , 2007 .

[32]  L. Schmidt‐Mende,et al.  ZnO - nanostructures, defects, and devices , 2007 .

[33]  Kelly P. Knutsen,et al.  Ultrafast Carrier Dynamics in Single ZnO Nanowire and Nanoribbon Lasers , 2004 .