Intercalation of cytosine into Eu3+-doped hydrocalumites and the fluorescence of the Eu3+-doped hydrocalumite response to cytosine has been investigated. XRD patterns showed that the basal spacing of Eu-doped hydrocalumite obviously increased after it exposed to various content of cytosine, revealing the intercalation of cytosine into Eu3+-doped hydrocalumite. TG-DSC curves and IR spectra of the intercalated samples are different from that of the Eu-doped hydrocalumite and cytosine, indicating the interaction between the Eu3+-doped hydrocalumite and cytosine. Fluorescent spectra suggested that the fluorescent changes of Eu3+-doped hydrocalumite depended on the concentration of cytosine solution. This fluorescent change would be potential application in biological probe in view of the biocompatibility of Ca2+ ions and the fluorescence of Eu3+ ions. Moreover, the Eu3+-doped hydrocalumite would be a healthy and cheap fluorescent material applied in biology or healing drugs fields.

A series of hybrids basing on Tb-doped CaAl hydrotalcite-like layered double hydroxides (Tb-LDH) combined with tryptophan (Trp) were prepared in an ethanol/water system. The structure, composition, and fluorescence of the hybrids have been investigated in detail by various characterizations. XRD patterns revealed some new reflections attributed to the hybrids. EDS and CHN elemental analysis results indicated that the content of C and N elements markedly increased after the Ca–Al–Tb LDH reacted with 0.01, 0.05, 0.10, and 0.25 mol L−1 Trp ethanol/water solutions, respectively. IR spectra showed that bands attributed to Trp appeared as the Tb-LDH reacted with 0.10 and 0.25 mol L−1 Trp. A thermal decomposition study found that the TG–DTG curves of hybrids were different. Fluorescent spectra suggested that the green emission due to the 5D4–7F5 transition of Tb3+ was almost quenched. Based on these results, the hybridization mechanism of Tb-LDH and Trp was discussed.

An important material applied in biological fluorescent detector and medical treatment is highly desired in view of the biocompatibility and fluorescent property. Here, Tb-doped CaAl-layered double hydroxides with Ca2+/(Al3+ + Tb3+) molar ratio of 1.0, 2.0, 3.0, and 4.0 have been successfully prepared in a mixed solution of ethanol and water in a reasonable proportion. Chemical compositional analyses revealed that the experimental value of Ca2+/(Al3+ + Tb3+) molar ratio present in the samples was close to the initial value of Ca2+/(Al3+ + Tb3+) molar ratio of raw reactants. In the X-ray diffraction results, it was found that the typical layered double hydroxides structure can be kept between the Ca2+/(Al3++Tb3+) molar ratio of 1.0 and 4.0. The structural type of the Tb-doped CaAl-layered double hydroxides was monoclinic form when the Tb content was less than of 3.0 %, while rhombohedral form appeared and retained as the content of Tb3+ is kept between 3.0 and 5.28 wt%. Photoluminescence shows strong green emissions attributed to 5D4-7FJ (J = 3, 4, 5, 6) transition of Tb3+ ions incorporated in the Tb-doped CaAl-layered double hydroxides.A series of Tb-doped CaAl-LDHs with different molar ratio of Ca2+/(Al3+ + Tb3+) have been synthesized by co-precipitation in a mixed ethanol/water system. Strong green emission appeared in the Tb-doped CaAl-LDH. The Tb–CaAl-LDHs may be a promising biological fluorescent material because of the biocompatibility of Ca2+ ions as well as the fluorescent property of Tb3+ ions.Open image in new window

In view of the widely used red phosphor Y2O2S:Eu3+ suffering from expensive and low efficiency, it is urgent to develop a new cheap and high efficiency red-emitting phosphor. Therefore, a new red-emitting phosphor Ca12Al14-xEuxO32Cl2 derived from Eu3+-doped hydrocalumite by phase transition at low temperature was proposed. Various characterizations, including X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM/EDS), and photoluminescence (PL), were employed to investigate the composition, structure, and photoluminescence of samples. XRD results revealed that the Ca12Al14-xEuxO32Cl2 phase formed after the Eu3+-doped hydrocalumite was thermal treatment at 600 °C for 2 h. The crystallinity of the Ca12Al14-xEuxO32Cl2 phase gradually improved with temperature up to 800 and 1000 °C. Compositional analyses indicated the chemical formula of the Ca12Al14-xEuxO32Cl2 phase estimated to be Ca12Al12.56Eu1.44O32Cl2 and Ca12Al12.49Eu1.51O32Cl2 for the samples annealed at 600 and 1000 °C, respectively. The Ca12Al14-xEuxO32Cl2 phase can be efficiently excited by near ultraviolet light and shows strong red-orange emissions at 618 and 589 nm, due to 5D0-7F2 and 5D0-7F1 transition of Eu3+, respectively. The strongest red-orange emissions appeared in the sample annealed at 600 °C. The present Ca12Al14-xEuxO32Cl2 may be a promising candidate for cheap and high efficiency red-emitting phosphors applied in LEDs.

