Transition Rare Earth Ions Research Articles

Lithium‐Lanthanide Heterometallic Organic Frameworks with Near‐Unity Photoluminescence Quantum Yields for Single‐Composition White‐Light Emission and Fluorescent Sensing on Nitrobenzene

AbstractLanthanide ion contained metal–organic frameworks (MOFs) have garnered significant attention in the fields of solid‐state lighting and chemical sensing due to their porous structure and distinctive optical properties. However, they also present challenges because of the limited photoluminescence (PL) intensity resulting from the parity‐forbidden f–f transitions of lanthanide ions. Herein, the study reports a new heterometallic MOFs Ln3Li2L4 (Li‐Ln‐MOF, Ln = Y, Eu, Tb and Dy, L = deprotonated 1,3,5‐tris(4‐carboxyphenyl)benzene) with a Brunauer‐Emmett‐Teller (BET) surface area of 774.1 m2/g. The porous crystal structure of Li‐Ln‐MOF is characterized by three kinds of channels interpenetrating with each other. By employing ligand alternation and lanthanide ion alloying strategies, Li‐Y1‐xEux‐MOF1 crystal isostructural with Li‐Ln‐MOF is synthesized by using 2,4,6‐tris(4‐carboxyphenyl)‐1,3,5‐triazine (H3TATB) as ligand. The Li‐Y0.7Eu0.3‐MOF1 crystal excels in the comprehensive performance with a BET surface area of 858.8 m2 g−1 and a near‐unity PL quantum yield. The time density functional theory and natural transition orbitals calculations unravel that the outstanding optical properties Li‐Y0.7Eu0.3‐MOF1 originates from the charge transfer between TATB3− and Eu3+. Benefiting from the excellent comprehensive performance of Li‐Y1‐xEux‐MOF1, the study reveals their potentials as single‐composition white‐light emission and fluorescent sensing probe for the detection of nitrobenzene.

Characterization of Ce3+ and Eu3+ doped and co-doped ZnO nanoparticles for luminescence applications

This paper investigates the synthesis of Ce3+ and Eu3+ doped, as well as co-doped ZnO nanoparticles using the solution combustion route. The nanoparticles exhibit a hexagonal wurtzite structure of ZnO with crystallite sizes ranging from 19 to 22 nm. Structural parameters, including lattice constants, bond lengths, and bond angles, are evaluated. Morphological diversity is observed in field-emission scanning electron microscopy images. The diffuse reflectance spectroscopy results reveal an energy band gap of 3.20 eV for undoped ZnO nanoparticles. The energy band gap value slightly decreases for Eu-doped ZnO and certain (Ce, Eu) co-doped ZnO nanoparticles. Photoluminescence (PL) excitation peaks are attributed to energy levels of native defects in the ZnO band gap, along with f–d and f–f transitions of rare-earth ions (Ce3+, Eu3+). The PL emission spectra under different excitation wavelengths (350 nm, 394 nm, and 465 nm) display varied peak positions. ZnO co-doped with 0.96 mol% of Ce3+ and 0.92 mol% of Eu3+ emerges as a promising material for luminescence applications, exhibiting a significant increase in green emission intensity. Consequently, this study represents a novel contribution to the field of ZnO-based luminescent materials.

Toward radiative-limited coherence of erbium dopants in a nanophotonic resonator

Atomic-like emitters in the solid state serve as important resources in the advancement of future quantum networks. In particular, intra-4f optical transitions of rare earth ions exhibit excellent coherence properties thanks to the shielding effect of outer electrons. Still, the presence of various dephasing channels in solid state hosts introduces additional decoherence beyond the radiative decay, causing the coherence time of most rare earth doped materials to be over an order of magnitude lower than the radiative limit. Such obstacle prevents the emission of indistinguishable photons from rare earth ions, which is an essential requirement for various quantum applications. In this work, we perform optical coherence study on erbium ions doped in thin-film lithium niobate by patterning photonic crystal resonators with quality factor around 100 k and sub-λ3 mode volume. Leveraging the combination of long coherence and strong Purcell enhancement in the cavity, we show that the coherence time measured with photon echo approaches the radiative limit (80%), representing a 50-fold improvement compared to the waveguide case. Our results present promising prospects toward utilizing rare earth doped materials as quantum repeaters and sources of indistinguishable photons.

