P2 was a long persistence phosphor. It was used in analog oscilloscopes because those couldn't be refreshed -- the waveform was drawn onto the display as it was

P2 was a long persistence phosphor. It was used in analog oscilloscopes because those couldn't be refreshed -- the waveform was drawn onto the display as it was received, and the phosphor was responsible for making that visible. You wouldn't want that in a computer monitor. The computer is perfectly capable of refreshing the monitor, and the long duration of the phosphor would make anything rapidly changing (like a scrolling display) impossible to read because all of the previous contents would interfere with the current image.