Phosphor claims will be questioned at displays conference

17 Jun 2002

In a keynote address to the Electronic Information Display conference in London, in the UK, from 21 to 23 of next month, Jack Silver of the Centre for Phosphor and Display Materials, University of Greenwich, in London, will question much of the wisdom that is current in phosphor research for next-generation display devices.

Regarding the development of miniature cathode-ray tubes (CRTs), he will say that there seems to be no correlation, as had previously been thought, between particle size and brightness in powder phosphors. In fact, Greenwich has found that crystallinity, brought about by various synthetic processes, affects the brightness more than the particle size.

With field-emission displays (FEDs), it was previously thought that the addition of conducting powders to standard phosphors merely made the deposited screen more conductive. This is now being questioned.

Silver's address will point out that there is little agreement that phosphors can be used for FEDs. Some manufacturers claim that even minute traces of alkali metals cause instabilities, while others believe that sulphides contaminate the microtip emitters. Some scientists actually use sulphide phosphors in microtip devices and report an improved performance of low-voltage phosphors.

However, Silver will say that the improvements that have been reported so far have not yielded a practical low-voltage FED. Zinc oxide still remains the most efficient phosphor at low voltages, but little quantitative data is available on the actual maintenance characteristics of low-voltage phosphors under long-term operating conditions in a real display.

Turning to LEDs, Silver will stress that, although there has been much hype about using blue, green and red gallium nitride LEDs together to make cheap, efficient white light, it has now been recognized that there are serious problems. These include the fact that the three different LEDs may age at different rates, so that although the light starts out as white, it may deteriorate quickly. Silver will suggest that a combination of LEDs and phosphors may be a better long-term solution.