Synthesis and Luminescence Properties of Green-to-Red Color-Tunable Upconverting K2Gd(PO4)(WO4):Yb3+,Tb3+,Eu3+ Phosphors

Scientists are increasingly interested in new inorganic luminescence materials that could be excited with near-infrared (NIR) radiation. These materials can be used as luminescent thermometers, bio-imaging agents, anti-counterfeiting pigments, etc. In this manuscript, we report the synthesis and investigation of optical properties of two series of K2Gd(PO4)(WO4):20%Tb3+ (KGPW): the first, KGPW:20%Tb3+ doped with 1–20% Eu3+, and the second, KGPW:10%Yb3+,20%Tb3+ doped with 1–20% Eu3+. The phase-pure specimens were prepared using a solid-state synthesis method. Down-shifting and upconversion luminescence studies have been performed using 340 and 980 nm excitation, respectively. For upconversion emission luminescence, Yb3+ ions were used as sensitizers in the KGPW phosphors. In these phosphors, Yb3+ ions absorb the 980 nm radiation and transfer the energy to Tb3+ ions. At his point, Tb3+ ions either emit themselves or transfer part or all of their energy to Eu3+ ions. It was observed that the emission color of the synthesized phosphors could be successfully tuned from the green to red by varying the Tb/Eu concentration ratio regardless of the 340 or 980 nm excitation. Such color change proves that one luminescent material (KGPW) can provide three colors (i.e., green, orange, and red). Herein, the optical properties, such as reflection, down-shifting excitation and emission spectra, upconversion emission spectra, fluorescence lifetime, thermal quenching, color coordinates, and quantum efficiency, were studied using steady-state and kinetic spectroscopy

Optical Properties Investigation of Upconverting K₂Gd(PO₄)(WO₄):20%Yb³⁺,Tm³⁺ Phosphors

Nowadays, scientists are interested in inorganic luminescence materials that can be excited with UV or NIR radiation and emit in the visible range. Such inorganic materials can be successfully used as luminescent or anti-counterfeiting pigments. In this work, we report the synthesis and optical properties investigation of solely Tm3+ doped and Yb3+/Tm3+ co-doped K2Gd(PO4)(WO4) phosphors. The single-phase samples were prepared using a solid-state reaction method. The Tm3+ concentration was changed from 0.5% to 5%. Downshifting and upconversion emission studies were performed under 360 nm and 980 nm excitation, respectively. Yb3+ ions were used as sensitizers in the K2Gd(PO4)(WO4) phosphors to transfer the captured energy to Tm3+ ions. It turned out that under UV excitation, phosphors emitted in the blue spectral area regardless of the presence or absence of Yb3+. However, a very strong deep-red (~800 nm) emission was observed when Yb3+ and Tm3+-containing samples were excited with a 980 nm wavelength laser. It is interesting that the highest upconversion emission in the UV/Visible range was achieved for 20% Yb3+, 0.5% Tm3+ doped sample, whereas the sample co-doped with 20% Yb3+, 2% Tm3+ showed the most intensive UC emission band in the NIR range. The materials were characterized using powder X-ray diffraction and scanning electron microscopy. Optical properties were studied using steady-state and kinetic downshifting and upconversion photoluminescence spectroscopy

Luminescence and Luminescence Quenching of K₂Bi(PO₄)(MoO₄):Eu³⁺ Phosphors with Efficiencies Close to Unity

A very good light emitting diode (LED) phosphor must have strong absorption, high quantum efficiency, high color purity, and high quenching temperature. Our synthesized K₂Bi­(PO₄)­(MoO₄):Eu³⁺ phosphors possess all of the mentioned properties. The excitation of these phosphors with the near-UV or blue radiation results in a bright red luminescence dominated by the ⁵D₀ → ⁷F₂ transition at ∼615 nm. Color coordinates are very stable when changing Eu³⁺ concentration or temperature in the range of 77–500 K. Furthermore, samples doped with 50% and 75% Eu³⁺ showed quantum efficiencies close to 100% which is a huge benefit for practical application. Temperature dependent luminescence measurements showed that phosphor performance increases with increasing Eu³⁺ concentration. K₂Eu­(PO₄)­(MoO₄) sample at 400 K lost only 20% of the initial intensity at 77 K and would lose half of the intensity only at 578 K. Besides, the ceramic disks with thicknesses of 0.33 and 0.89 mm were prepared from K₂Eu­(PO₄)­(MoO₄) powder, and it turned out that they efficiently converted the radiation of 375 nm LED to the red light. The conversion of 400 nm LED radiation to the red light was not complete; thus, the light sources with various tints of purple color were obtained. The combination of ceramic disks with 455 nm LED yielded the light sources with tints of blue color due to the low absorption of ceramic disk in this spectral range. In addition, these phosphors possess a very unique emission spectra; thus, they could also be applied in luminescent security pigments

Temperature-Dependent Luminescence of Red-Emitting Ba2Y5B5O17: Eu3+ Phosphors with Efficiencies Close to Unity for Near-UV LEDs

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Optical Properties of Red-Emitting Rb2Bi(PO4)(MoO4):Eu3+ Powders and Ceramics with High Quantum Efficiency for White LEDs

There are several key requirements that a very good LED phosphor should meet, i.e., strong absorption, high quantum efficiency, high colour purity, and high luminescence quenching temperature. The reported Rb2Bi(PO4)(MoO4):Eu3+ phosphors have all these properties. The Rb2Bi(PO4)(MoO4):Eu3+ phosphors emit bright red light if excited with near-UV radiation. The calculated colour coordinates show good stability in the 77–500 K temperature range. Moreover, sample doped with 50% Eu3+ possesses quantum efficiency close to unity. Besides the powder samples, ceramic disks of Rb2Eu(PO4)(MoO4) specimen were also prepared, and the red light sources from these disks in combination with near-UV emitting LED were fabricated. The obtained results indicated that ceramic disks efficiently absorb the emission of 375 and 400 nm LED and could be applied as a red component in phosphor-converted white LEDs

Luminescence and luminescence quenching of K₂ Bi(PO₄)(MoO₄ ):Sm³⁺ phosphors for horticultural and general lighting applications

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