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NaYF4 is a superior host matrix to study the luminescence properties of lanthanide (Ln3+) ions. Ln3+ ions in hexagonal-phase NaYF4 (β-phase) nanocrystals (NCs) exhibit strong luminescence via an upconversion process compared to cubic NaYF4 (α-phase) NCs. However, in Ce3+/Ln3+-doped NaYF4 NCs (Ln=Tm, Tb, Sm, Dy) the α-phase NaYF4 NCs shows strong luminescence compared to their counterpart β-phase NCs despite the latter being much larger in size. This is attributed to comparatively large overlap between Ce3+ ions emission band with excited energy levels of those Ln3+ ions in α-phase compared to β-phase NCs. This difference is attributed to different crystal-field splitting of Ce3+ ions 4f-5d band in different crystal environments of the α-phase (cubic crystal field environment) and β-phase (trigonal prismatic with equatorials crystal field environment) NaYF4 NCs with respect to their barycenter. The enhanced luminescence from α-phase NaYF4 NCs is advantageous as they are prepared at a relatively lower temperature and shorter reaction times compared to β-NaYF4 NCs. [ABSTRACT FROM AUTHOR]

We report the enhancement of both visible and near infrared (NIR) emissions from Nd3+ ions via Ce3+ sensitization in colloidal nanocrystals for the first time. This is achieved in citrate capped Nd3+-doped CeF3 nanocrystals under ultraviolet (UV) irradiation (λex = 282 nm). The lasing transition (4F3/2→4I11/2) at 1064 nm from Nd3+-doped CeF3 nanocrystals has much higher emission intensity via Ce3+ ion sensitization compared to the direct excitation of Nd3+ ions. The nanocrystals were prepared using a simple microwave irradiation route. Moreover, the study has been extended to Sm3+-doped CeF3 nanocrystals which show strong characteristic emissions of Sm3+ ions via energy transfer from Ce3+ ions. The energy transfer mechanism from Ce3+ to Nd3+ and Sm3+ ions is proposed. [ABSTRACT FROM AUTHOR]

We report on the synthesis of diamond shaped Ln3+-doped LiYbF4 (Ln = Tm and Er) nanocrystals with flat edges via the thermal decomposition method. Strong near-infrared emissions at 0.8 μm, 1.47 μm and 1.53 μm are observed from colloidal dispersions of Tm3+-doped and Er3+-doped LiYbF4 nanocrystals, respectively, under 0.98 μm diode laser excitation. The NIR emission intensities for Tm3+-doped and Er3+-doped LiYbF4 nanocrystals are comparable with those of the sodium counterpart NaYbF4, suggesting that LiYbF4 is also an excellent host matrix for lanthanide ions to obtain strong NIR emissions in colloidal solutions of LiYbF4 (Tm3+ or Er3+) nanocrystals. [ABSTRACT FROM AUTHOR]

This article describes a green synthetic approach to prepare water dispersible perovskite-type Eu3+-doped KZnF3 nanoparticles, carried out using environmentally friendly microwave irradiation at low temperature (85 °C) with water as a solvent. Incorporation of Eu3+ ions into the KZnF3 matrix is confirmed by strong red emission upon ultraviolet (UV) excitation of the nanoparticles. The nanoparticles are coated with poly(acrylic acid) (PAA), which enhances the dispersibility of the nanoparticles in hydrophilic solvents. The strong red emission from Eu3+ ions is selectively quenched upon addition of CuII ions, thus making the nanoparticles a potential CuII sensing material. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA), with recovery of almost 90 % of the luminescence. If the nanoparticles are strongly attached to a positively charged surface, dipping the surface in a CuII solution leads to the quenching of Eu3+ luminescence, which can be recovered after dipping in an EDTA solution. This process can be repeated for more than five cycles with only a slight decrease in the sensing ability. In addition to sensing, the strong luminescence from Eu3+-doped KZnF3 nanoparticles could be used as a tool for bioimaging. [ABSTRACT FROM AUTHOR]

