Luminescence Properties of Redispersible Tb3+-Doped GdPO4 Nanoparticles Prepared by an Ethylene Glycol Route

Quantum Cutting in KGd(CO3)2:Tb3+ Green Phosphor

Phosphors with a longer excitation wavelength exhibit higher energy conversion efficiency. Herein, quantum cutting KGd(CO₃)₂:Tb³⁺ phosphors excited by middle-wave ultraviolet were synthesized via a hydrothermal method. All the KGd(CO₃)₂:xTb³⁺ phosphors remain in monoclinic structures in a large Tb³⁺ doping range. In the KGd(CO₃)₂ host, ⁶D_3/2 and ⁶I_17/2 of Gd³⁺ were employed for quantum cutting in sensitizing levels. The excited state electrons could easily transfer from Gd³⁺ to Tb³⁺ with high efficiency. There are three efficient excited bands for quantum cutting. The excited wavelengths of 244, 273, and 283 nm correspond to the transition processes of ⁸S_7/2→⁶D_3/2 (Gd³⁺), ⁸S_7/2→⁶I_17/2 (Gd³⁺), and ⁷F₆→⁵F₄ (Tb³⁺), and the maximum quantum yields of KGd(CO₃)₂:Tb³⁺ can reach 163.5, 119, and 143%, respectively. The continuous and efficient excitation band of 273-283 nm can well match the commercial 275 nm LED chip to expand the usage of solid-state light sources. Meanwhile, the phosphor also shows good excitation efficiency at 365 nm in a high Tb³⁺ doping concentration. Therefore, KGd(CO₃)₂:Tb³⁺ is an efficient green-emitting phosphor for ultraviolet-excited solid-state light sources.

Brilliant Nonlinear Optical Response of Ho3+ and Yb3+ Activated YVO4 Nanophosphor and Its Conjugation with Fe3O4 for Smart Anticounterfeit and Hyperthermia Applications

YVO4:Ho3+/Yb3+ nanophosphors prepared by an effective polyol-mediated route show dual-mode behavior in photoluminescence. Upon 980 nm excitation, the upconversion red emission spectrum exhibits a bright red peak at ∼650 nm, characteristic of the electronic transition of the Ho3+ ion via involvement of two-photon absorption, which has been confirmed by the power-dependent luminescence study. Moreover, at 300 nm excitation, downconversion emission peaks are observed at 550, 650, and ∼755 nm. The nonradiative resonant energy transfer occurs from the V-O charge transfer band to Ho3+ ions, resulting in an improved emission of Ho3+ ions. Moreover, polyethylene glycol-coated nanoparticles make it suitable for water dispersibility; and these particles are conjugated with Fe3O4 nanoparticles to form magnetic-luminescent hybrid nanoparticles. Highly water-dispersible magnetic-luminescent hybrid material attained the hyperthermia temperature (∼42 °C) under an applied AC magnetic field. The specific absorption rate value is found to be high (138 W/g), which is more than that of pure superparamagnetic Fe3O4 nanoparticles. At 300 nm excitation, the high quantum yield value of ∼27% is obtained from YVO4:Ho3+/Yb3+, which suggests that it is a good phosphor material. By employing the neutron activation analysis technique, it is shown that nanophosphor particles can absorb Au3+ up to the ppm level. Interestingly, such nanophosphor also shows the potentiality for anticounterfeiting applications.

One-step synthesis of strongly confined, defect-free and hydroxy-terminated ZnO quantum dots

This paper reports the production of strongly confined ligand-free, defect-free, hydroxy-terminated ZnO quantum dots with a mean diameter of 1.9 nm, by radio frequency atmospheric pressure microplasma. Systematic characterization is performed to understand the surface chemistry of ZnO quantum dots. Photoluminescence studies show strong confinement effect on emission with only ultraviolet (UV) emission without any defect-related visible emission. Emission is again tested after eighteen months and confirms the QDs long-term emission stability. The mechanism responsible for this UV emission is also discussed and originates from OH-related surface terminations.

Silica-modified luminescent LaPO4 :Eu@LaPO4 @SiO2 core/shell nanorods: Synthesis, structural and luminescent properties

Monoclinic-type tetragonal LaPO₄ :Eu (core) and LaPO₄ :Eu@LaPO₄ (core/shell) nanorods (NRs) were successfully prepared using a urea-based co-precipitation process under ambient conditions. An amorphous silica layer was coated around the luminescent core/shell NRs via the sol-gel process to improve their solubility and colloidal stability in aqueous and non-aqueous media. The prepared nano-products were systematically characterized by X-ray diffraction pattern, transmission electron microscopy, energy dispersive X-ray analysis, and FTIR, UV/Vis, and photoluminescence spectroscopy to examine their phase purity, crystal phase, surface chemistry, solubility and luminescence characteristics. The length and diameter of the nano-products were in the range 80-120 nm and 10-15 nm, respectively. High solubility of the silica-modified core/shell/Si NRs was found for the aqueous medium. The luminescent core NRs exhibited characteristic excitation and emission transitions in the visible region that were greatly affected by surface growth of insulating LaPO₄ and silica layers due to the multiphonon relaxation rate. Our luminescence spectral results clearly show a distinct difference in intensities for core, core/shell, and core/shell/Si NRs. Highly luminescent NRs with good solubility could be useful candidates for a variety of photonic-based biomedical applications.