•Amorphous Eu3 +/Tb3 + co-doped MgAl hydroxide salts were prepared.•Tunable light emissions attributed to Tb3 + and Eu3 + appeared in the amorphous phase.•The emissions of samples depending on their phase transition have been studied.•The emissions of Eu3 + and Tb3 + doped in amorphous phase are better than that in multi-crystalline phases.Two of Eu3 +/Tb3 + co-doped amorphous Mg-Al double hydroxide salts, with Eu3 +/Tb3 + molar ratios of 1/4 and 4/1, were prepared and their photoluminescence dependence on phase transition has been investigated. Our results revealed that the co-doped amorphous samples exhibited excellent green emissions due to 5D4 → 7FJ (J = 5, 6) transitions of Tb3 + under the excitation of 350, 370 and 380 nm, and red emissions due to 5D0 → 7FJ (J = 1, 2) transitions of Eu3 + under the excitation of 395 and 468 nm. Moreover, the emission intensity is dependent on the Eu3 +/Tb3 + molar ratio. When the amorphous Eu3 +/Tb3 + co-doped samples were annealed at 200 and 300 °C, the phase transition was unobservable. After the samples were annealed at 500 °C, the samples began to transform. Further, the multi-crystalline phases formed after the samples were annealed at 700 and 900 °C. Moreover, the emissions attributed to Eu3 + and Tb3 + incorporated in the amorphous host are greatly stronger than that of in the multi-crystalline host. These results indicated the amorphous phase was more favorable for the emissions of Eu3 + and Tb3 + compared with that of the multi-crystalline phases.Two of Eu3 +/Tb3 + co-doped amorphous Mg-Al double hydroxide salts, with Eu3 +/Tb3 + molar ratio of 1/4 (I) and 4/1(II), were prepared and their photoluminescence depending on phase transition has been investigated. Results revealed that the Eu3 +/Tb3 + co-doped amorphous samples exhibited excellent tunable emissions under different excitation wavelengths. Moreover, the emission intensity of Eu3 + and Tb3 + present in the amorphous host is greatly stronger than that of the multi-crystalline host, indicating the amorphous Mg-Al double hydroxide salts would be potential application in white-light LED.Download high-res image (183KB)Download full-size image

•A new green phosphor Ca12Al14O32Cl2: Tb3+ was prepared through phase transition.•The Ca12Al14O32Cl2: Tb3+ has characteristic cubic structure, and exhibited strong green emission.•The present Ca12Al14O32Cl2: Tb3+ derived from Tb-doped Ca-Al LDH at low temperature.A new green phosphor Ca12Al14O32Cl2: Tb3+ derived from Tb-doped Ca-Al layered double hydroxide (Tb-doped CaAl-LDH) was prepared through phase transition route. The X-ray diffraction measurement results revealed that the Tb-doped CaAl-LDH transformed into Ca12Al14O32Cl2:Tb3+ phase at 600 °C. With temperature varying from 600, 800–1000 °C, the crystallinity of the Ca12Al14O32Cl2:Tb3+ phase gradually improved. Compositional analyses suggested the chemical formula of the Ca12Al14O32Cl2:Tb3+ phase estimated to be Ca12Al13.52Tb0.48O32Cl2. The Ca12Al13.52Tb0.48O32Cl2 phase can be efficiently excited by near ultraviolet light and show strong green emissions attributed to 5D4→7FJ (J = 5, 6) transition of Tb3+. The present Ca12Al13.52Tb0.48O32Cl2 may be a promising candidate for green phosphor applied in LED.

