Yufeng Chen

Photoluminescence of Tb-doped MgAl-LDHs depending on phase transition caused by annealing

Abstract This 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 MgAl 2 O 4 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 Tb 3+ ions attributed to 5 D 4 → 7 F J transitions ( J =3, 4, 5, 6) were observed in the emission spectra of all the Tb-doped samples. The ratio of ( 5 D 4 → 7 F 5 )/( 5 D 4 → 7 F 6 ) emission intensity, which was sensitive to surroundings of Tb 3+ ion, markedly enhanced with temperature rising to 600 from 400 °C. Over 600 °C, the ratio of ( 5 D 4 → 7 F 5 )/( 5 D 4 → 7 F 6 ) intensity tended to decreasing up to 1000 °C. The change concerning the ratio of the ( 5 D 4 → 7 F 5 )/( 5 D 4 → 7 F 6 ) emission intensity might be due to various surroundings of Tb 3+ induced by phase transformation.

Study on structure and fluorescence of Tb-doped CaAl LDHs prepared in ethanol/water system

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+u2009+u2009Tb3+) 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+u2009+u2009Tb3+) molar ratio present in the samples was close to the initial value of Ca2+/(Al3+u2009+u2009Tb3+) 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 3.0u2009%, while rhombohedral form appeared and retained as the content of Tb3+ is kept between 3.0 and 5.28u2009wt%. Photoluminescence shows strong green emissions attributed to 5D4-7FJ (Ju2009=u20093, 4, 5, 6) transition of Tb3+ ions incorporated in the Tb-doped CaAl-layered double hydroxides.Graphical AbstractA series of Tb-doped CaAl-LDHs with different molar ratio of Ca2+/(Al3+u2009+u2009Tb3+) 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.

Green Emission of Tb-doped Mg-Al Layered Double Hydroxide Response to L-lysine

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 (Jxa0=xa05, 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 0.5xa0mol·L−1 Lys solution, respectively. Meanwhile the emission attributed to Lys markedly increased as the Tb-LDH was exposed to 0.01 and 0.05xa0mol·L−1 Lys solution, then decreased as the concentration of Lys solution further increased to 0.5 from 0.05xa0mol·L−1. The green emission of Tb-LDH optimal response to Lys happened at 0.05xa0mol·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.

Study on a Novel Binary Zn n Eu Layered Double Hydroxide with Excellent Fluorescence

A group of binary ZnnEu-LDHs with Zn2+/Eu3+ molar ratios of 5.0, 6.0, 7.0, and 8.0 have been obtained in ammonia water media by hydrothermal treatment. The structure, composition, and fluorescent property of samples have been investigated using various techniques. Compositional analyses revealed that the composition of samples was in agreement with that of the initial reactants. X-ray diffraction (XRD) suggested that the ZnnEu-LDHs exhibited typical layered structure with orthorhombic symmetry. All the ZnnEu-LDHs appeared strong red emissions attributed to 5D0 → 7FJ (Ju2009=u20091, 2) transitions of Eu3+. Moreover, the intensity of emissions due to 5D0 → 7FJ (Ju2009=u20091, 2) transitions of Eu3+ tended to increase with the Zn2+/Eu3+ molar ratio varied from 8.0, 7.0 to 6.0, then decreased as the Zn2+/Eu3+ molar ratio reduced to 5.0. The strongest fluorescence was found to be at Zn2+/Eu3+ molar ratio of 6.0. Further the fluorescence decay spectra show that the ZnnEu-LDH have similar behavior of fluorescent decay and decayed more slowly than that of the Eu(OH)3. These results indicate that the novel binary ZnnEu-LDHs have better fluorescent property and may be potential application as fluorescent materials.

Study on hybrization of Tb3+-doped CaAl layered double hydroxides and tryptophan

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 0.25xa0molxa0L−1 Trp ethanol/water solutions, respectively. IR spectra showed that bands attributed to Trp appeared as the Tb-LDH reacted with 0.10 and 0.25xa0molxa0L−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.

Intercalation of cytosine into Eu 3+ -doped hydrocalumite and their fluorescent responses

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.

Structure and photoluminescence of a novel red-emitting phosphor Ca 12 Al 14-x Eu x O 32 Cl 2 prepared by phase transition

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 600xa0°C for 2xa0h. The crystallinity of the Ca12Al14-xEuxO32Cl2 phase gradually improved with temperature up to 800 and 1000xa0°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 1000xa0°C, respectively. The Ca12Al14-xEuxO32Cl2 phase can be efficiently excited by near ultraviolet light and shows strong red-orange emissions at 618 and 589xa0nm, due to 5D0-7F2 and 5D0-7F1 transition of Eu3+, respectively. The strongest red-orange emissions appeared in the sample annealed at 600xa0°C. The present Ca12Al14-xEuxO32Cl2 may be a promising candidate for cheap and high efficiency red-emitting phosphors applied in LEDs.