Dual excitable upconversion nanoparticle@polydopamine nanocomposite with intense red emission and efficient photothermal generation

Integration of strong upconversion emission with deep tissue penetration and stable photothermal generation is of great significance for imaging-guided photothermal therapy under infrared excitation. Herein, the NaYF4:Yb3+,Ho3+,Ce3+@NaGdF4:Yb3+,Nd3+@NaGdF4 core-shell-shell upconversion nanoparticles (UCNPs) with increasing Ce3+ doping concentration were firstly synthesized, in which the size manipulation, enhanced red to green emission intensity ratio (IR/IG), 980 and 808 nm dual-modal excitations, as well as improved total upconversion emission intensity can be achieved. After the coating of polydopamine (PDA) through dopamine spontaneous polymerization on the UCNPs surface under alkaline condition, the obtained UCNP@PDA nanocomposites show efficient photothermal effect under 808 nm excitation, while the thickness variation of PDA can be indicated by the upconversion spectra under 980 nm excitation. Interestingly, the photothermal effect of the UCNP@PDA nanocomposites with high IR/IG ratio is more stable with PDA thickness variation, which benefits from the structure design that allows PDA to simultaneously absorb the visible emission from inside UCNPs and the external 808 nm infrared light. Further in vitro cytotoxicity assay and photothermal therapy demonstrate that the UCNP@PDA nanocomposite has good biocompatibility and ability to kill tumor cells by photothermal effect under 808 nm excitation. This research may provide a nanoplatform for integrating deep bioimaging with highly stable photothermal therapy without the sacrifice of radiative transitions of rare earth ions.

Fine structure of 4f–5d absorption spectra of Me[formula omitted]-Yb[formula omitted] in the vacuum ultraviolet region under synchrotron excitation

Narrow dips were found in the excitation spectra of crystals of alkaline earth fluorides doped with ErF3 or/and YbF3. The positions of the dips are in good agreement with the positions of the narrow absorption lines Er3+, Yb3+ measured earlier. The absorption lines of the crystals were calculated from the excitation spectra. The observed dips in the excitation spectra are due to the absorption lines of 4f–5d transitions in lanthanide ions.

Effect of Er3+ ions on the structural, optical and Judd-Ofelt (JO) intensity parameters of (Bi2O3-BaTiO3) glass system and their application as fiber-amplifier

Barium titanate-based bismuthate glasses doped with Er3+ ions have been fabricated by employing the conventional melt quench technique. Various characterization studies have been performed on the samples for their physical, structural and optical analysis such as the density and molar volume measurements, X-Ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, and UV–Vis spectroscopies. The amorphous nature of the prepared glass samples has been confirmed by the broad humps observed in the X-Ray diffractograms. The FTIR spectra confirmed an increment in the non-bridging oxygen atoms (NBOs) and also the transformation of [BiO6] units to [BiO3] pyramidal units in the structural network of the glass matrix. Raman spectra in the high-frequency region have also been recorded which provided information related to the structural changes in the glass system upon the building of Er-O linkages. Absorption spectra of UV–Vis spectroscopy depicted six transition states such as 4F7/2, 2H11/2, 4S3/2, 4F9/2, 4I11/2, and 4I13/2. The spectroscopic and optical parameters such as energy band gap, optical conductivity, penetration depth, Judd-Ofelt (JO) parameters, refractive index, dielectric constant, Urbach energy, and transmission coefficient for the glasses have been determined, among others. The nephelauxetic ratio (β) and bonding parameters (δ) obtained from transitions of rare-earth ions have revealed the ionic character of the glasses. The calculated values of indirect and direct energy bandgap (Eg) of the prepared samples have been found to decrease from 2.04 to 1.93 and 2.67 to 2.45 resp. on increasing Er3+ ions. Judd-Ofelt (JO) parameters follow the order given by Ω2> Ω6> Ω4 and have been consistent with the literature. A decrement in the values of Ω2 from 3.761 to 2.699, confirmed the lowest asymmetry in the crystal field of rare-earth ions of glass system. The obtained values of refractive index, Urbach energy, dielectric constant, electronic & ionic polarizability and the metallization criterion suggest that the presently studied glass samples are amorphous semiconducting, optically non-linear and are suitable for the applications in erbium-doped fiber-amplifier (EDFA), lasers and optoelectronic devices.

