Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having growth from a solution comprising a solvent which is...
Reexamination Certificate
1993-04-20
2001-06-05
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having growth from a solution comprising a solvent which is...
C117S073000, C117S075000, C117S956000
Reexamination Certificate
active
06241819
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This invention relates to semiconductor materials and particularly to quantum sized doped semiconductor particles and methodology for manufacturing these particles.
By making semiconductor particles small enough to show quantum confinement effects and doping them with a luminescent activator element (referred to as “doped nanocrystals”), new optical properties are created which differ from those of chemically identical bulk material and from the quantum confined host material alone. An activator doped and quantum confined host material was made (ZnS:Mn) that demonstrates blue shift in the excitation wavelengths of the activator for the first time. This new material characteristic indicates a fundamental change in optical properties and this is the first time a material exhibiting this characteristic has been made. Other methods to produce this material and other unique properties, such as rapid luminescent decay and reduced excitation voltages for flat panel cathode ray tubes, are also possible.
It has been recognized that when the radius of a semiconductor crystallite is near that of the Bohr radius of the exciton, there is a quantum size effect and its electronic properties change (Y. Wang and N. Herron, “Nanometer-Sized Semiconductor Clusters: Materials Synthesis, Quantum Size Effects and Photophysical Properties”, J. Phys. Chem. 95 525, 1991). This had been observed as a blue shift in the optical bandgap for quantum sized ZnS particles in solution (H. Weller, U. Koch, M. Guitierrez and A. Henglein, “Photochemistry of Colloidal Metal Sulfides. Absorption and Fluorescence of Extremely Small ZnS Particles (The World of Neglected Dimensions)”, Ber. Bunsenges. Phys. Chem. 88 649, 1984). Most of the II-VI and some III-V and group IV semiconductors have been prepared as quantum sized particles and demonstrate quantum size effects in their physical properties. The size at which the particles demonstrate changes in their bandgap from the quantum size effects vary with the intrinsic electronic structure of the compound but typically appear when below 100 Å in diameter. To exhibit quantum size effects it is also necessary for the particles to remain isolated from one another, if allowed to aggregate the material exhibits bulk properties despite the small size of the individual particles.
Quantum size particles have previously been prepared in several ways: spontaneous nucleation in solution, heterogeneous growth from a substrate material, growth within a micelle, growth in solution atop a carrier particle, nucleation in a sputtering chamber, and laser ablation. Undoped semiconductor particles of CdS which approach quantum size were prepared in a polymer matrix (See P. A. Bianconi et al “crystallization of an Inorganic Phase Controlled by a Polymer Matrix”, Nature 349, 315, 24 Jan. 1991). See also, Wang et al “Three-Dimensionally Confined Diluted Magnetic Semiconductor Clusters: Zn
1−x
M
x
S” Solid State Communications, Vol. 77, No. 1, pp. 33-38 (1991). The present invention is directed towards the doping of a quantum sized semiconductor host material with an activator element which demonstrates new material properties.
Possible applications for new materials based on the concepts and materials described in this application include:
Luminescent phosphors for use in cathode ray tubes and lights.
Thin films for electroluminescent displays.
Lasing phosphors.
The use of luminescent activators and magnetic particles for magneto-optical recording and displays.
Lower voltage phosphors for flat cathode ray tubes
Markers for medical diagnosis
The present application also provides methodology for manufacturing quantum sized doped semiconductor particles. The methodology is particularly advantageous in that it provides a relatively simple approach to the manufacture of doped quantum sized semiconductor particles at room temperature. Furthermore, the particles so produced are dispersed within a polymer matrix and the reaction which forms the doped particles takes place in the polymer matrix. Thereafter, the polymer matrix maintains the doped particles separate from one another so that they maintain their quantum physical effects without agglomeration.
In the methodology, a metal halide compound containing the metal ion component of the host particle is dissolved in a suitable solvent (such as water) with a metal halide of the dopant (activator). Also dissolved in the solvent is polyethylene oxide (PEO) which is thereafter cast onto a flat surface and dried. The polymer matrix is peeled off the flat surface, cut into coupons and immersed in a hydrocarbon solvent that does not react with the polymer matrix. Also dissolved in the hydrocarbon solvent is a compound which contains the other chemical component of the host needed to form the doped semiconductor particles. The reaction to create and grow the doped semiconductor crystals in the polymer matrix takes place over a period of time, from days to weeks, at room temperature. After the particle growth is complete, the polymer matrix is dried and quantum sized semiconductor doped particles are dispersed within the polymer matrix.
The doped nanocrystals produced by the present invention have a luminescent efficiency which is relatively high for films prepared at room temperature. Normally, thin films of bulk ZnS:Mn used in electroluminescent devices yield high efficiency when prepared above temperatures of 350° C. For powder phosphors, this temperature is frequently as high as 1000° C. However, high processing temperatures would change the morphology of quantum sized particles and destroy their properties. The new doped nanocrystals also emit light significantly faster (shorter luminescent decay time) than that observed with corresponding bulk material. This faster luminescent decay time in a nanocrystal provides advantage over bulk material for application where speed is important, i.e. faster phosphors for next generation TV's and displays. It is believed that this characteristic has not been observed before.
REFERENCES:
patent: 4974933 (1990-12-01), Ainslie et al.
patent: 5093286 (1992-03-01), Nogami et al.
patent: 5238607 (1993-08-01), Herron et al.
Wang et al “Three Dimensionally Confined Diluted Magnetic Semiconductor Clusters; Zn1MnxS”, Solid State Communications, vol. 77, No. 1 pp. 33-38 1991.*
“Crystallization of an Inorganic Phase Controlled by a Polyer Matrix” P.A. Bianconi et al, Nature, 349, 315 Jan. 25, 1991.
“Photochemistry of Colloidal Metal Sulfides . . . ” H. Weller et al, Ber. Bunsenges. Phys. Chem. 88 649 1984, month unknown.
“Nanometer-Sized Semiconductor Clusters: Materials Synthesis, Quantum Size Effects, and Photophysical Properties” Wang et al, Physical Chemistry, Jan. 24, 1991, No. 2.
Bhargava Rameshwar
Gallagher Dennis
Bartlett Ernestine C.
Kunemund Robert
North American Philips Corp.
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