Abstract
Eu-doped ternary sulfides of general formula ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y) are presented as a novel interesting material family which may find usage as X-ray phosphors or solid state white light emitting diode (LED) lighting. Samples were synthesized in the form of transparent crystalline hexagonal platelets by chemical reaction under the flow of hydrogen sulfide. Their physical properties were investigated by means of X-ray diffraction, time-resolved photoluminescence spectroscopy, electron paramagnetic resonance, and X-ray excited fluorescence. Corresponding characteristics, including absorption, radioluminescence, photoluminescence excitation and emission spectra, and decay kinetics curves, were measured and evaluated in a broad temperature range (8–800 K). Calculations including quantum local crystal field potential and spin-Hamiltonian for a paramagnetic particle in D3d local symmetry and phenomenological model dealing with excited state dynamics were performed to explain the experimentally observed features. Based on the results, an energy diagram of lanthanide energy levels in KLuS2 is proposed. Color model xy-coordinates are used to compare effects of dopants on the resulting spectrum. The application potential of the mentioned compounds in the field of white LED solid state lighting or X-ray phosphors is thoroughly discussed.
Highlights
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo, cathodo- and electroluminescent applications [1]
The current work presents a new family of optical materials, namely Eu-doped ternary sulfides ALnS2 (A = Na, K, Rb; Ln = La, Gd, Lu, Y), as pot1e7ntially interesting for solid state lighting and X-ray phosphors applications
Characteristic 5D0-7Fx emission lines in the 570–730 nm spectral region attributed to Eu3+ appeared under X-ray, UV and VIS excitation at low temperatures in Eu-doped KLuS2, KYS2, KGdS2, RbLuS2 and NaLuS2
Summary
Sulfide-based luminescent materials have attracted a lot of attention for a wide range of photo-, cathodo- and electroluminescent applications [1]. The lack of a bright blue phosphor to produce the third primary color was a key issue in the realization of full-color thin-film electroluminescent (FCTFE) displays until the breakthrough discovery of alkaline earth thiogallate thin films. In the 1990s, a saturated green electroluminescence was obtained with thin sputtered films of Eu2+-doped SrGa2S4 [2] and a deep blue one was achieved with Ce3+-doped SrGa2S4 and CaGa2S4 thin films [3,4]. A laser effect was observed in rare earth (RE)-doped calcium thiogallate crystals. CaGa2S4:Ce3+ can be used as a gamma ray scintillator [7]. The highest light yield (LY) scintillating crystals are currently found among oxides ((Lu,Y)2SiO5:Ce,Ca LY = 32,000 ph/MeV [8], Gd3(Al,Ga)5O12:Ce, LY = 58,000 ph/MeV [9],
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