High performance FIR thermometry on the basis of the redshift of CTB by dual-wavelength alternative excitation in Eu3+:YVO4.

Compared with the forbidden 4f transition of rare earth ions, the strong absorption of the charge transfer band (CTB) enabled fluorescence thermometry to have high luminescence efficiency. Based on the temperature induced redshift of CTB, a high performance fluorescence intensity ratio (FIR) thermometry performed by dual-wavelength alternative excitation was studied. By way of the rising and falling edges of CTB in Eu3+ doped YVO4, monochrome sensitivity as a function of excitation wavelength was studied in the range of 303-783 K. The excitation wavelength with the highest positive monochrome sensitivity was determined, as well as that with the negative one. The optimum FIR temperature sensing strategy is proposed, and the theoretical highest relative sensitivity (Sr) is calculated to be 1.86% K-1, with the lowest uncertainty (ΔT) of 0.1 K at 783 K.

A review study on the structural and photoluminescence properties of rare earth doped lanthanate ALa2ZnO5 (A = Ca, Sr or Ba) phosphors

Rare earth doped phosphors are gaining much more attention attributed to their wide optoelectronic applications in the solid-state lighting, in fluorescent lamps, solar cells, display devices, temperature sensors etc. The structural and photoluminescent (PL) features of rare earth doped lanthanate compounds ALa2ZnO5 (A = Ca, Sr or Ba) are extensively explored by researchers owing to their better physical, chemical and luminescent properties. This review deals with the study of different methods used for the synthesis of bare and rare earth doped ALa2ZnO5 (A = Ca, Sr or Ba) phosphors. The solution combustion process has proved to be a better low temperature synthesis technique than the alternative methods such as solid state, sol-gel and co-precipitation methods etc. to get highly crystalline lanthanate phosphors. Structural analysis is also studied in detail to understand the different phases of rare earth doped CaLa2ZnO5, SrLa2ZnO5 and BaLa2ZnO5 phosphors. Apart from this, the PL properties of these rare earth doped lanthanate compounds are explained in depth. Their excitation, emission wavelength, lifetime and CIE coordinates are also provided for comparative studies along with their applications. Owing to the significant number of energy transitions of rare earth ions within the host lattice, these lanthanate phosphors have wide scope in different display fields. The reading of this review will be beneficial for researchers working in the field of phosphors.

Fluoroindate glasses co-doped with Pr3+/Er3+ for near-infrared luminescence applications

Fluoroindate glasses co-doped with Pr3+/Er3+ ions were synthesized and their near-infrared luminescence properties have been examined under selective excitation wavelengths. For the Pr3+/Er3+ co-doped glass samples several radiative and nonradiative relaxation channels and their mechanisms are proposed under direct excitation of Pr3+ and/or Er3+. The energy transfer processes between Pr3+ and Er3+ ions in fluoroindate glasses were identified. In particular, broadband near-infrared luminescence (FWHM = 278 nm) associated to the 1G4 → 3H5 (Pr3+), 1D2 → 1G4 (Pr3+) and 4I13/2 → 4I15/2 (Er3+) transitions of rare earth ions in fluoroindate glass is successfully observed under direct excitation at 483 nm. Near-infrared luminescence spectra and their decays for glass samples co-doped with Pr3+/Er3+ are compared to the experimental results obtained for fluoroindate glasses singly doped with rare earth ions.

Quantum Point Defects for Solid-State Laser Refrigeration.

