KLuS 2 single crystal samples undoped and doped with a small (five %) or large (38 %) focus of trivalent thulium or ytterbium ions were being synthesized in the form of thin hexagonal plates. The very low phonon Electrical power (�?20 cm ⁻�?) was verified making use of Raman spectroscopy. Samples were researched also by making use of optical