NOVELTY - Holmium-ytterbium double-doped potassium lithium niobate single crystal, prepared from ytterbium oxide, holmium oxide, niobium oxide, lithium carbonate and potassium carbonate, is claimed. The molar ratio of ytterbium oxide and holmium oxide is 1:0.5-8. The molar ratio of ytterbium oxide and niobium oxide is 1:1263-1428. The molar ratio of ytterbium oxide and lithium carbonate is 1:571-637. The molar ratio of ytterbium oxide and potassium carbonate is 1:857-957.    USE - The holmium-ytterbium double-doped potassium lithium niobate single crystal is useful in: short wavelength and frequency upconversion solid-state lasers and solar cells; color displays; and biometrics.    ADVANTAGE - The potassium lithium niobate single crystal solves the problem that there is no material with frequency upconversion properties and also lithium potassium niobate as matrix.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for preparing the holmium-ytterbium double-doped potassium lithium niobate single crystal, comprising (a) weighing the ytterbium oxide, holmium oxide, niobium oxide, lithium carbonate and the potassium carbonate, uniformly mixing, adding the mixture into an agate mortar and grinding for 2-4 hours to obtain the mixed powder; (b) providing anhydrous ethanol, which has a volume-mass ratio with mixed powder of 2 ml:5 g, adding half of the anhydrous ethanol into the mixed powder, grinding the mixture in the agate mortar until the anhydrous ethanol is volatilized, adding the remaining half of anhydrous ethanol into the mixed powder, and grinding the mixture in the agate mortar until the anhydrous ethanol is volatilized to obtain crystallization powder raw material; (c) adding the crystallization powder raw material to a platinum crucible, placing the platinum crucible in a crystal growth furnace, heating the crystal growth furnace to 940-980 degrees C at a heating rate of 60-150 degrees C per hour and maintaining this temperature for 4-8 hours to obtain polycrystalline potassium lithium niobate; (d) heating the furnace to 1330-1380 degrees C at a heating rate of 60-150 degrees C per hour and maintaining this temperature for 4-8 hours, and cooling the mixture to 1295-1310 degrees C at a cooling rate of 20-80 degrees C per hour to obtain uniform melt; and (e) cooling the uniform melt to 1250-1270 degrees C, annealing and cooling again to room temperature at a cooling rate of 0.5-1 degrees C per hour or cooling the uniform melt at a constant cooling rate of 0.5-1 degrees C per hour for 0.5-1 hour.