We report a facile microwave-assistedgreen synthetic route forcolloidal poly(vinyl alcohol) (PVA)-coated europium (Eu3+)-doped luminescent heavy metal bismuth oxyhalide (BiOX; X = Cl,Br, I) nanoflakes at low temperature and examine their structural,optical, and photocatalytic characteristics. PVA coating onto thesurface of the nanoflakes endows them with hydrophilic nature. BothEu3+-doped BiOCl and BiOBr nanoflakes exhibit strong opticalproperties related to Eu3+and Bi3+which arequenched in case of Eu3+-doped BiOI matrix. These resultsare supported by Eu3+photoluminescence lifetime valuesof 0.61 ms, 0.59 ms, and 8.9 μs, respectively. The former twomatrices have quite similar crystal field environments as deducedfrom the asymmetric ratios of 5D0→ 7F2(614 nm) and 5D0→ 7F1(591 nm) transitions. In addition to possessinginteresting photoluminescence properties, a comparison of the photocatalyticactivity of Eu3+-doped BiOX (X = Cl, Br, I) nanoflakes,with corresponding estimated band gaps of 3.36, 2.74, and 1.67 eVhas been evaluated using Rhodamine B (RhB) dye under visible lightirradiation. The nanoflakes exhibited 100% dye degradation under visiblelight irradiation. Eu3+-doped BiOCl nanoflakes manifestedhigher photocatalytic efficiency compared to the other matrices followingapparent first-order kinetics. Such a boost in efficiency is attributedto their high surface area to volume ratios, layered crystalline structures,indirect band gap nature, and ability to utilize broad bands in thesolar spectrum. [ABSTRACT FROM AUTHOR]

Heavy metal fluorides like BiF3 as a host for lanthanide ions are of interest as bismuth is the only heavy metal that is nontoxic. In this work, we report the synthesis of highly water-dispersible ultrasmall BiF3 nanoparticles about 6 nm in size within a poly(vinyl pyrrolidone) matrix by a hydrothermal method. Microscopy analysis reveals that the nanoparticles are well separated and confined within the polymer network. These nanoparticles were found to be excellent hosts for lanthanide (Ln3+) ions. Through suitable Ln3+ doping, BiF3 exhibits strong emissions in the visible region upon both UV and near infrared (NIR) excitations. The non-toxicity of both bismuth and PVP can be advantageous for the potential use of BiF3 nanoparticles in drug delivery and bioimaging. [ABSTRACT FROM AUTHOR]

The colloidal growth of ZnO exhibits interesting dynamics, which is generally probed using absorbance measurements. Here, we have shown that the sharp luminescent signals from the Eu3+ ions act as a potential luminescent spectral probe to follow the growth of ZnO nanostructures. The Eu3+-doped ZnO nanocrystals were synthesized by a colloidal method. The asymmetry ratio calculated from the Eu3+ emission intensity peaks (5D0→7F2/5D0→7F1) gradually decrease with the increase in the size of the ZnO nanostructures. This is attributed to the increase in the surface related defects as the size of the ZnO nanocrystals is increased. The above result is supported by controlling the growth of the ZnO nanocrystals with capping ligands. The Eu3+ luminescence intensity hardly is affected upon ligand capping. Additional experiments such as lifetime measurements and photocatalytic activity of ZnO strongly indicate that Eu3+ can be used as a potential tool to follow the growth of colloidal ZnO nanostructures. We believe the study can be extended to understand the growth mechanism of several other colloidal nanostructures. [ABSTRACT FROM AUTHOR]

A series of Eu3+-doped pyridine functionalized YF3 microcrystals were synthesized at low temperature (70 °C) using a simple colloidal route. The shape and phase of the YF3 microcrystals were tuned using different fluoride sources (e.g. NaF, NaBF4 and NH4F). Cubic phase of the microcrystals with flower like morphology was achieved with NaF as fluoride source, while use of NaBF4 and NH4F led to the formation of orthorhombic phase with bundle and rice flake like morphology, respectively. This difference in the morphology and phase is reflected in their optical properties as well. A mechanism has been proposed for the formation of different morphology of YF3 microcrystals. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrum (FTIR), photoluminescence (PL) and lifetime measurements were used to characterize the structural and optical properties of microcrystals. [ABSTRACT FROM AUTHOR]

NaYF 4 is a superior host matrix to study the luminescence properties of lanthanide (Ln 3+ ) ions. Ln 3+ ions in hexagonal-phase NaYF 4 (β-phase) nanocrystals (NCs) exhibit strong luminescence via an upconversion process compared to cubic NaYF 4 (α-phase) NCs. However, in Ce 3+ /Ln 3+ -doped NaYF 4 NCs (Ln=Tm, Tb, Sm, Dy) the α-phase NaYF 4 NCs shows strong luminescence compared to their counterpart β-phase NCs despite the latter being much larger in size. This is attributed to comparatively large overlap between Ce 3+ ions emission band with excited energy levels of those Ln 3+ ions in α-phase compared to β-phase NCs. This difference is attributed to different crystal-field splitting of Ce 3+ ions 4f-5d band in different crystal environments of the α-phase (cubic crystal field environment) and β-phase (trigonal prismatic with equatorials crystal field environment) NaYF 4 NCs with respect to their barycenter. The enhanced luminescence from α-phase NaYF 4 NCs is advantageous as they are prepared at a relatively lower temperature and shorter reaction times compared to β-NaYF 4 NCs., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the enhancement of both visible and near infrared (NIR) emissions from Nd(3+) ions via Ce(3+) sensitization in colloidal nanocrystals for the first time. This is achieved in citrate capped Nd(3+)-doped CeF3 nanocrystals under ultraviolet (UV) irradiation (λex = 282 nm). The lasing transition ((4)F3/2 → (4)I11/2) at 1064 nm from Nd(3+)-doped CeF3 nanocrystals has much higher emission intensity via Ce(3+) ion sensitization compared to the direct excitation of Nd(3+) ions. The nanocrystals were prepared using a simple microwave irradiation route. Moreover, the study has been extended to Sm(3+)-doped CeF3 nanocrystals which show strong characteristic emissions of Sm(3+) ions via energy transfer from Ce(3+) ions. The energy transfer mechanism from Ce(3+) to Nd(3+) and Sm(3+) ions is proposed.

