C. Gibbons

Engineering phosphors for field emission displays

Factors affecting the synthesis and properties of a new generation of fine particle low voltage phosphors in field emission displays are reviewed. The morphology and particle size, the composition and stoichiometry, the stability, together with the nature and shape of the particle surface, all play important roles in the performance of the final phosphor. Initial new results from novel synthetic methodology are presented and discussed. Their implications in the light of the known literature point the way to the successful conclusion of the current thrust of phosphor research for good red, green, and blue low voltage, high definition phosphors.

SUBMICRON-SIZED SPHERICAL YTTRIUM OXIDE BASED PHOSPHORS PREPARED BY SUPERCRITICAL CO2-ASSISTED AEROSOLIZATION AND PYROLYSIS

The synthesis of Eu(III)- and Tb(III)-doped yttrium oxide phosphor powders by supercritical CO2-assisted aerosolization and pyrolysis (at 1010 °C) from aqueous solutions of Y(NO3)3, Eu(NO3)3, and Tb(NO3)3 is presented. Dense, submicron aerosols are formed by contacting aqueous solutions of the precursor metal nitrates with supercritical CO2 at 1500 psi, and decompressing the mixture through a restrictor nozzle into a heated tube. X-ray diffraction data indicate that the powders are crystalline, and consist of a single phase. Scanning electron microscope shows that they are spherical in morphology and less than 1 μm in size with average diameters of ∼0.2 μm. The cathodoluminescence intensity of the Y1.91Eu0.09O3 powders, annealed at 1200 °C for 1 h, is more than twice greater than that of the industrial standard (P56, 3–10 μm in diameter) phosphor. The phosphors synthesized by this method are promising candidates for use in high-resolution low-voltage flat panel displays.

4.3: Factors Affecting Efficiency in Submicron Phosphors: Implications for Screens for High Definition Displays

Studies on phosphor particles in the range 0.05 to 0.35µm prepared from spherical particle precursors provide strong evidence that the main factors affecting light output are crystallinity, orientation, of the crystallite, and space between particles (in close packed arrays). These findings should be applicable to all high resolution phosphors.

39.1: Invited Paper: Submicron Spherical Phosphors for FED Applications

New synthetic routes using controlled precipitation and firing have led to the preparation of submicron phosphors. In this way, fine particle (0.25–0.5μm) phosphors have been prepared. These compare favourably to present industrial phosphors (3–8μm) with respect to efficiency and brightness at low voltage (300–5000V). The work is now being extended to oxides and binary and ternary sulphides, with considerable promise, although further optimisation is still required.

49.1: Improved Zinc-Sulfide-Type Phosphors by a Novel Synthetic Method

A novel, quick, and “clean”, method has been developed for the preparation of zinc sulfide phosphors for CRT and FED applications. The method involves the addition of a solution of sulfur in hydrazine monohydrate to a zinc salt solution, which results in precipitation of zinc sulfide, Firing this material has resulted in bright, efficient phosphors with improved luminescent properties between 500–15,000 eV, particularly for copper and silver activated ZnS.

The mechanism of light output from a phosphor thin film at low voltage

Studies of the cathodoluminescent light output of phosphor thin films excited by a low energy electron beam, of the order of 1keV, show that the light output is distributed throughout the film thickness of up to 2μm. It is concluded that the origin of the light cannot be directly related to the loss of energy of the incident electrons but must arise from some secondary process.

New blue‐emitting phosphor thin films for FEDs

Although considerable progress has been made in the investigation of blue-emitting phosphors for CRT application, there have been very few challenges to replace zinc sulfide silver. This phosphor, with which efficiencies of greater than 20% can be obtained, limited the effort invested in other blue systems. The need for low voltage, as well as other high-loading phosphors, however, pointed to a change of emphasis. The sulfide systems were not stable under these conditions and only P47, yttrium silicate cerium, has been used, with limited success. We felt that the narrow-band Eu 2+ phosphors would not yield the efficiencies required. At the University of Greenwich, a systematic investigation into refractory oxide phosphors using other rare-earth or transition-metal activators was thus initiated. These were directed at the preparation of powder and thin-film phosphor systems. The work reported here is on the synthesis and properties of thin films.