Herein, the role that point defects have played over the last two decades in realizing solid-state laser refrigeration is discussed. A brief introduction to the field of solid-state laser refrigeration is given with an emphasis on the fundamental physical phenomena and quantized electronic transitions that have made solid-state laser-cooling possible. Lanthanide-based point defects, such as trivalent ytterbium ions (Yb3+ ), have played a central role in the first demonstrations and subsequent development of advanced materials for solid-state laser refrigeration. Significant discussion is devoted to the quantum mechanical description of optical transitions in lanthanide ions, and their influence on laser cooling. Transition-metal point defects have been shown to generate substantial background absorption in ceramic materials, decreasing the overall efficiency of a particular laser refrigeration material. Other potential color centers based on fluoride vacancies with multiple potential charge states are also considered. In conclusion, novel materials for solid-state laser refrigeration, including color centers in diamond that have recently been proposed to realize the solid-state laser refrigeration of semiconducting materials, are discussed.

Giant spin-noise gain enables magnetic resonance spectroscopy of impurity crystals

Spin noise spectroscopy is a method of magnetic resonance widely used, nowadays, in atomic and semiconductor research. Classical objects of the EPR spectroscopy - dielectrics with paramagnetic impurities - seemed to be unsuitable for this technique because of large widths of allowed optical transitions and, therefore, low specific Faraday rotation (FR). We show, however, that the FR noise detected at the wavelength of a weak optical transition (with low regular FR) may increase by many orders of magnitude as its homogeneous width decreases. This spin-noise gain effect, numerically described by the ratio of the inhomogeneous linewidth to homogeneous, relates primarily to forbidden intraconfigurational transitions of impurity ions with unfilled inner electronic shells. Specifically, for the f-f transitions of rare-earth ions in crystals, this factor may reach 10$^8$. In this paper, we report on the first successful application of spin noise spectroscopy for detecting magnetic resonance of rare-earth ions in crystals.

Controlling the color with different excitations in a dysprosium-activated apatite oxynitride phosphor

Among the f-f transition of lanthanide ions, trivalent dysprosium (Dy3+) activated luminescence materials always exhibit polychromatic emission with different ratios of blue to yellow emission (B/Y ratio), which originates from the two main transitions 4F9/2 to 6H15/2 and 6H13/2, respectively. Researchers have found the B/Y ratio is dependent on the host structure. Meanwhile, Dy3+-activated luminescence materials have various applications under different excitations. However, the relationship between them (excitation vs emission color) has not been studied yet, which restricts the development of fundamental research and applications. In this study, we reported an excitation-controlled color variation material, the apatite oxynitride phosphor Y5Si3O12N: Dy3+ and investigated the color-reversal phenomenon by switching excitation sources (from UV to VUV or cathode ray) in the material. This phenomenon is unraveled by a defect-assisted charge carrier transport model that the defect could change the chemical surrounding of Dy3+ and result in the blue emission dominant instead of the initial yellow emission. The mechanism is evidenced by the crystal structure analysis, luminescence properties dissect, defects state parse, etc. This study also provides new insights to understand and modulate Dy3+-activated luminescence materials.

Terahertz spectroscopic characterization of spin mode and crystal-field transition in high-throughput grown <inline-formula><tex-math id="Z-20201027023844-1">\begin{document}$ {\bf Sm}_{ x}{\bf Pr}_{ 1– x}{\bf FeO_3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20200732_Z-20201027023844-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="20-20200732_Z-20201027023844-1.png"/></alternatives></inline-formula> crystals

Terahertz (THz) transient has become an effective method to study the optical and electronic spin characteristics of the rare earth orthoferrites <i>R</i>FeO<sub>3</sub>. High-throughput grown crystal sample is sliced at different locations, then the continuously tunable rare earth elements co-doped single crystal Sm<sub><i>x</i></sub>Pr<sub>1–<i>x</i></sub>FeO<sub>3</sub> is studied with antiferromagnetic spin mode (qAFM) and crystal field transitions of rare earth ions under zero magnetic fields. Using THz time-domain spectroscopy, the qAFM resonance frequencies of Sm<sub>0.2</sub>Pr<sub>0.8</sub>FeO<sub>3</sub> and Sm<sub>0.4</sub>Pr<sub>0.6</sub>FeO<sub>3</sub> single crystals are located on the connection line of the qAFM frequencies of PrFeO<sub>3</sub> (0.57 THz) and SmFeO<sub>3</sub> (0.42 THz), therefore the frequency of qAFM increases linearly with doping concentration of Sm<sup>3+</sup> ion increasing. The Sm<sub>0.4</sub>Pr<sub>0.6</sub>FeO<sub>3</sub> crystal undergoes a temperature-induced spin reorientation phase transition at about 160 K. When the crystal temperature is lower than 80 K, a wide band absorption peak of about 0.5 THz appears in the absorption spectrum of Sm<sub>0.2</sub>Pr<sub>0.8</sub>FeO<sub>3</sub> due to the crystal field effect. Our results show that THz spectral data not only allow us to monitor the quality of rare earth orthoferrite crystals prepared by high throughput and analyze the rare earth elements of the sample, but also improve the ability to analyze the physical properties of the co-doped <i>R</i>FeO<sub>3</sub>.

