Rare Earth Ion Doping Research Articles

Integration of Au Nanosheets and GdOF:Yb,Er for NIR-I and NIR-II Light-Activated Synergistic Theranostics.

The local hyperthermia (>41 °C) effect of photothermal therapy (PTT) is significantly limited by the efficiency of PTT agents to convert laser energy to heat, and such oncotherapy, similar to conventional chemotherapy, invariably encounters the challenge of nonspecific application. Undue reliance on oxygen sources still poses particular difficulties in photodynamic therapy (PDT) for deep-level clinical applications. Considering these therapeutic issues, in this study, we constructed a versatile but unique nanosystem by encapsulating Au nanosheets in codoped gadolinium oxyfluoride (GdOF):Yb,Er spheres, followed by decoration of a chemotherapeutic drug (doxorubicin), photosensitizer (rose Bengal, RB), and targeted agent (folic acid). This allowed the incorporation of cancer treatment and real-time curative efficacy monitoring into one single theranostic nanoplatform. Benefiting from the dual contribution of the strong absorptions in the NIR-I and NIR-II regions, relevant photothermal-conversion efficiency (η) values pertaining to that final product were 39.2% at 1064 nm irradiation and 35.7% at 980 nm illumination. The fluorescence resonance energy transfer that occurred in the up-converted GdOF:Yb,Er to RB contributed to the high PDT efficacy. Combined with a micromeric acid-responsive drug release in a targeted tumor microenvironment, high-performance synergistic therapy was realized. In addition, up-conversion fluorescence imaging and computed tomography imaging accompanied by multimodal magnetic resonance imaging were simultaneously achieved owing to the doped lanthanide ions and the encapsulated Au nanosheets. Our designed oncotherapy nanosystem provides an alternative strategy to acquire ideal theranostic effects.

Mechanisms of rare earth ion distribution in fluorosilicate glass containing KMnF<sub>3</sub> nanocrystal

Luminescent materials with an efficient single-(pure) color up-conversion luminescence (UCL) are expected to be applied to three-dimensional (3D) display, lighting, biological imaging, promoting plant growth and improving the photoelectric conversion efficiency of solar cells. In this work, perovskite-type KMnF<sub>3</sub> fluoride nanocrystals (NCs) are grown in situ in a fluorosilicate glass co-doped with rare earth (RE) ions Yb<sup>3+</sup>/Er<sup>3+</sup> by a controlled thermal treatment. Compared with precursor glass (PG), the nano-glass composites (also referred to as glass ceramics, or GC in short) thus obtained exhibit a significantly enhanced (by 6 times) red UCL emission. Although a weak green UCL emission can be also observed in the GC, the intensity ratio of the red UCL emission to green UCL emission is as high as 30, implying a good color purity. It is suggested that the dramatic enhancement of UCL emissions in the GCs is due to the doping of RE ions into the KMnF<sub>3</sub> NCs with a much lower phonon energy (330 cm<sup>–1</sup>) than that of the silica glass matrix about 1100 cm<sup>–1</sup>. However, the doping mechanisms of RE ions into KMnF<sub>3</sub> nano-glass composites are not yet conclusive, mainly because of the charge and ionic radius mismatch between RE ion dopants and cations of KMnF<sub>3</sub>. This work combines the high-resolution transmission electron microscopy (HR-TEM) analysis technology and the first principles calculation, to unravel the doping mechanism of RE ions in KMnF<sub>3</sub> nano-glass composites. First, the HR-TEM study provides straightforward evidence that RE ions are preferentially accumulated in KMnF<sub>3</sub> NCs embedded in the glass matrix. Then, through the first-principles calculation considering the charge balance, it is found that the formation energy of RE ions substituting for K<sup>+</sup> is lower than for Mn<sup>2+</sup> lattice sites in KMnF<sub>3</sub>, which is most likely related to the fact that the ionic radius of the eight-fold coordinated K<sup>+</sup> is larger than that of the six-fold coordinated Mn<sup>2+</sup> and thus is more conductive to accommodating the large size RE ions. The electronic densities of states at the top of the valence band and the bottom of the conduction band of KMnF<sub>3</sub> increase after doping the RE ions. It is inferred from the profile of partial density of state that RE ions have a strong bonding tendency with F<sup>–</sup> in the crystal. Benefiting from the efficient energy transfer between RE ions and Mn<sup>2+</sup> in KMnF<sub>3</sub>, the green UCL emission is dramatically quenched, and consequently, the GC is endowed with a highly pure red UCL emission. The present study is expected to deepen the understanding of RE ions doping mechanisms in NCs and facilitate the design of highly efficient UCL materials based on nano-glass composites.

Lanthanide doping enabled multimodal luminescence in layered lead-free double perovskite Cs4MnBi2Cl12

Doping lanthanide ions into the Cs4MnBi2Cl12 double perovskite results in multimodal luminescence, and the unique Bi–Mn–Bi sandwich structure facilitates the energy transfer between the transition metal ions and lanthanide ions.

Defect-Interceded Cascading Energy Transfer and Underlying Charge Transfer in Europium-Doped CsPbCl3 Nanocrystals.

Rare-earth ion (RE3+) doping in cesium lead chloride (CsPbCl3) has unlocked novel prospects to explore changes in optical, magnetic, and charge carrier transport properties. This leads to a huge advancement in optoelectronic applications, yet deep understanding of the photophysics governing the energy transfer processes is lacking and demands vital attention. Herein, we probe into the mechanistic transfer processes from the band edge of the host (CsPbCl3) to the dopant europium ion (Eu3+) with the aid of femtosecond fluorescence upconversion and transient absorption (TA) spectroscopy. The upconversion measurement portrays a defect-mediated cascading energy transfer from CsPbCl3 to Eu3+ and further cross-relaxation among Eu3+ states. Moreover, TA studies reveal that there is charge transfer from the band edge of CsPbCl3 to doping-induced shallow defect states. Furthermore, two-photon absorption study establishes no compromise in the transfer mechanism even upon bandgap excitation. This work validates that Eu-CsPbCl3 is an apt entrant for optoelectronic applications.

Polymorph controlled synthesis and photoluminescence properties of Eu3+ doped BiNbO4

Homogeneous doping of rare earth (RE) ions at atomic level is ideal for enhancing luminescence efficiency. Molten-salt synthesis facilitates crystal growth with improved phase-selectivity and dopant homogeneity. Herein, we present a facile and phase-selective synthesis of orthorhombic α-BiNbO4 and monoclinic β-BiNbO4 under Na2SO4-K2SO4 fluxes in the temperature range of 900 °C to 1050 °C. A series of Eu3+ doped BiNbO4 samples with different crystalline structures were obtained. The influences of Eu3+ doping on the crystal structure were systematicly investigated. α-BiNbO4 has a higher Eu3+-doping limit (>15 mol%) while β-BiNbO4 was unstable upon Eu3+ doping and gradually transformed into α-BiNbO4 with the increase of Eu3+ doping concentration. Moreover, all prepared Eu3+ doped BiNbO4 samples can be effectively excited by near-ultraviolet and blue light and exhibit intense red emissions due to the 5D0/7F2 transition of Eu3+ ions. In addition, the quenching concentration can reach above 10 mol% Eu3+ for both polymorphs. The temperature-dependent emission results revealed that α-BiNbO4 possesses a superior thermal stability with activation energy of 0.271 eV, larger than β-BiNbO4 with activation energy of 0.233 eV. The results reported here provide new insights into the understanding of polymorph-dependent property for photon down-conversion rare-earth luminescence of BiNbO4:Eu3+.

Study of magneto-optical properties of GeO2-B2O3-P2O5-ZnO-Tb2O3 glass doped with different rare-earth ions

Paramagnetic magneto-optical glasses doped with different rare-earth ions, 32GeO2–15B2O3–5P2O5–3ZnO-45Tb2O3-RE (RE = 0, 1Ho, 1Pr, 1Er, 1Nd, 1Dy, or 1Ce), referred to as GBPZ-T45-RE magneto-optical glasses, were prepared using a high-temperature melting technique. The effects of rare-earth ion doping on the structure, physical parameters, and magneto-optical properties of these GBPZ-T45-RE glasses and the effects of incident-light wavelength and temperature on the values of the Verdet constants were researched. The refractive indexes and theoretical optical basicities of the glasses were obtained by theoretical calculations. Notably, GBPZ-T45-RE glasses exhibited a large Verdet constant and superior magneto-optical performance; especially, Ho3+ and Pr3+ ions were the most effective in improving the magneto-optical properties. In addition, the Verdet constants were affected by temperature. The Verdet constants of GBPZ-T45-Ho and GBPZ-T45-Pr were determined to be −172.44 and −175.22 rad/(T·m), respectively, under 633 nm light at 298.15 K, values that are significantly greater than that the commercial terbium gallium garnet TGG crystal (−134 rad/(T·m)). The Verdet constants of GBPZ-T45-Ho and GBPZ-T45-Pr under 633 nm light increased to −254.93 and −255.92 rad/(T·m), respectively, at 273.15 K. The excellent magneto-optical properties of these glasses should enable their widespread application in optics, electricity, magnetism, information, communications, military operations, aviation, satellite measurement and control systems, and other fields.

High efficient upconversion luminescence of NaGdF4: Yb3+/Er3+ nanoparticle: first-principles calculation, dual-wavelength stimuli and logic gate application

ABSTRACT First-principle theory was used to design NaGdF4:Yb3+/Er3+ crystal, where the density of state, X-ray diffraction and optical coefficient had been studied through a generalised gradient approximation within density functional theory to predicate the effect of rare earth ion doping on the electronic and optical performance. Besides, NaGdF4:Yb3+/Er3+ nanoparticles were also obtained by liquid–solid–solution method and realized the enhancement of upconversion emission and the regulation of spectrum under co-excitation of the 980 nm and 1550 nm lasers. The results inspired us to establish upconversion logic gate system, where ‘INHIBIT, OR, XOR, YES, AND’ logic gate operations had been successfully developed by introducing external two excitation sources as input signals and monitoring the relative intensity signals of green and red emission bands and G/R ratio signal.

Enhanced strain and electrostrictive properties in lead-free BNT-based ceramics via rare earth doping

Bi0.5Na0.5TiO3 (BNT)-based ceramics are one of the most promising lead-free ferroelectrics due to their high strain property. Compared to other chemical modifications, rare earth ions doping provides significant possibility to optimize the strain property of BNT-based ceramics. In this work, the effects of rare earth ions on phase structure, microstructure, and strain & electrostrictive properties of lead-free BNT-based ceramics were systematically investigated. Rare earth ions (i.e., La3+, Sm3+, Yb3+, Dy3+, and Nd3+) were selected as the doping ions. Introducing moderate La3+ ions can drive the ferroelectric state of BNT-based ceramics to nonergodic relaxor state or ergodic relaxor state. The enhanced strain response of ∼0.40–0.42% and high converse piezoelectric coefficient of ∼600–630 pm/V can be achieved under 60–70 kV/cm for La3+-doped ceramic with nonergodic relaxor state. Besides, the giant electrostrictive coefficient Q33 of ∼0.047 m4/C2 can be obtained for La3+-doped ceramic with ergodic relaxor state. Other rare earth ions also present the promotion effect on strain enhancement for BNT-based ceramics. This study affords a significant guidance to optimize strain and electrostrictive properties of BNT-based ceramics via rare earth ions doping.

Lanthanide-Doped Luminescent Nanophosphors via Ionic Liquids.

Lanthanide (Ln3+) ion(s)-doped or rare-earth ion(s)-doped nanomaterials have been considered a very important class of nanophosphors for various photonic and biophotonic applications. Unlike semiconductors and organic-based luminescent particles, the optical properties of Ln3+-doped nanophosphors are independent of the size of the nanoparticles. However, by varying the crystal phase, morphology, and lattice strain of the host materials along with making core-shell structure, the relaxation dynamics of dopant Ln3+ ions can be effectively tuned. Interestingly, a judicious choice of dopant ions leads to unparallel photophysical dynamics, such as quantum cutting, upconversion, and energy transfer. Recently, ionic liquids (ILs) have drawn tremendous attention in the field of nanomaterials synthesis due to their unique properties like negligible vapor pressure, nonflammability, and, most importantly, tunability; thus, they are often called “green” and “designer” solvents. This review article provides a critical overview of the latest developments in the ILs-assisted synthesis of rare-earth-doped nanomaterials and their subsequent photonic/biophotonic applications, such as energy-efficient lighting and solar cell applications, photodynamic therapy, and in vivo and in vitro bioimaging. This article will emphasize how luminescence dynamics of dopant rare-earth ions can be tuned by changing the basic properties of the host materials like crystal phase, morphology, and lattice strain, which can be eventually tuned by various properties of ILs such as cation/anion combination, alkyl chain length, and viscosity. Last but not least, different aspects of ILs like their ability to act as templating agents, solvents, and reaction partners and sometimes their “three-in-one” use in nanomaterials synthesis are highlighted along with various photoluminescence mechanisms of Ln3+ ion like up- and downconversion (UC and DC).

Highly Enhanced OER Performance by Er-Doped Fe-MOF Nanoarray at Large Current Densities.

