1. Field of the Invention
The present invention relates to generally to phosphors and more specifically to the production of nanoparticulate phosphors.
2. Description of the Background Art
There is a resurgence in phosphor research due to the recent interest in developing emissive flat panel displays, e.g. full-color low-voltage field emitter displays (FEDs), large area plasma displays (PDs) and electroluminescent displays (ELDs). For example; to make low-voltage FEDs. decreasing the required electron energy by two orders of magnitude from the 30 KV range of CRTs while maintaining significant light output is quite challenging. In low-voltage FEDS, the incident electron mean free path in the phosphor is extremely short, and some researchers feel that the photon generation process should occur reasonably close to the electron-hole pair creation point to avoid non-radiative recombination at nearby defects. Furthermore, there is the belief that present day micron size phosphors are surrounded by a dead layer of defective material whose thickness is comparable to or greater than the mean free path of low energy electrons used in low voltage FEDs. The defects in this surface layer, which are produced, for example, by ball milling and other harsh surface (and bulk) defect producing processes, are believed to be non-radiative recombination centers. These result in low optical output when these phosphors are bombarded by low energy electrons.
Research interest in the general field of nanoscale materials has been growing fast. New methods of developing nanoparticles are being developed, and their novel physical properties are being studied. For example, in Yang et al. U.S. Ser. No. 08/841,957 filed Apr. 7, 1997. Now U.S. Pat. No. 6,106,609 nanocrystalline semiconductor particles are produced within the mesoporous cavities of a bicontinuous cubic phase. The cavities contain at least one of the reactants required to form the semiconductor compound. Any other required reactants are diffused into the mesoporous cavities.
Accordingly, it is an object of the present invention to provide phosphors having a high light output level.
It is another object of the present invention to provide nanocrystalline phosphors that have no or few bulk defects.
These and additional objects of the invention are accomplished by forming doped nanocrystalline semiconductor particles within the mesoporous cavities of a bicontinuous cubic phase. The cavities contain at least one of the reactants required to form the semiconductor compound. Any other required reactants are diffused into the mesoporous cavities. Doped nanocrystals are produced by diffusing dopant or activation ions into the mesoporous cavities along with the other reactants or by including dopant or activation ions within the mesoporous cavities of the BCP under conditions such that the nanoparticles are doped with an average of one or less dopant ions per particle. For the purposes of the present specification and claims, the words xe2x80x9cdopantxe2x80x9d and xe2x80x9cactivatorxe2x80x9d are used interchangeably to describe the ion that when placed within the interior of a nanocrystalline particle, provides the particles with phosphorescence.