The event happened on May 1, 2013 at the United States Patent and Trademark Office's National Inventors Hall of Fame. From the Invent.Org website:
"In the mid-1960s, Don Bitzer and Gene Slottow, faculty at the University of Illinois at Urbana-Champaign, and graduate student Robert Willson, worked together to create the first plasma display. A new display was needed for the PLATO computerized learning system that had been created by Bitzer because traditional displays had no inherent memory, lacked high brightness and contrast, and flickered. Today, plasma displays are known for their accurate color reproduction, high contrast ratios, wide viewing angle and large screen refresh rates."
Here's a video Don recorded for the NIHF, answering the question about PLATO's relationship to NSF and its funding: