Rare Earth Luminescent Materials Research Articles

Photo-conversions in Ho3+/Yb3+ co-doped pairs under pulsed high magnetic fields

Abstract The optical up-conversion and down-conversion (or quantum cutting) processes in Ho 3 + / Yb 3 + co-doped YVO 4 and GdVO 4 crystals, particularly cross relaxation and emission channels, were investigated with the help of magnetic fields. Cross-relaxation and emission channels were addressed with the help of magnetic field. The results demonstrated that cross relaxation processes between the donor Ho 3 + ( Yb 3 + ) ions and acceptor Yb 3 + ( Ho 3 + ) ions play positive roles in up-conversion, but negative roles in quantum cutting transitions. In addition, the conversion efficiency of the co-doped pairs depended on the hosts though could be distinctively modulated by a magnetic field. The results are helpful in understanding cross-relaxation processes and identifying the emissions originating in bi- (multi-) rare earth ion-doped luminescent materials, and also helpful in improving their efficiency in application.

Controlling multiphoton excited energy transfer from Tm3+ to Yb3+ ions by a phase-shaped femtosecond laser field

The ability to control the energy transfer in rare-earth ion-doped luminescent materials is very important for various related application areas such as color display, bio-labeling, and new light sources. Here, a phase-shaped femtosecond laser field is first proposed to control the transfer of multiphoton excited energy from Tm3+ to Yb3+ ions in co-doped glass ceramics. Tm3+ ions are first sensitized by femtosecond laser-induced multiphoton absorption, and then a highly efficient energy transfer occurs between the highly excited state Tm3+ sensitizers and the ground-state Yb3+ activators. The laser peak intensity and polarization dependences of the laser-induced luminescence intensities are shown to serve as proof of the multiphoton excited energy transfer pathway. The efficiency of the multiphoton excited energy transfer can be efficiently enhanced or completely suppressed by optimizing the spectral phase of the femtosecond laser with a feedback control strategy based on a genetic algorithm. A (1+2) resonance-mediated three-photon excitation model is presented to explain the experimental observations. This study provides a new way to induce and control the energy transfer in rare-earth ion-doped luminescent materials, and should have a positive contribution to the development of related applications.

Synthesis of high crystalline hierarchical self-assembled MMoO4 (M=Ca, Sr and Ba) super structures: Having hydrophilic surfaces and obvious red-shifted photoluminescence behavior

Abstract Three-dimensional (3D) hydrophilic surfaced MMoO4 (M = Ca, Sr and Ba) superstructures were successfully synthesized using a surfactant-assisted hydrothermal route. This green chemistry method by use of inexpensive reagents makes procedure simple and highly reproducible. The prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), emission/excitation spectra analyses, and Fourier transform infrared (FT-IR), Raman, and ultraviolet–visible (UV–Vis) spectroscopies. The scanning electron microscope (SEM) studies demonstrated that the optimized material can be synthesized at pH 6 and 180 °C for CaMoO4 and pH 5 and 220 °C for SrMoO4. Prepared materials displayed good dispersion of small-sized gold and the product consisted of a large number of doughnut and sphere-like superstructures for CaMoO4 and SrMoO4, respectively. The result showed that the mean diameters of doughnut and sphere-like particles were about 2.5–5 μm and 2.5 μm, respectively and the as-synthesized self-assembled superstructures were composed of nanosheets with the thickness of about 20–50 nm. Also, the SEM micrographs demonstrate that the morphology of the optimized materials for BaMoO4, synthesised at 200 °C and pH 5, were particles with hierarchical self-assembled architecture that composed of very long central stems with an average length of about 20–40 μm in which perpendicular branches was seen. The luminescence properties of the optimized samples with various morphologies have also been investigated and photoluminescence spectra of the samples showed very obvious red-shifted PL emission without using rare earth ions-doped luminescent materials and the energy transfer process from host to rare earth ions.

Hydrothermal Preparation of Five Rare-Earth (Re = Dy, Gd, Ho, Pr, and Sm) Luminescent Cluster-Based Coordination Materials: The First MOFs-based Ratiometric Fluorescent Sensor for Lysine and Bifunctional Sensing Platform for Insulin and Al3.

