Plasma panel shines brighter than ever

22 Jan 2008

Philips is using an alternative green phosphor to achieve record levels of luminance in their plasma display panels.

“Increased efficacy and luminance can be achieved at a moderate voltage increase.”

A team from the Philips Research Laboratory in the Netherlands has fabricated plasma display panels (PDPs) with an efficacy of 5 lm/A and luminance of 5000 cd/m² at VGA resolution, and an efficacy of 4 lm/W and luminance of 3400 cd/m² at XGA resolution. Until now, PDP white light efficacy values of about 1.5 lm/W were typical. (Journal of Applied Physics 103 013301)

"The market for PDPs is expanding rapidly, however an improved PDP efficacy and a decreased cost are required to enhance market penetration," said Gerrit Oversluizen from the Philips Research Laboratories. "We found that by using an alternative green phosphor, a marked increase of efficacy and luminance can be achieved at a moderate voltage increase."

PDP efficacy is known to decrease at high luminance, due to both phosphor and plasma saturation. This is a particular issue for the green phosphor that is traditionally used in PDPs. "The default green phosphor, Willemite, is especially sensitive to saturation," said Oversluizen. "We found a Tb-activated Triborate green phosphor to be less sensitive. It combines high quantum efficiency and low saturation at high UV load."

What's more, the team found that adjusting the gas content of the panels decreased plasma saturation further, consequently increasing efficacy. A Xe-concentration of 50% was used by the group, compared with present-day commercial panels that typically apply a Xe-concentration of 4-5%.

The team fabricated 4-inch test panels composed of 256 columns and 48 rows with a conventional stripe-type barrier cell configuration, blasted in glass. According to the team, a stripe-type barrier structure is attractive because it is less alignment sensitive and allows the use of low-cost soda-lime glass.