Great expectations have been held for the electrochemical splitting of water for producing hydrogen as a significant carbon-neutral technology aimed at solving the global energy crisis and greenhouse gas issues. However, the oxygen evolution reaction (OER) process must be energetically catalyzed over a long period at high output, leading to challenges for efficient and stable processing of electrodes for practical purposes. Here, we first prepared Fe-MOF nanosheet arrays on nickel foam via rare-earth erbium doping (Er0.4 Fe-MOF/NF) and applied them as OER electrocatalysts. The Er0.4 Fe-MOF/NF exhibited wonderful OER performance and could yield a 100 mA cm−2 current density at an overpotential of 248 mV with outstanding long-term electrochemical durability for at least 100 h. At large current densities of 500 and 1000 mA cm−2, overpotentials of only 297 mV and 326 mV were achieved, respectively, revealing its potential in industrial applications. The enhancement was attributed to the synergistic effects of the Fe and Er sites, with Er playing a supporting role in the engineering of the electronic states of the Fe sites to endow them with enhanced OER activity. Such a strategy of engineering the OER activity of Fe-MOF via rare-earth ion doping paves a new avenue to design other MOF catalysts for industrial OER applications.

Effective resistance to dendrite growth of NASICON solid electrolyte with lower electronic conductivity

The interface resistance, relative density and electronic conductivity of ceramic electrolytes show great influences on the formation of dendrites, which is the dominant challenge of solid-state lithium/sodium batteries in the practical application. In this work, NASICON electrolytes (Na3Zr2Si2PO12) with enhanced ionic conductivity, improved relative density and lowered electronic conductivity were demonstrated through doping lanthanide ions (Pr3+, Eu3+ and Lu3+). The influences of lanthanide ions doping on the crystalline structure, density, ionic/electronic conductivity and the application performances especially for the resistance to dendrite growth were investigated in detail. The ionic conductivity and relative density were promoted whereas the electronic conductivity was reduced obviously for the Na3Zr2Si2PO12 electrolyte with the presence of lanthanide ions with low electronegativity, resulting in the promoted resistance to dendrite growth. Among the three types of rare earth ions, highest critical current density (CCD) of 0.9 mA/cm2 at RT was recorded for the Pr3+ doped Na3Zr2Si2PO12 electrolyte due to its compact microstructure and low electronic conductivity, owing to the substitution of Zr4+ ions by the Pr3+ ions with smallest electronegativity and largest ion radius. The presented results proved that the doping of appropriate rare earth ions can significantly decrease the electronic conductivity, resulting in the resistance to sodium dendrite for NASICON solid electrolyte.

Stimuli responsive lanthanide ions doped layered piezophotonic microcrystals for optical multifunctional sensing applications

Multifunctional optical sensing devices are of decisive significance to the miniaturization and integration of optoelectronic devices. However, the development of stimuli responsive materials with multimode emission is still in the early stage, limiting the application of integrated optical sensing. Here, we report the multimode emission piezophotonic material fabricated by doping lanthanide ions into the quaternary piezoelectric semiconductor SrZnOS, achieving multimode emission under various stimulus/excitation sources (ultraviolet, near-infrared laser, X-ray, and force), due to its multifunctional optical properties. Particularly the mechanoluminescence has been realized covering both the visible and near-infrared spectral bands. Optical stress sensing was achieved by establishing a quantitative relationship between force and light conversion. Moreover, near-infrared mechanoluminescence can effectively resist the interference of ambient light. The temperature detection performance and the power-dependent color tunability of the sample were also evaluated for multifunctional applications. All the results indicate that the developed multifunctional optical materials with inherent multimode light-emitting characteristics have the potential in advanced optical sensing and anti-counterfeiting applications. The piezophotonic material with multimode emission has been developed by doping lanthanide ions into layered quaternary piezoelectric semiconductor SrZnOS. The materials can be responsive to external stimuli (X-ray, UV light, NIR laser, stress), which could be used for energy conversion and optical stress/temperature dual-sensing. • Lanthanide ions doped SrZnOS is synthesized for stress/temperature dual-sensing. • It can be responsive to multi-mode stimuli (X-ray, UV light, NIR laser, stress). • The material can generate mechanoluminescence covering visible and NIR region. • The developed flexible composite can be used for energy conversion and sensing.