Photoluminescence and piezoelectricity investigation of La1.98Nd0.02Ti2O7, Sm1.98Ce0.02Ti2O7 and Er1.98Gd0.02Ti2O7 multifunctional materials

Abstract Nd3+ doped La2Ti2O7, Ce4+ doped Sm2Ti2O7 and Gd3+ doped Er2Ti2O7 have been synthesized at different reaction temperatures using solid state reaction method, and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), thermogravimetric analysis (TG). Excitation spectra, emission spectra and decay time curves of the samples were investigated by photoluminescence spectrophotometer (PL) and typical transitions of rare earth ions were observed. Dielectric properties, piezoelectric properties and Curie temperature of the obtained luminescent materials were measured for electrical characterization. The results showed that all materials have both photoluminescent and piezoelectric properties and show high Curie temperature.

Rare-Earth and Antimony-Oxo Clusters Simultaneously Connecting Antimonotungstates Comprising Divacant and Tetravacant Keggin Fragments.

Four novel rare-earth (RE) and Sb-oxo clusters simultaneously bridging antimonotungstates (ATs) [H2N(CH3)2]8Na6H8{[RE4(H2O)6Sb6O4](SbW10O37)2(SbW8O31)2}·24H2O [RE = Dy3+ (1), Er3+ (2), Y3+ (3), Ho3+ (4)] were triumphantly isolated by using Na9[B-α-SbW9O33]·19.5H2O, dimethylamine hydrochloride, SbCl3, and RE(NO3)3·6H2O in acidic aqueous solution. Their tetrameric polyoxoanions are all established by two [SbW10O37]11- and two [B-α-SbW8O31]11- segments encapsulating a RE-Sb heterometal [RE4(H2O)6Sb6O4]22+ cluster. Under the O→W LMCT excitation at 268 nm of AT segments, RE ions in 1 and 2 can absorb the 3T1u→1A1g emission energy of AT segments, giving rise to the sensitization of AT segments to the emission of RE ions. Through the sensitization of AT segments, the emission intensities of RE ions in 1 and 2 are increased and lifetimes are prolonged. Photoluminescence and energy transfer measurements indicate that Dy3+ ions in 1 can obtain more energy from AT segments than to Er3+ ions in 2. Furthermore, the sensitization effects of AT segments to different f-f transitions of RE ions have been compared in 1 and 2. Under the sensitization of AT segments, the 4F9/2→6H15/2 transition obtains the most energy compared with the 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions in 1, and the 2H11/2→4I15/2 transition obtains more energy than the 4S3/2→4I15/2 transition in 2. It seems that the better energy level match of 3T1u→1A1g transition of AT segments with f-f emission transitions of RE ions will lead to a stronger sensitization effect.

Effect of acceptor ions concentration in lead phosphate glasses co-doped with Tb3+–Ln3+ (Ln = Eu, Sm) for LED applications

In this work, lead phosphate glasses doubly doped with Tb3+ and Ln3+ (Ln = Eu, Sm) ions were prepared. The excitation and emission spectra of lanthanides ions were recorded. The luminescent properties of lead phosphate glasses containing various concentrations of acceptor ions were analyzed. It is observed that luminescence bands corresponding to characteristic transitions of rare earth ions are present on emission spectra measured under direct excitation of Tb3+. From the emission spectra, the Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x, y) were calculated in relation to potential application studied systems for white LEDs. Luminescence lifetimes were also determined based on decay measurements and discussed in details. In general, the luminescence spectra and luminescence lifetimes depend on the relative concentrations of the optically active dopants.