•New binary Mg/Tb Mg/Tb-LDH was synthesized.•They are hexagonal structure.•The Mg/Tb-LDH exhibits excellent photoluminescence.A series of binary Mg/Tb layered double hydroxides (Mg/Tb-LDH) with different Mg2 +/Tb3 + molar ratios of 2.0, 3.0, 4.0, and 5.0 have been synthesized in ammonia water media by hydrothermal method. Various characterizations, including inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray diffraction (XRD), and photoluminescent spectra (PL), etc., were used to study the composition, structure, and photoluminescent property of samples. Results revealed that the molar ratios of Mg2 +/Tb3 + present in the samples approximated to that of the initial molar ratios of chemical reagents. All the Mg/Tb-LDH samples have similar hexagonal structure as that of the brucite Mg(OH)2 despite their lattice c values are greatly larger than that of the Mg(OH)2. These Mg/Tb-LDH exhibited good photoluminescence. Moreover, the emissions due to 5D4 → 7FJ (J = 5, 6) transitions of Tb3 + gradually enhanced as the Mg2 +/Tb3 + molar ratios varied from 5.0, 4.0 to 3.0; then markedly decreased with the Mg2 +/Tb3 + molar ratio down to 2.0. The strongest emissions were observable to be at Mg2 +/Tb3 + molar ratio of 3.0. This new binary Mg/Tb-LDH may be potential application as luminescent materials.A series of binary Mg/Tb layered double hydroxides (Mg/Tb-LDHs) with different Mg2 +/Tb3 + molar ratios have been synthesized in ammonia water media by hydrothermal method. The composition, structure, and photoluminescent property of samples have been studies. All the Mg/Tb-LDHs samples have similar structure, and exhibited good photoluminescence. Moreover, the strongest emissions were observable to be at Mg2 +/Tb3 + molar ratio of 3.0. This new binary Mg/Tb-LDH would be potential application as luminescent materials.Download high-res image (172KB)Download full-size image

AbstractThis paper presented the photoluminescence of Tb-doped Mg-Al layered double hydroxides (Tb-doped MgAl-LDHs) depending on phase transition caused by annealing. Tb-doped MgAl-LDHs structure transformed from hexagonal LDHs, cubic MgO to spinel MgAl2O4 phase as temperature varied from 200 to 1000 °C. Emission and excitation spectra of Tb-doped MgAl-LDHs obviously changed with phase transformation. The emissions of Tb3+ ions attributed to 5D4→7FJ transitions (J=3, 4, 5, 6) were observed in the emission spectra of all the Tb-doped samples. The ratio of (5D4→7F5)/(5D4→7F6) emission intensity, which was sensitive to surroundings of Tb3+ ion, markedly enhanced with temperature rising to 600 from 400 °C. Over 600 °C, the ratio of (5D4→7F5)/(5D4→7F6) intensity tended to decreasing up to 1000 °C. The change concerning the ratio of the (5D4→7F5)/(5D4→7F6) emission intensity might be due to various surroundings of Tb3+ induced by phase transformation.The photoluminescence and transition of Tb-doped MgAl-LDHs depending on thermal treatment indicated that the emission due to 5D4→7FJ (J=5,.6) transition of the Tb3+ ions changed markedly with increasing temperatures. The changed emission should result from phase transformation caused by thermal treatment

A series of hybrids based on Tb-doped Zn-Al layered double hydroxides (Tb-LDHs) combined with tryptophan (hereafter shortened as Try) were synthesized by soft-chemical method. The composition, structure, and fluorescence of the Tb-LDH/Try hybrids were analyzed by various characterizations. Compositional analysis indicated that the content of tryptophan present in the hybrids gradually increased while the Tb-LDH reacted with 0.05, 0.1, and 0.25 mol/L Try solution, respectively. XRD results revealed that new reflections appeared in the Tb-LDH/Try hybrids. TGA curves of the Tb-LDH/Try hybrids were different from that of Tb-LDH and Try. IR spectra manifested that the IR spectra of the hybrids were characteristic of the Try and Tb-LDH. Fluorescent spectra suggested that the green emission due to 5D4→7F5 transition of Tb3+ greatly decreased but not quenched, and the emission attributed to Try obviously increased. Meanwhile the fluorescent spectra of Tb-LDH/Try hybrids presented broad continuous bands in visible region.Fluorescent property of hybrids based on Tb-doped ZnAl-LDH and tryptophan

The paper describes a study on the green emission of a Tb-doped Mg-Al layered double hydroxide (Tb-LDH) response to L-lysine (Lys). Fluorescent study was found that the Tb-LDH exhibited strong green emission due to 5D4-7FJ (J = 5, 6) transition of Tb3+, and the green emission almost quenched while the Tb-LDH was exposed to 0.01, 0.05, 0.1, 0.25, and 0.5 mol·L−1 Lys solution, respectively. Meanwhile the emission attributed to Lys markedly increased as the Tb-LDH was exposed to 0.01 and 0.05 mol·L−1 Lys solution, then decreased as the concentration of Lys solution further increased to 0.5 from 0.05 mol·L−1. The green emission of Tb-LDH optimal response to Lys happened at 0.05 mol·L−1 of Lys solution. XRD results revealed that no reflections ascribed to Lys appeared in the composites of Tb-LDH and Lys. IR spectra suggested that the IR spectra of Tb-LDH obviously changed after it was exposed to Lys solution. These results indicated that the green emission of Tb-LDH response to Lys was possibly owing to interaction between the Tb-LDH and Lys. Moreover, this interaction between the Tb-LDH and Lys may be resulted from absorption. The green emission of Tb-LDH response to Lys would be potential application in detecting L-lysine.