We report a green synthetic approach to the synthesis of water dispersible Ce(3+)/Tb(3+)-doped SrF2 nanocrystals, carried out using environment friendly microwave irradiation with water as solvent. The nanocrystals display strong green emission due to energy transfer from Ce(3+) to Tb(3+) ions. This strong green emission from Tb(3+) ions is selectively quenched upon addition of Cu(2+) ions, thus making the nanocrystals a potential Cu(2+) ions sensing material. There is barely any interference by other metal ions on the detection of Cu(2+) ions and the detection limit is as low as 2 nM. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA) with the recovery of almost 90% of the original luminescence. The luminescence quenching and recovery cycle was repeated multiple times without much effect on the sensitivity. The study was extended to real world water samples and obtained similar results. In addition to the sensing, we strongly predict the small size and high luminescence of the Ce(3+)/Tb(3+)-doped SrF2 nanocrystals can be used for bioimaging applications.

An intense single-band blue emission at λ=450 nm is observed from Tm(3+) ions through Ce(3+) sensitization, for the first time, in colloidal Ce(3+) /Tm(3+) -doped NaYF4 nanocrystals. The intense Tm(3+) emission through broad-band excitation is advantageous for developing luminescent nanocomposites because they can be easily incorporated into polymers. The composites can easily be coated over UV light-emitting diodes (LEDs) to develop phosphor-based blue LEDs., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This article describes a green synthetic approach to prepare water dispersible perovskite-type Eu3+-doped KZnF3 nanoparticles, carried out using environmentally friendly microwave irradiation at low temperature (85 8C) with water as a solvent. Incorporation of Eu3+ ions into the KZnF3 matrix is confirmed by strong red emission upon ultraviolet (UV) excitation of the nanoparticles. The nanoparticles are coated with poly(acrylic acid) (PAA), which enhances the dispersibility of the nanoparticles in hydrophilic solvents. The strong red emission from Eu3+ ions is selectively quenched upon addition of CuII ions, thus making the nanoparticles a potential CuII sensing material. This sensing ability is highly reversible by the addition of ethylenediaminetetraacetic acid (EDTA), with recovery of almost 90% of the luminescence. If the nanoparticles are strongly attached to a positively charged surface, dipping the surface in a CuII solution leads to the quenching of Eu3+ luminescence, which can be recovered after dipping in an EDTA solution. This process can be repeated for more than five cycles with only a slight decrease in the sensing ability. In addition to sensing, the strong luminescence from Eu3+-doped KZnF3 nanoparticles could be used as a tool for bioimaging.

Heavy metal fluorides like BiF3 as a host for lanthanide ions are of interest as bismuth is the only heavy metal that is nontoxic. In this work, we report the synthesis of highly water-dispersible ultrasmall BiF3 nanoparticles about 6 nm in size within a poly(vinyl pyrrolidone) matrix by a hydrothermal method. Microscopy analysis reveals that the nanoparticles are well separated and confined within the polymer network. These nanoparticles were found to be excellent hosts for lanthanide (Ln(3+)) ions. Through suitable Ln(3+) doping, BiF3 exhibits strong emissions in the visible region upon both UV and near infrared (NIR) excitations. The non-toxicity of both bismuth and PVP can be advantageous for the potential use of BiF3 nanoparticles in drug delivery and bioimaging., (Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Monodispersed Yb(3+)(20%)/Er(3+)(2%)-doped BaLnF(5) (Ln = La, Gd, Lu) nanocrystals were synthesized by a thermal decomposition method. The study reveals that the size of the nanocrystals scales down with the Ln(3+) size without affecting the phase and shape of the nanocrystals. This is supported by the microscopic and optical properties.