Through the powerful hydrothermal method, five rare-earth (Re = Dy, Gd, Ho, Pr, and Sm) three-dimensional (3D) cluster-based metal-organic frameworks (MOFs) have been synthesized, namely, [Dy(L)(H2O)(DMF)] n (1), {[Gd(L)(H2O)(DMF)]·DMF} n (2), {[Ho(L)(H2O)(DMF)]·0.5DMF} n (3), {[Pr(L)(H2O)(DMF)]·0.5DMF} n (4), and {[Sm(L)(H2O)1.55(DMF)0.45]·DMF} n (5; H3L = terphenyl-3,4″,5-tricarboxylic acid), which have been determined by single crystal X-ray analyses and PXRD characterization. Structural analyses reveal that, in 1-5, these L3- ligands are linked by five different rare-earth centers, forming the iso-structural nanoporous frameworks. PXRD patterns of bulky samples 1-5 also are consistent with theoretical PXRD patterns confirming their purity. Solid state photoluminesce of free H3L and 1-5 at room temperature also has been investigated indicating strong ligand-based emissions. Besides these, fluorescent dye Rhodamine B (RhB) can be introduced into MOF1 forming the composite material RhB@MOF1 with a high quantum yield of 35%. It is noted that, through deliberately tuning the morphologies of nanoparticle MOF1 under different ultrasonic conditions, RhB@MOF1 can be utilized as the first ratiometric fluorescent sensor to effectively discriminate l- and d-lysine from other amino acid molecules with high Ksv values and low LOD values. On the other hand, 2 was for the first time to be utilized as an excellent bifunctional MOFs-based sensing platform to detect insulin and Al3+ with a low detection limit in the human serum solution.

Lanthanide complexes-functionalized ordered mesoporous TiO2: Multicolor emission (visible and near-infrared luminescence) based on visible-light sensitization

Abstract Recently, much attention has been paid to the lanthanide luminescent materials based on the visible-light sensitization for their potential applications in the fields of bio-imaging and optical devices. In this work, the lanthanide complexes have been covalently bonded to the ordered mesoporous titania (OMT) matrix, and the resulting titania-based hybrid ordered mesoporous materials (named as LnDB-OMT, Ln = Eu, Sm, Yb, Nd) were characterized by using Fourier-transform infrared (FT-IR) spectroscopy, small-angle X-ray powder diffraction (SAXD), N2 adsorption–desorption isotherms, transmission electron microscopy (TEM), fluorescence spectroscopy, and thermogravimetric analysis. Generally, exciting with visible light is advantageous over UV excitation. Of importance here is that, under excitation with visible light, the LnDB-OMT all show characteristic visible (Eu3+, Sm3+) as well as near-infrared (Sm3+, Yb3+, Nd3+) luminescence of the corresponding Ln3+ ions (multicolor emission covered from 500 to 1400 nm spectral region), which is attributed to the energy transfer from the ligands to the Ln3+ ions via an antenna effect.

Study on the light-color mixing of rare earth luminescent materials for anti-counterfeiting application

In order to find out the light color mixing mechanism of rare earth luminescent materials used in anti-counterfeiting fibers, we prepared three kinds of rare earth luminescent materials according to RGB tri-primary color, and mixed it together to form different mixtures in certain proportion. The phase structures of the luminescent material monomers were measured by x-ray diffractometer. The photochromic properties of the luminescent materials were tested and analyzed by fluorescence spectrophotometer. The results show that the light color mixing was consistent with the blending principle of additive color, but not the same because of the photochromic properties of rare earth luminescent materials, and we explored the reasons in the light wavelength and intensity. It was found that the enhancement of the luminescence intensity of the mixture on account of the superimposing of luminescence.

Red, White and Blue Light Emission from Europium Doped Al2O3 Confined into a Silica Matrix

The main drawbacks of fluorescent activated lanthanide luminescent materials in practical optoelectronic applications are the high cost of raw material and the limitation of a specific color depending on the lanthanide ion. In this work, the synthesis of red, white and blue light emitting composite powders of Al2O3:Eu3+@SiO2 were successfully synthesized by the hydrolysis and condensation reactions of TEOS as the raw precursor of silica matrix on the Al2O3:Eu3+ surface. With the aim to change the CIE coordinates different weight ratios of Al2O3:Eu3+/SiO2 powders from 13Al/87Si to 5Al/95Si were prepared. Besides, various excitation wavelength from 280 to 340 nm was used in order to change the ratio intensity; Ired/Iblue, between the red emission coming from the 5D0→7F2 transition of Eu3+ ions and the blue band of silica matrix. Chemical evolution of the hydrolysis and condensation reaction of TEOS were conducted by FTIR spectroscopy. The results indicate that from 500°C a complete TEOS to SiO2 transformation is carried out.

Thermosensitive luminous fibers based on cresol red-boric acid reversible thermochromic pigments

In this study, thermosensitive luminous fibers (TLFs) were prepared by wet spinning, using polyacrylonitrile as the filament material and rare-earth long-afterglow luminescent materials as the optical source. Reversible thermochromic cresol red-boric acid (CB) pigment in the TFLs served as the luminescence conversion agent. The reflectivity curves and fluorescence spectra were recorded at 25 and 65 °C to investigate the thermosensitive characteristics of the TLFs. The results demonstrated that CB pigment functioned as a luminescent conversion agent that could convert the luminescence of rare-earth luminescent materials depending on the temperature. The luminescence of the TLFs can be converted from blue to fuchsia upon changing their temperature due to the structural transformation of the CB dye. The thermosensitivity can also be verified by observing the TLFs in water at 65 °C with the naked eye.

Morphology-controlled synthesis, growth mechanism and fluorescence of YF3:Eu3+, Bi3+

Abstract In recent years, morphology-controlled synthesis and corresponding property tuning in inorganic materials have attracted considerable attention. In this work, lanthanide luminescent materials of YF 3 :0.125Eu 3+ , 0.5%Bi 3+ with a variety of well-defined morphologies including spherical, truncated octahedron, octahedron and pseudo-sphere particle have been controllably synthesized via a facile hydrothermal method. Phase structure and morphology of the materials are tuned, and thus fluorescent properties are tailored by changing the synthetic parameters of reaction temperature and dwelling time. With increasing reaction temperature, the materials are transformed from KY 3 F 10 to YF 3 , and the morphology varies from spherical to octahedron and finally truncated octahedra. When dwelling time increases, the samples also extend from KY 3 F 10 to YF 3 and the morphology changes from spherical to octahedron, then truncated octahedra and finally pseudo-sphere particle. The possible growth mechanism for diverse morphologies has been proposed. The fluorescence intensity of the materials is closely related to their morphologic characteristics. The YF 3 :0.125Eu 3+ , 0.5%Bi 3+ with truncated octahedra synthesized at 200 °C for 18 h presents the strongest emission intensity because of its less defects sites and large grain size. In addition, it has been demonstrated that the present luminescent materials can be potentially used as the luminescent ink.

Thermosensitive luminous fiber based on reversible thermochromic crystal violet lactone pigment

The aim of this work is to investigate the luminescence color changes of thermosensitive luminous fibers (TLFs). These TLFs are comprised of rare-earth luminescent materials as the luminescence sources, reversible thermochromic crystal violet lactone (CVL) pigment as the luminescence conversion agent, and polyacrylonitrile (PAN) as the matrix. It was found that the TFLs could not only change their color, but also convert the luminescence upon temperature change based on a structural transformation of the CVL pigment. X-ray diffraction (XRD) measurements indicated that rare-earth luminescent materials maintained their basic crystal structure and the CVL pigment was not destroyed by the process of spinning. The scanning electron microscopy (SEM) images of TLFs at the microcosmic angle showed that the CVL pigments were evenly distributed in the PAN matrix and formed a luminescence filter on the surface of the fiber. The differential scanning calorimetry (DSC) and thermogravimetry (TGA and DTG) results indicate that the TLFs possess satisfactory thermostability below 212.6 °C. The color and luminescence of the TLFs were accurately exhibited on the CIE 1931 chromaticity coordinates. The thermosensitive capability of TLFs was qualitatively verified by observing them in water at 40 °C and it was found that the fibers had brilliant luminescence and vivid thermosensitivity.

Synthesis of monodispersed hierarchical Yb(OH)xF3−x microcrystals and their conversion to Yb6O5F8

Abstract The fabrication of rare earth luminescent materials with monodispersed and hierarchical morphology is of great importance due to their various applications. In this report, monodispersed hierarchical Yb(OH) x F 3−x microcrystals assembled by nanorod arrays were synthesized by a mild hydrothermal route. Calcination of Yb(OH) x F 3−x resulted in the formation of Yb 6 O 5 F 8 with the retention of morphology. The crystallographic structure relationship between Yb(OH) x F 3−x and Yb 6 O 5 F 8 and the transformation mechanism from Yb(OH) x F 3−x to Yb 6 O 5 F 8 were disclosed. The upconversion emission properties of the Er 3+ doped samples were investigated. It can be found that Yb 6 O 5 F 8 : 5%Er 3+ exhibited an intense red light upconversion emission with the strongest peaks around 658 nm while Yb(OH) x F 3−x : 5%Er 3+ shows no upconversion emission.

Large‐area flexible, transparent, and highly luminescent films containing lanthanide (III) complex‐doped ionic liquids for efficiency enhancement of silicon‐based heterojunction solar cell

ABSTRACTIonic liquid (IL)‐based lanthanide luminescent materials with luminescent downshifting properties are beneficial for enhancing the photovoltaic energy conversion efficiency (ηpv) of silicon‐based solar cells. Herein, novel lanthanide (III) complex‐doped ILs have been successfully prepared by simply dissolving the complex Ln(pybox)3 (Ln = Eu or Tb, pybox = 2,6‐bis[(4R)‐4‐phenyl‐2‐oxazolinyl]pyridine) into a bidentate organophosphine functionalized IL (1,3‐bis‐[3‐(diphenylphosphinyl)propyl]imidazolebis (trifluoromethylsulfonyl)imide), showing improved luminescence efficiency attributed to the coordination of ILs with Ln3+ ions and thus occurrence of the energy transfer from ILs to Ln3+ ions and very high absolute quantum efficiency (up to 97.22%). Large area (17 × 17 cm2) flexible, transparent, and luminescent poly(methyl methacrylate) thin films were prepared through a simple drop‐casting method and were applied as luminescent downshifting coatings to the silicon‐based heterojunction solar cells (active area: 235 cm2). In the best case using the Tb3+‐containing film, the ηpv of the solar cell increases from 16.676 to 16.774%.

Sol–Gel Electrolytes Incorporated by Lanthanide Luminescent Materials and Their Photophysical Properties

A group of silica gel electrolytes with lanthanide luminescent hybrid materials were assembled and investigated. Photophysical studies showed that terbium and europium hybrids displayed characteristic green and red emissions within the electrolytes. The influence of different concentration of the lanthanide hybrids on the electrochemical behavior of a gelled electrolyte valve-regulated lead-acid battery were studied through cyclic voltammograms, electrochemical impedance spectroscopy, water holding experiments and mobility tests. The morphology and particle size were analyzed by scanning electron microscopy. The results proved that lanthanide (Tb3+/Eu3+) luminescent materials are effective additives which will significantly improve the electrochemical properties of lead-acid batteries.

Fabrication and characterization of dual-functional ultrafine composite fibers with phase-change energy storage and luminescence properties

Ultrafine composite fibers consisting of a thermoplastic polyurethane solid-solid phase-change material and organic lanthanide luminescent materials were prepared through a parallel electrospinning technique as an innovative type of ultrafine, dual-functional fibers containing phase-change and luminescent properties. The morphology and structure, thermal energy storage, and luminescent properties of parallel electrospun ultrafine fibers were investigated. Scanning electron microscopy (SEM) images showed that the parallel electrospun ultrafine fibers possessed the desired morphologies with smaller average fiber diameters than those of traditional mixed electrospun ultrafine fibers. Transmission electron microscopy (TEM) images revealed that the parallel electrospun ultrafine fibers were composed of two parts. Polymeric phase-change materials, which can be directly produced and spun, were used to provide temperature stability, while a mixture of polymethyl methacrylate and an organic lanthanide complex acted as the luminescent unit. Differential scanning calorimetry (DSC) and luminescence measurements indicated that the unique structure of the parallel electrospun ultrafine fibers provides the products with good thermal energy storage and luminescence properties. The fluorescence intensity and the phase-change enthalpy values of the ultrafine fibers prepared by parallel electrospinning were respectively 1.6 and 2.1 times those of ultrafine fibers prepared by mixed electrospinning.