Optimized strain properties with small hysteresis in BNT-based ceramics with ergodic relaxor state

Electric field-induced high strain with small hysteresis and good temperature stability is necessary for piezoactuators devices. Most of previous works focus on the giant strain achieved in Bi0.5Na0.5TiO3 (BNT)-based ceramics through electric field-induced transition from nonergodic relaxor to ferroelectric state, while the high remnant strain or/and large hysteresis are always accompanying. In this work, through enhancing the local polarization by rare earth ions doping (e.g., La3+), we propose to improve the strain properties of BNT-based lead-free ceramics with ergodic relaxor state which displays the near zero remnant strain, small hysteresis, high temperature stability but the low strain value. The addition of La3+ would not change the ergodic relaxor state, but can improve the short-range correlation of local polar nanoregions, cut down the critical electric field of transition between relaxor and ferroelectric states, and elevate the electrostrictive effect of ceramics. Finally, high strain of ∼0.3 % with low hysteresis of ∼8−30 % was obtained in the broad temperature range from room temperature to 100 °C, which is superior to previous BNT-based ceramics and other lead-based/lead-free ceramics. This work affords a paradigm to regulate the ergodic relaxor state to optimize the strain properties, which give the significant guide for strain developments.

Ancilla-mediated qubit readout and heralded entanglement between rare-earth dopant ions in crystals

Owing to their long excited state lifetimes, rare-earth ions in crystals are widely used in quantum applications. To allow optical readout of the qubit state of individual ions, we propose to dope the crystal with an additional nearby ancilla ion with a shorter radiative lifetime. We show how a Bayesian analysis exhausts the information about the state of the qubit from the optical signal of the ancilla ion. We study the effects of incoherent processes and propose ways to reduce their effect on the readout. Finally, we extend the architecture to ions residing in two remote cavities, and we show how continuous monitoring of fluorescence signals from the two ancilla ions leads to entanglement of the qubit ions.

Effective enhancement on mid-infrared fluorescence emission of Ho3+/Yb3+ doped tellurite glass introduced Ag nanoparticles

Abstract In this paper, Ho3+, Yb3+ and metal Ag nanoparticles (NPs) tri-doped tellurite glass were synthesized by melt quenching. Combining X-ray diffraction, Raman spectroscopy, and Differential thermal analysis tests, multiple structural units were found in the synthetic glass samples which provided the possibility to achieve high concentration and uniform doping of rare earth ions without degrading the glass forming ability and thermal stability. The fluorescence emission of glasses at 2 μm, 3.9 μm, and 4.1 μm were focused on, as a consequence, the Ho3+/Yb3+/AgNPs tri-doped tellurite glass achieved strong emission at 2 μm, 3.9 μm and 4.1 μm, and the full width at half maximum (FWHM) at 4.1 μm is 316 nm under the 980 nm LD excitation, which realized broadband fluorescence emission. In addition, the fluorescence lifetimes of the glass at 2 μm, 3.9 μm and 4.1 μm are 4.79 ms, 3.81 ms and 4.28 ms meaning the lower laser oscillation threshold the glass holds. It is particularly noteworthy that the emission intensity had been greatly improved about 30% at 2 μm and 27% at 3.9 μm and 4.1 μm with the introduction of AgCl into the matrix, respectively, which was mainly effected by local surface plasmon resonance (LSPR) of AgNPs and the energy transfer between Ag species and Ho3+, whereas the content of AgCl must be strictly controlled to prevent the concentration quenching to decrease the emission intensity. The obtained results demonstrate that Ho3+/Yb3+/AgNPs tri-doped tellurite glass possesses an ideal application prospect on mid-infrared fiber and laser materials.

Sensitizing Full‐Spectrum Lanthanide Luminescence within a Semiconductor CaZnOS Host

Lanthanide Luminescence The cover image shows a crystal structure of CaZnOS that permits doping of various lanthanide ions due to the Ca2+ sites in the host lattice. In article number 2000089, Feng Wang and co-workers show that, upon photoexcitation into the host lattice, efficient energy transfer to the lanthanide dopant ions occurs and results in tunable optical emissions spanning the visible and near-infrared spectrum.