Mn2+-activated calcium fluoride nanoprobes for time-resolved photoluminescence biosensing

Time-resolved (TR) photoluminescence (PL) technique has shown great promise in ultrasensitive biodetection and high-resolution bioimaging. Hitherto, almost all the TRPL bioprobes are based on the parity-forbidden f→f transition of lanthanide ions. Herein, we report TRPL biosensing by taking advantage of the d→d transition of transition metal (TM) Mn2+ ion. We demonstrate that the Forster resonance energy transfer (FRET) signal can be distinguished from that of radiative reabsorption process through measuring the PL lifetime of Mn2+, thus establishing a reliable method for Mn2+ in homogeneous TR-FRET biodetection. We also demonstrate the biotin receptor-targeted cancer cell imaging by utilizing biotinylated CaF2:Ce,Mn nanoprobes. Furthermore, we show in a proof-of-concept experiment the application of the long-lived PL of Mn2+ for TRPL bioimaging through the burst shot with a cell phone. These findings provide a general approach for exploiting the long-lived PL of TM ions for TRPL biosensing, thereby opening up a new avenue for the exploration of novel and versatile applications of TM ions.

Optical spectroscopy of molybdates with composition Ln2Zr3(MoO4)9 (Ln: Eu, Tb)

This study examined the luminescent properties of systems of double molybdates doped with Eu and Tb — this includes emission, excitation and absorption spectra. The compounds exhibited bright luminescence in the visible region due to the [Xe]4fn → [Xe]4fn transitions of rare-earth ions. The luminescence is excited both in the [Xe]4fn → [Xe]4fn bands of the rare-earth ions and in the wide band in the ultraviolet region related to the transitions within the Mo-O complex. Because of the energy transfer, the luminescence of Tb3+ and Eu3+ in doubly doped molybdates has had common excitation energies.

Highly Efficient Blue Emission and Superior Thermal Stability of BaAl12O19:Eu2+ Phosphors Based on Highly Symmetric Crystal Structure

Highly efficient phosphor materials with superior thermal stability are indispensable for phosphor-converted white light-emitting diodes (pc-WLEDs) solid state lighting. In order to obtain a high quality warm white light, near-ultraviolet (n-UV) chips combined with trichromatic phosphors have be extensively studied. Among them, the development of efficient blue phosphor remains a challenging task. In view of the close correlation between 5d–4f transitions of rare earth ions and the coordination environment of host lattice, many studies have been dedicated to improving the photoluminescence performances by modifying the lattice coordination environment including the lattice rigidity and symmetry. In this work, we reported highly efficient blue-emitting Eu2+-doped BaAl12O19 (BAO) phosphors with excellent thermal stability, which were prepared via the traditional high-temperature solid state reaction routes. According to the X-ray powder diffraction (XRD) Rietveld refinement analysis, BAO owned a highly symm...

Tunable emission in Ln3+ (Ce3+/Dy3+, Ce3+/Tb3+) doped KNa3Al4Si4O16 phosphor synthesized by combustion method

Ln3+ (Ln = Ce3+/Dy3+, Ce3+/Tb3+) doped KNa3Al4Si4O16 phosphor has been synthesized by Combustion method (CS) at 550° C successfully. Ln3+ (Ln = Ce3+, Dy3+, Tb3+) ions when doped in KNa3Al4Si4O16 host lattice, it shows blue and green emission band under the near Ultraviolet (NUV) excitation wavelength. The Photoluminescence excitation (PLE) and emission spectra are observed due to f-f and d-f transition of rare earth ions. Also, an effective energy transfer (ET) study from Ce3+ → Dy3+ and Ce3+ → Tb3+ ions has been studied and confirmed on the basis of Dexter-Foster theory. Further synthesized phosphor is well characterized by XRD, SEM, TEM and decay time measurement. However, the analysis of crystallite size, lattice strain has been studied by using theoretical as well as experimental techniques. Hence, the observed tunable emission in Ln3+ doped KNa3Al4Si4O16 phosphor may be applicable for solid state lighting technology.