Preparation and luminescence studies of thermosensitive PAN luminous fiber based on the heat sensitive rose red TF-R1 thermochromic pigment

Abstract The aim of this study was to prepare and demonstrate a new kind of thermosensitive luminous fiber based on optical interference of thermochromic pigments. The surface morphology of a thermosensitive luminous fiber, containing Sr2ZnSi2O7: Eu2+, Dy3+; Y2O2S: Eu3+, Mg2+, Ti4+; and heat-sensitive rose red TF-R1 thermochromic pigment, was analyzed by scanning electron microscope (SEM). The X-Ray Diffraction (XRD) results revealed the crystal structure of the fiber samples and the synthesized rare-earth luminescence materials. There was no degradation of the crystalline phases in the blend when blending and spinning. The thermodynamic stability and dynamic phase structure were analyzed by Thermal Gravity Analysis (TGA) and Differential Scanning Calorimetry (DSC). This thermosensitive polyacrylonitrile (PAN) luminous fiber was stable below 200 °C. The fluorescence spectra, reflectivity spectra were measured to reveal the phosphorescence and thermochromism, and visual testing was also performed. The phosphorescence colors of the thermosensitive luminous fiber were directly related to the temperature. The prepared fiber samples had a red emission at room temperature, and because of the inner phase transition of the heat-sensitive rose red TF-R1 thermochromic pigment on heating, the fiber samples became colorless with blue light emission. This novel thermosensitive luminous fiber has many potential applications in optical and thermal sensors.

Optical performance study of Sr2ZnSi2O7:Eu2+,Dy3+, SrAl2O4:Eu2+,Dy3+ and Y2O2S:Eu3+,Mg2+,Ti4+ ternary luminous fiber

Abstract In this study, down-conversion fluorescent powder of Sr 2 ZnSi 2 O 7 :Eu 2+ ,Dy 3+ , SrAl 2 O 4 :Eu 2+ ,Dy 3+ and Y 2 O 2 S:Eu 3+ ,Mg 2+ ,Ti 4+ , which were the common three primary colors materials with long afterglow, were synthesized by high temperature solid state method. The blends of rare earth (RE) luminescent materials have been of interest to reinvest the luminescent characteristics of polyethylene terephtahalate (PET) luminous fiber. The scanning electron microscopy (SEM) and an inversion fluorescence microscope were used to characterize the surface morphology and the dispersion of inclusion. Through analysis of microcosmic morphology, three typical dispersions of luminescent particles were summarized. The X-ray diffraction indicated that the phase structure of fiber samples and crystal structure of luminescence materials kept complete after prilling and spinning. From the fluorescence spectra and CIE 1931 coordinates, it could be found that different combinations of luminous fibers were desired to obtain divers colors emission luminous fiber. And the fiber samples were a light sensation which could induct different excitation wavelengths and convert it down to different colors. The afterglow decay curve and its differential curve were summarized indicating the three decay stages. The decay curve and decay rate curve showed that the contents of Sr 2 ZnSi 2 O 7 :Eu 2+ ,Dy 3+ , SrAl 2 O 4 :Eu 2+ ,Dy 3+ and Y 2 O 2 S:Eu 3+ ,Mg 2+ ,Ti 4+ had obvious influence on the afterglow of fiber samples.

Ammonium hydroxide modulated synthesis of high-quality fluorescent carbon dots for white LEDs with excellent color rendering properties

A novel type of aqueous fluorescent carbon dot (CD) was synthesized using citric acid as the only carbon source via an ammonium hydroxide modulated method, providing a blue color gamut. The amino group is considered to be the key factor in the high fluorescence of CDs and a model is established to investigate the mechanism of fluorescence. In addition, white light-emitting diodes (WLEDs) are fabricated by utilizing the prepared CDs and rare earth luminescent materials (SrSi2O2N2:Eu and Sr2Si5N8:Eu) as color conversion layers and UV-LED chips as the excitation light source. The WLEDs produce bright white light with attractive color rendering properties including a color rendering index of up to 95.1, a CIE coordinate of (0.33, 0.37), and a Tc of 5447 K under a 100 mA driven current, indicating that the CDs are promising in the field of optoelectronic devices.

Highly luminescent and stable lyotropic liquid crystals based on a europium β-diketonate complex bridged by an ethylammonium cation.

Soft lanthanide luminescent materials are impressive because of their tunable and self-assembling characteristics, which make them an attractive emerging materials field of research. In this report, novel luminescent lyotropic liquid crystals (LLCs) with four different mesophases have been fabricated by a protic ionic liquid (IL) based europium β-diketonate complex EA[Eu(TTA)4] (EA = ethylammonium, TTA = 2-thenoyltrifluoro-acetone) and an amphiphilic block copolymer (Pluronic P123). The protic IL, ethylammonium nitrate (EAN), was used as both the solvent and linkage to stabilize the doped complexes. Analyses by single-crystal X-ray diffraction for EA[Eu(TTA)4] and Fourier transform infrared spectroscopy for the LLC materials reveal convincingly that the ethylammonium cations establish an effective connection with both the carbonyl group of the β-diketonate ligand and the EO blocks of the amphiphilic block copolymer P123 via strong hydrogen bonding interactions. Due to this, an extremely long decay time of the excited state is obtained in EA[Eu(TTA)4] and excellent photostability of the luminescent LLCs could be achieved. The long-period ordered structures of the luminescent LLCs have been investigated by small-angle X-ray scattering measurements and the best luminescence performance was found in the most organized mesophase. Noteworthy, the LLCs could yield an effective confining effect on the europium complex accompanied by a sizeable elongation of the excited-state lifetime and an enhancement of the energy transfer efficiency, which reaches a remarkably high value of 52.6%. More importantly, the modulated luminescence properties observed in the four mesophase structures offer the potential and powerful possibility for these unique composite LLCs to be used in the fabrication of soft luminescent materials with tunable functions.

Effect of light conversion agent on the luminous properties of rare earth strontium aluminate luminous fiber

In order to investigate the effect of light conversion agent on the luminous properties of rare earth luminous fiber, several kinds of rare earth strontium aluminate luminous fibers containing different light conversion agent were artificially manufactured, using rare-earth strontium aluminate as the rare-earth luminescent material and fiber-forming polymers (for polymer polyethylene terephthalate (PET) example) as a matrix. The morphology and the XRD as well as luminous properties of the resulting samples were characterized. Results from scan electron microscopy (SEM) and X-ray diffraction (XRD) demonstrated that there was no obvious difference between surface of luminous fiber without light conversion agent and the luminous fiber containing light conversion agent. The phase of SrA12O4:Eu2+, Dy3+ in the fiber was not destroyed by the complex manufacturing process and the as-formed luminous fiber consisted of irregular particles. Under ultraviolet excitation, the luminous fiber exhibited a yellow–green and orange–red emission band with a maximum at 520 nm and around 600 nm originating from SrAl2O4:Eu2+, Dy3+ and light conversion agent. Furthermore, the emission colors of luminous fibers could be tuned from yellow–green to orange–red easily by doping different light conversion agent, making the materials have potential application in many areas.

Computer-aided design of luminous fiber embroidered fabric and characterization of afterglow performance

Luminous fiber embroidered fabric with a long afterglow effect is prepared by luminous fiber through a computer-aided embroidery machine. As the main raw material, rare earth luminescent material and polymer are used to produce the luminous fiber by the melt spinning process. In this research, the light-emitting portion of the fabric, which uses the principle of superposition of light, is designed by multi-layer construction in computer-aided design software. The afterglow performance of the designed fabric has been characterized. As a result, the size of stitch spacing is inversely proportional to the afterglow intensity of the fabric, and the fabric with a tatami needle has the maximum afterglow intensity in this experiment. Compared to the fabric with non-superimposed stitches in layers, the luminous fabric with superimposed stitches has higher brightness, longer duration of emitting light, and better stable luminescent properties.