•Composites based on ternary Zn1−xCdxO dispersed in octosilicate were synthesized.•The optical property of Zn1−xCdxO can be modified by disordered stacking of octosilicate.•The sizes of ternary Zn1−xCdxO dispersed in octosilicate are about 5–10 nm.Composites based on ternary Zn1−xCdxO nanoparticles dispersed in octosilicate were obtained by ion exchange followed by thermal treatment. Compositional analyses revealed the host octosilicate containing ternary Zn1−xCdxO nanoparticles. X-ray diffraction (XRD) patterns show no reflections in the XRD patterns of all the composites, indicating a disordered structure of the composite. Ultraviolet–visible (UV–vis) diffuse reflection spectra suggested that the band edges of the composites shifted to low energy with increasing amount of Cd present in the composites. The photoluminescent (PL) spectra showed that only a strong peak at 412 nm appeared in all the composites, which was very different from that of the similar compositional Zn1−xCdxO without octosilicate. Transmission electron microscopy (TEM) observation confirmed that the ordered stack of layered octosilicate became disordered, and the sizes of Zn1−xCdxO nanoparticles dispersed in disordered silicate were about 5–10 nm. These results revealed that the optical property of Zn1−xCdxO can be modified by disordered octosilicate.Composites based on ternary Zn1−xCdxO nanoparticles dispersed in octosilicate were obtained by ion exchange and following thermal treatment. It was found that the optical property of Zn1−xCdxO changed obviously after it was introduced to host layered silicate. TEM confirmed that the sizes of Zn1−xCdxO dispersed in host silicate are estimated to be 5–10 nm.

A new composite based on polymolybdate incorporated in layered magadiite has been synthesized via a exfoliation/self-assembly process. Various techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), Raman spectroscopy, thermogravimetric (TG) analysis, UV–vis spectroscopy, and transmission electron microscopy (TEM), have been employed to characterize the composite. Results indicated that the polymolybdate particles were incorporated into the layered magadiite. Upon the irradiation of visible light (420–630 nm), the composite changed color from yellow to dark blue; moreover, the color can be bleached upon exposure to a 15% H2O2 solution. The visible-light illumination and H2O2 treatment can be repeated in excess of 10 times. The mechanism of photochromism has been investigated, and the reversibility is attributed to the hydration property of host magadiite and oxidative ability of H2O2 solution.

An Eu-doped ZnAl-layered double hydroxide (ZnAl-LDH) was synthesized by the coprecipitation method at room temperature. A set of as-prepared samples were subjected to annealing at various temperatures from 100, 200, 300, 500, 600, 700, to 800 °C for 1 h, respectively. The annealed samples were characterized by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscope (SEM), and photoluminescence (PL). New phases occurred with annealing temperatures above 300 °C. Meanwhile, the emissions of Eu3+ ions described by 5D0–7FJ transition (J=1, 2, 3, 4), especially for the 5D0–7FJ transition (J=1, 2), varied with phase transitions of its local host materials from ZnAl-LDH, ZnO, to mixed phases of ZnO and ZnAl2O4. The emissions of Eu3+ ions depending on its host materials were discussed.Research highlights► The emissions of Eu3+ ions incorporated into layers of LDHs dependence on host phase transitions resulted from annealing temperature were investigated for the first time. ► Strong emissions attributed to 5D0–7FJ (J=1, 2, 3, 4) of Eu3+ located in ZnAl–Cl LDH were observed. ► The emissions of Eu3+ ions in ZnAl–Cl LDH were higher than those in ZnO phase and mixed phases of ZnO and ZnAl2O4, indicating that the structure of the ZnAl–Cl LDH more favored the emissions of Eu3+ ions.

