Highly Efficient and Thermally Stable Eu2+-Doped Ca9Nd(PO4)7 Phosphor for Near-Ultraviolet White-Emission LED Applications

Various Eu2+-based Ca9Nd(PO4)7 (CNP:xEu2+, with different x values) materials are prepared via facile solid-state reaction. Their crystal structures are investigated in detail by means of the Rietveld refinement. The structure of CNP:Eu2+ with a trigonal lattice is analogous to that of β-Ca3(PO4)2. Therefore, Eu2+ ions tend to incorporate calcium sites in the host. All the obtained samples can be excited using near ultraviolet (nUV) light to present blue-green emission. An optimal dopant concentration is verified at x = 0.8 with a large critical interaction radius (11.21 Å). The mechanism of the concentration quenching effect is assigned to the multipole-multipole interaction. CNP:xEu2+ possesses a short decay lifetime of ∼60 μs and can endure severe working conditions thanks to its great thermal stability. The relative photoluminescence (PL) intensity of CNP:0.8Eu2+ can retain 84.75% of the pristine intensity measured at room temperature, and the relative intensity remains as high as 69.97% at 423 K. The CNP:Eu2+ phosphors also show great performance in the WLED demonstration. The correlated color temperature (CCT) of the prototype device is 3404 K, with an extremely high Ra (97.6). Therefore, CNP:xEu2+ could be regarded as a promising alternative to blue green phosphors in nUV chip-based WLED applications.

Ester-functionalized thermally activated delayed fluorescence materials

A family of thermally activated delayed fluorescence (TADF) materials functionalized with carboxylate esters is presented herein. Owing to their suppressed concentration-quenching effect in neat films, these ester-functionalized TADF emitters could...

Synthesis and Near Infrared Luminescence Properties of a Series of Lanthanide Complexes with POSS Modified Ligands

A polyhedral oligomeric silsesquioxanes (POSS) modified 8-hydroxyquinoline derivative (denoted as Q-POSS) was synthesized and used as a ligand to coordinate with lanthanide ions to obtain a series of lanthanide complexes Ln(Q-POSS)3 (Ln = Er3+, Yb3+, Nd3+). The as-prepared lanthanide complexes have been characterized by FT-IR, UV–Vis, and elemental analysis. All these complexes showed the characteristic near-infrared (NIR) luminescence originated from the corresponding lanthanide ions under excitation. Compared with the unmodified counterparts LnQ3 (HQ = 8-hydroxyquinoline), the Ln(Q-POSS)3 complexes showed obviously increased emission intensity, which was ascribed mainly to the steric-hindrance effects of the POSS moiety in the ligands. It is believed that the POSS group could suppress undesired excimer formation and intermolecular aggregation, thus decreasing the concentration quenching effect of the corresponding lanthanide complexes.

A LUMINESCENCE PROPERTIES OF Tb, Sm CO-DOPED IN ALKALI ALUMINOBORATE GLASSES

Spectroscopic properties of Tb3+ and Sm3+ ions co-doped in alkali aluminoborate glasses (70-x-y)B2O3.28Li2O.2Al2O3.xSm2O3.yTb2O3 (ABL:Tb,Sm) fabricated by melting method have been studied. The emission intensity of Tb3+ or Sm3+ in ABL:Tb or ABL:Sm glasses is influenced by the Tb3+ or Sm3+ doping content, and the optimum concentrations of Tb3+ and Sm3+ are 0.75 mol% and 1.0 mol%, respectively. The concentration quenching effect of Tb3+ or Sm3+ in ABL:Tb,Sm glasses occurs, and the concentration quenching mechanism is f-f interaction for either Tb3+/Sm3+. The ABL:Tb,Sm glasses can produce color emission from green to red by properly tuning the relative ratio between Tb3+ and Sm3+, the emission intensity of Tb3+/Sm3+ in ABL:Tb,Sm glasses can be enhanced by the energy transfer from Tb3+/Tb3+ and Sm3+/Sm3+. The results indicate that ABL:Tb,Sm may be a promising double emission for white light emitting diodes.

Luminescent Properties of ZnxCa1–xTiO3:yPr3+ Long-Lasting Phosphors

The red long-lasting phosphors (LLPs) ZnxCa1–xTiO3:yPr3+ (ZCTP) were successfully prepared via the sol–gel method. The effects of Zn2+ content and Pr3+ molar concentration on the luminescent properties of ZCTP LLPs were characterized by X-ray diffraction, excitation and emission spectra, long-lasting decay curves and thermoluminescence (TL) curves. In this study, the results indicated that luminescent properties of Zn0.2Ca0.8TiO3:0.2 %Pr3+ phosphor was the best. In addition, when Pr3+ molar concentration reached 0.8 mol %, concentration quenching effect was obvious.

Self-host thermally activated delayed fluorescent dendrimers with flexible chains: an effective strategy for non-doped electroluminescent devices based on solution processing

Due to the encapsulation of the emissive core, the concentration quenching effect of the TADF material can be effectively restrained.