無機化學特論 ( 四 )

1. 無機化學特論(四) 授課老師：林寬鋸 教授 http://web.nchu.edu.tw/pweb/users/kjlin

2. Advanced Inorganic Chemistry (IV): Material Chemistry • Overview of Solid State Chemistry (two weeks) • Synthesis methods in solid sate (three weeks) • Electronic conductivity (2 weeks) • Magnetic (2 weeks) • Electronic transfer and energy transfer (2 weeks) • Functional hybrid systems for biosensing (3 weeks)

3. Home works • Semiconductor quantum dots (q-dots) • Submitted q-dots you prefer (2/27) • Energy levels for q-dots (3/6) • Syntheses and characterizations (3/20) • Absorption and emission spectra (3/27, 4/10) • Electrical transport properties (4/17, 4/24) • Single electron tunneling (5/1) • Optical gain and Lasing (5/8) • Application in Bio-imaging (5/15, 5/22,) • Application in solar-cell (5/29) • Nanopartilces, core-shell colloidal, 1D-wires, 1D-arrangements

4. NANOCHEMISTRY • Nanochemistry is an active new field that deals with confinement of chemical reactions on nanometer length scale to produce chemical products that are of nanometer dimensions (generally in the range of 1-100nm). The challenge is to be able to use chemical approaches that would reproducibly provide a precise control of composition, size, and shape of the nano-objects formed. These nanomaterials exhibit new electronic, optical, and other physical properties that depend on their composition, size, and shape. Nanoscale chemistry also provides an opportunity to design and fabricate hierarchically built multilayer nanostructures to incorporate multifunctionality at nanoscale.

5. Nanochemistry offers the following capabilities: • Preparation of nanoparticles of a wide range of metals, semiconductors, glasses, and polymers • Preparation of multilayer, core-shell-type nanoparticles • Nanopatterning of surfaces, surface functionalization, and self-assembling of structures on this patterned template • Organization of nanoparticles into periodic or aperiodic functional structures • In situ fabrication of nanoscale probes, sensors, and devices

8. Nanotechnology for Biophotonics：Bionanophotonics • Nanophotonics is an emerging field that describes nanoscale optical science and technology. • the use of nanoparticles for optical bioimaging, optical diagnostics, and light-guided and activated therapy

9. two classes of nanoparticle emitters • (1) semiconductor nanoparticles, also known as quantum dots, whose luminescence wavelength is dependent on the size and the nature of the semiconductors. These nanoparticle emitters can be judiciously selected to cover the visible to the IR spectral range. They can also be surface-functionalized to be dispersable in biological media as well as to be conjugated to various biomolecules. • (2) up-converting nanophores comprised of rare-earth ions in a crystalline host.

11. Quantum Dots

12. Semiconductor Quantum Dots • Quantum dots (also frequently abbreviated as Qdots) are nanocrystals of semiconductors that exhibit quantum confinement effects, once their dimensions get smaller than a characteristic length, called the Bohr’s radius. • This Bohr’s radius is a specific property of an individual semiconductor and can be equated with the electron-hole distance in an exciton that might be formed in the bulk semiconductor. • For example, it is 2.5nm for CdS. Below this length scale the band gap (the gap between the electron occupied energy level, similar to HOMO, and the empty level, similar to LUMO) is size-dependent

13. Qdots • When the particle size decreases below the Bohr’s radius, the absorption and the emission wavelengths of the nanoparticles shift to a shorter wavelength (toward UV). • The quantum dots, therefore, offer themselves as fluorophores where the emission wavelength can be tuned by selecting appropriate-size nanocrystals. • By appropriate selection of the materials and the size of their nanocrystals, a wide spectral range of emission can be covered for biolimaging. • Also, a significantly broad range of emission covered by many sizes of nanocrystals of a given material can be excited at the same wavelength. The typical line widths are20-30nm, thus relatively narrow, which helps if one wants to use the quantum dots more effectively for multispectral imaging.

14. Qdots • Compared to organic fluorophores, the major advantages offered by quantum dots for bioimaging are: 1. Quantum dot emissions are considerably narrower compared to organic fluorophores, which exhibit broad emissions. Thus, the complication in simultaneous quantitative multichannel detection posed by cross-talks between different detection channels, derived from spectral overlap, is significantly reduced. 2. The lifetime of emission is longer (hundreds of nanoseconds) compared to that of organic fluorophores, thus allowing one to utilize time-gated detection to suppress autofluorescence, which has a considerably shorter lifetime. 3. The quantum dots do not readily photobleach. 4. They are not subject to microbial attack.

15. A major problem in the use of quantum dots for bioimaging is the reduced emission efficiency due to the high surface area of the nanocrystal. enhance the emission efficiency of the core quantum dot.

16. A B CdSe PbSe J. Phys. Chem. B, Vol. 106, No. 41, 2002 Partuicles size：3.5 nm J. Am. Chem. Soc.,Vol. 115.No. 19. 1993