A series of Mg–Al–Eu ternary hydrotalcite-like layered double hydroxides (LDHs), with Eu/Al atomic ratios of ∼0.06 and Mg/(Al+Eu) atomic ratios ranging from 1.3 to 4.0, were synthesized by a coprecipitation method. The Mg–Al–Eu ternary LDHs were investigated by various techniques. X-ray diffraction (XRD) results indicated that the crystallinity of the ternary LDHs was gradually improved with the increase of Mg2+/(Al3++Eu3+) molar ratio from 1.3/1 to 4/1, and all the samples were a single phase corresponding to LDH. The photoluminescent (PL) spectra of the ternary Mg–Al–Eu LDHs were described by the well-known 5D0–7FJ transition (J=1, 2, 3, 4) of Eu3+ ions with the strongest emission for J=2, suggesting that the host LDH was favorable to the emissions of Eu3+ ions. The asymmetry parameter (R) relevant to 5D0–7FJ transition (J=1, 2) dependant of the atomic ratios of Mg2+/(Al3++Eu3+) was discussed, and was consistent with the result of XRD.A series of Mg–Al–Eu ternary hydrotalcite-like layered double hydroxides (LDHs), with Mg/(Al+Eu) atomic ratios ranging from 1.3/1, 2/1 3/1 to 4/1, were synthesized by a coprecipitation method. The photoluminescent spectra of the Mg–Al–Eu ternary LDHs are described by the well-known 5D0–7FJ transition (J=1, 2, 3, 4) of Eu3+ ions with the strongest emission for J=2.

CdS/niobate composite synthesized by exfoliation/self-assembly processing was first reported. The processing presents two steps, namely (i) restacking of [Ca2Nb3O10]nn− nanosheets in Cd(NH3)42+ solution and (ii) forming of CdS/niobate composite by adding Na2S to the (i) reacting system. The as-prepared composite of CdS/niobate can be indexed to tetrahedral symmetry (lattice parameters, a 5.462(5) Å; c 17.3303(1) Å) on basis of X-Ray powder diffraction result. The scanning electron microscope and energy dispersive spectrometer observation demonstrates the uniform distributions of Ca, Nb, O, Cd, and S elements in the particles. The UV–vis absorption edge of the CdS/niobate composite (CdS coated with host niobate) shows blue shift (shifts to high energy) compared with that of the uncoated CdS particles.

ZnO/niobate composites were first synthesised through the exfoliation of layered niobate and restacking of nanosheets in Zn(NH3)42+ solution, followed by heat-treatment. The effects of pH and content of Zn(NH3)42+ solution on the structure and interlayer guests of the self-assembled compounds were systematically investigated. All the as-prepared samples obtained at the conditions of 0.1 mol L−1Zn(NH3)42+ with pH from 11.2 to 12.7, can be indexed to tetragonal symmetry. The amount of interlayer Zn-species tends to decrease slightly as the pH value increases, while it increases markedly with an increase of Zn(NH3)42+ content and subsequently affects the photoluminescence of the heated-samples. Photoluminescent spectra of all the heated-samples show blue-shifts of 0.15–0.22 eV with respects to the bulk ZnO band gap (3.26 eV) due to quantum confinement. The UV emission at 359 nm obviously weakens and the emission at 398 nm gradually enhances as content of Zn(NH3)42+ increases from 0.1 to 0.8 mol L−1.

Eu-doped ZnAl-layered double hydroxides (ZnAl–LDHs) with various Zn2+/(Al3++Eu3+) molar ratios from 1:1, 2:1, 3:1, to 4:1 were first synthesized by the coprecipitation method at room temperature and the Eu3+/Al3+ molar ratio of 0.06 was almost maintained. The obtained solids were characterized by powder X-ray diffraction (XRD), photoluminescent spectrum (PL), scanning electron microscope (SEM), infrared spectroscopy (IR), and thermogravimetric (TG) analysis. XRD results show that the crystallinity of the Eu-doped products gradually was improved when the Zn2+/(Al3++Eu3+) molar ratio was higher than 2. The photoluminescent spectra of the Eu-doped ZnAl–LDHs are described by the well-known 5D0–7FJ transition (J = 1, 2, 3, 4) of Eu3+ ions with the strongest emission for J = 2.

A novel synthesis of CdS1−xSex solid solution is presented, which is based on the room temperature reaction among CdO(CdCO3, CdCl2), Na2S·9H2O and Se powders. XRD and composition analysis results show that the composition of CdS1−xSex is related to the Cd sources. Namely, CdS0.54Se0.46 has been obtained from CdO precursor, and CdS0.75Se0.25 has been obtained from CdCO3 or CdCl2 precursors. The excess Na2S·9H2O plays crucial role for the formation of CdS1−xSex, by which the solid phase reaction mechanism has been discussed. The optical properties of CdS0.54Se0.46 and CdS0.75Se0.25 were characterized by absorption spectrum and fluorescent spectrum, respectively. The average sizes of particles are about 1.67–2.49 μm by the Ls601-Laser particle analysis instrument measurement.