The article does not explain what they use, but it seems to imply that there is no fluorescent conversion layer and the white light comes directly from the LED.

That could be done if the LED actually contains a multiple structure combining red, green and blue LEDs, but in the past such a combined LED had the disadvantage that in time the efficiency of the 3 components degraded at a different rate, which resulted in a color shift.

For now, the luminous efficiency of this LED is quite poor, unsuitable for lighting but only for indicator LEDs or display applications, but they claim that for such small LEDs even the traditional LEDs had poor efficiency and they hope to improve the efficiency later to more acceptable levels.