The presented work gives an overview of recent advances in research and development of novel phosphors based on Eu²⁺-doped K_xNa_1-xLuS₂ ternary sulfides which may be used as phosphors in white LED sources with tunable color correlated temperature. Tunability is achieved by using two different kinds of excitation diodes (nearUV and blue) in combination with the proper K/Na ratio in K_xNa_1-xLuS₂:Eu²⁺ structure. Intense photoluminescence due to the Eu²⁺ 5d – 4f allowed transition covers a broad emission region in visible range under both nearUV (~390 nm) and blue (~450 nm) excitations. The possibility to change the intensity ratio of the excitation diodes yields the changes of the output color correlated temperature. These changes are clearly demonstrated by shifts in the CIE color space; light quality is also quantified and discussed using CRI (color rendering index) and CQS (color quality scale) metrics [1].

However, to fully understand the Eu²⁺ emission mechanisms in these sulfidic hosts and to be able to optimize phosphor preparation and its performance, additional experimental techniques are applied to characterize these K_xNa_1-xLuS₂:Eu²⁺ phosphors. When a focused electron beam impinges on a cathodoluminescent (CL) material in a scanning electron microscope (SEM), secondary electrons, characteristic x-rays and visible photons are emitted. These signals can be used to construct a two-dimensional topographical, chemical and luminescence map, respectively [2]. Furthermore, thermal quenching and quantum efficiency measurements of K_xNa_1-xLuS₂:Eu²⁺ phosphors will be discussed for the first time.

1. V. Jarý, L. Havlák, J. Bárta, M. Rejman, A. Bystřický, Ch. Dujardin, G. Ledoux, M. Nikl. Circadian Light Source Based on K_xNa_1-xLuS₂:Eu²⁺ Phosphor. ECS Journal of Solid State Science and Technology, 7 (1), R3182-R3188, (2018). doi: 10.1149/2.0231801jss.
2. L.I.D.J. Martin, D. Poelman, P.F. Smet, J.J. Joos, Microscopic Study of Dopant Distribution in Europium Doped SrGa₂S₄: Impact on Thermal Quenching and Phosphor Performance. ECS Journal of Solid State Science and Technology, 7 (1) R3052-R3056 (2018). doi: 10.1149/2.0341709jss.