For example Red = 660 nanometers = 1.8 electron-Volts = 1.8 Volts, which is the typical operating voltage for a Red LED.
Blue = 470 nm = 3.3 eV = 3.3 Volts operating voltage.
So: Deep UV (270 nm) is supposed to operate on ~4.6 Volts.
But article mentions 13.8 Volts. I wonder why there is such a huge gap?
I'm spitballing here, but I'd guess that the difference is due to a resistive drop across one or both of the contact layers.
In the article, Fig 2 says that they have 0.5A flowing with a pulse width of 50 ns and a pulse rate of 2 kHz. Their duty cycle is then 1/10000, so that's a lot of current flowing during the active part of the cycle. I haven't found all the details about the dimensions and doping, but any small amount of resistance might cause enough potential drop between the contact and the lasing region to account for the difference (especially that side contact to the bottom n-type layer.)
Furthermore, they need a fairly large current (0.4 A) to get this thing to lase. The "knee" in the U-I curve is at around 9 V and 0.05 A, so there seems to be a fair bit of voltage drop due to internal resistance of the device. This is probably also why they have to pulse the laser with a 0.01 % duty cycle in order not to produce too much heat.
I recall that you sometimes want to pump your atoms in a higher energy state than the one that corresponds to the output energy, but I forgot its usefulness. Could someone enlighten me on this? Or is it just for optically pumped mediums (thus pumped with higher energy photons than the emitted ones)?