Tb3+- and Yb3+-doped novel KBaLu(MoO4)3 crystals with disordered chained structure showing down- and up-conversion luminescence

Tb³⁺/Yb³⁺ co-doped KBaLu(MoO₄)₃ with a highly disordered structure consisting of chains induces high color purity of primary green luminescence.

Anneal-induced transformation of phase structure, morphology and luminescence of GdPO4:Sm3+ nanomaterials synthesized by a hydrothermal method

GdPO₄·H₂O:xSm³⁺ nanomaterials were synthesized via a facile hydrothermal method and the effects of Sm³⁺ concentrations and annealing temperature on the crystal structures, morphologies, and luminescent properties were studied.

Highly aqueous soluble CaF2:Ce/Tb nanocrystals: effect of surface functionalization on structural, optical band gap, and photoluminescence properties

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF₂:Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF₂ and silica shell, respectively, on their surface forming as CaF₂:Ce/Tb@CaF₂ (core/shell) and CaF₂:Ce/Tb@CaF₂@SiO₂ (core/shell/SiO₂) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce³⁺/Tb³⁺-co-doped CaF₂ nanocrystals show efficient energy transfer from Ce³⁺ to Tb³⁺ ion and strong green luminescence of Tb³⁺ ion at 541 nm(⁵D₄→⁷F₅). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R ² regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing. A newly designed CaF₂:Ce/Tb nanoparticles via metal complex decomposition rout shows high dispersibility in aqueous solvents with enhanced photoluminescence. The epitaxial growth of inert CaF₂ shell and further amorphous silica, respectively, enhanced their optical and luminescence properties, which is highly usable for luminescent biolabeling, and optical bioprobe etc.

Energy-transfer from Gd(III) to Tb(III) in (Gd,Yb,Tb)PO4 nanocrystals

The photoluminescence properties of (Gd,Yb,Tb)PO4 nanocrystals synthesized via a hydrothermal route at 150 °C are reported. Energy-transfer from Gd(3+) to Tb(3+) is witnessed by the detailed analyses of excited-state lifetimes, emission quantum yields, and emission and excitation spectra at room temperature, for Tb(3+) concentrations ranging from 0.5 to 5.0 mol%. Absolute-emission quantum yields up to 42% are obtained by exciting within the (6)I7/2-17/2 (Gd(3+)) manifold at 272 nm. The room temperature emission spectrum is dominated by the (5)D4 → (7)F5 (Tb(3+)) transition at 543 nm, with a long decay-time (3.95-6.25 ms) and exhibiting a rise-time component. The (5)D3 → (7)F6 (Tb(3+)) rise-time (0.078 ms) and the (6)P7/2 → (8)S7/2 (Gd(3+)) decay-time (0.103 ms) are of the same order, supporting the Gd(3+) to Tb(3+) energy-transfer process. A remarkably longer lifetime of 2.29 ms was measured at 11 K for the (6)P7/2 → (8)S7/2 (Gd(3+)) emission upon excitation at 272 nm, while the emission spectrum at 11 K is dominated by the (6)P7/2 → (8)S7/2 transition line, showing that the Gd(3+) to Tb(3+) energy-transfer process is mainly phonon-assisted with an efficiency of ~95% at room temperature. The Gd(3+) to Tb(3+) energy transfer is governed by the exchange mechanism with rates between 10(2) and 10(3) s(-1), depending on the energy mismatch conditions between the (6)I7/2 and (6)P7/2 levels of Gd(3+) and the Tb(3+ 5)I7, (5)F2,3 and (5)H5,6,7 manifolds and the radial overlap integral values.

Luminescence, energy-transfer and tunable color properties of single-component Tb3+ and/or Sm3+ doped NaGd(WO4)2 phosphors with UV excitation for use as WLEDs

Tb³⁺ and/or Sm³⁺ codoped NaGd(WO₄)₂ microcrystals were prepared and energy transfer mechanisms of WO₄²⁻ → Sm³⁺ and Tb³⁺ → Sm³⁺ were studied. The color-tunable emissions are investigated, for nUV-LED applications.

(Gd,Yb,Tb)PO4 up-conversion nanocrystals for bimodal luminescence-MR imaging

Up-conversion (Gd,Yb,Tb)PO(4) materials and their potential for bimodal imaging have received little attention in the literature. Herein, we report the first study on the up-conversion emission of (Gd,Yb,Tb)PO(4) nanocrystals synthesized via a hydrothermal method at 150 °C. These materials exhibit ultraviolet, blue and green up-conversion emissions upon excitation with a 980 nm continuous wave laser diode. The intensity of the blue-emission band at 479 nm, ascribed to the cooperative up-conversion emission of a pair of excited Yb(3+) ions, depends on the Yb(3+)/Tb(3+) concentration ratio, calcination temperature and particle size. Strong green up-conversion emission of Tb(3+) is observed at 543 nm for the (5)D(4)→(7)F(5) transition. Relaxometry measurements reveal that the nanocrystals are efficient T(2)-weighted (negative) contrast agents which, combined with visible-light emission generated by infrared excitation, affords them considerable potential for being used in bimodal, photoluminescence-magnetic resonance, imaging.