Hexagonal Sodium Lutetium Fluoride Microstructures: Facile and Large-Scale Synthesis, Growth Mechanism and Multicolour Emissions

Highly crystalline β-NaLuF4:Ln3+ microstructures were successfully prepared via a mixed NaCl-KCl flux cooling approach. The chemical reaction process and the formation mechanism have been carefully investigated by XRD, SEM, TEM and PL characterizations. Interestingly, as the reaction time is prolonged, the crystalline structure of NaLuF4 changes from α-phase to β-phase, while the granule shape transfers from nanoparticles to solid microsheets then to porous microsheets. By altering the kinds of doped lanthanide ions, upconverting and downconverting luminescence with multi-colour outputs (red, green and blue) can be realized in β-NaLuF4:Ln3+ (Ln = Yb, Er, Tm, Ce, Tb and Eu). This strategy is not only expected to meet the ever-increasing commercial demand, but also offers an alternative in synthesizing rare earth fluorides.

Optical tweezers beyond refractive index mismatch using highly doped upconversion nanoparticles.

Optical tweezers are widely used in materials assembly1, characterization2, biomechanical force sensing3,4 and the in vivo manipulation of cells5 and organs6. The trapping force has primarily been generated through the refractive index mismatch between a trapped object and its surrounding medium. This poses a fundamental challenge for the optical trapping of low-refractive-index nanoscale objects, including nanoparticles and intracellular organelles. Here, we report a technology that employs a resonance effect to enhance the permittivity and polarizability of nanocrystals, leading to enhanced optical trapping forces by orders of magnitude. This effectively bypasses the requirement of refractive index mismatch at the nanoscale. We show that under resonance conditions, highly doping lanthanide ions in NaYF4 nanocrystals makes the real part of the Clausius-Mossotti factor approach its asymptotic limit, thereby achieving a maximum optical trap stiffness of 0.086 pN μm-1 mW-1 for 23.3-nm-radius low-refractive-index (1.46) nanoparticles, that is, more than 30 times stronger than the reported value for gold nanoparticles of the same size. Our results suggest a new potential of lanthanide doping for the optical control of the refractive index of nanomaterials, developing the optical force tag for the intracellular manipulation of organelles and integrating optical tweezers with temperature sensing and laser cooling7 capabilities.

Upconversion properties in lanthanide doped layered-perovskite, CsBiNb2O7

Despite advances of lanthanide-doped upconversion (UC) materials, the applications such as light-emitting diode and biological imaging are limited by low quantum efficiency. For this context, the understanding of unique interactions between the doped-lanthanides and the host crystals has attracted a huge amount of the researcher's interest. In particular, it was revealed that doping lanthanide ions in a non-centrosymmetric site of host lattice is the cause of relaxation of the Laporte selection rule in the 4f-4f transition of lanthanide ions. One of the layered perovskites CsBiNb2O7 is known to have non-centrosymmetric sites, which would lead to highly bright UC emission. Nevertheless, to our knowledge, there has been no research on the UC comparison between host materials of CsBiNb2O7 with other hosts. In this article, we present the UC intensity comparison of Yb3+-Er3+ ion doped CsBiNb2O7, NaYF4, BaTiO3, and SrTiO3 hosts (the UC in CsBiNb2O7:Er3+,Yb3+ was 2.4 times that of NaYF4:Er3+,Yb3+ and ∼70 times that of SrTiO3:Er3+,Yb3+). After that, we dig into UC, downshifting, and double beam system UC properties. The activator concentration was optimized by varying the doping ratio of Yb3+ and Er3+, and we found out the main reason for the concentration quenching behavior in Er3+ ion doped CsBiNb2O7 is dipole-dipole interaction. In addition, the double excitation experiment indicates that the absorption (4I15/2 → 4I13/2) factor is stronger than the stimulated emission (4I13/2 → 4I15/2) factor in CsBiNb2O7 under 1540 nm laser irradiation.

Pourbaix-Guided Mineralization and Site-Selective Photoluminescence Properties of Rare Earth Substituted B-Type Carbonated Hydroxyapatite Nanocrystals

Rare-earth labeling in biological apatite could provide critical information for the pathologic transition (osteoclastic) and physiologic regeneration (osteogenesis) of bone and teeth because of their characteristic site-sensitive fluorescence in different coordinative conditions of various tissues in many biological processes. However, the rare-earth labeling method for biological apatites, i.e., carbonated-hydroxyapatite, has been rarely found in the literature. In this paper, we report a Pourbaix-diagram guided mineralizing strategy to controllable carbonation and doping of rare-earth ions in the hydroxyapatite (HA) lattice. The carbonation process of hydroxyapatite was achieved by controllable mineralization in hydrothermal condition with K2CO3 as the carbonate source, which results into the pure B-type carbonated hydroxyapatite (CHA) with tunable carbonate substitution degree. All of the as-synthesized materials crystalized into P63/m (No. 176) space group with the lattice parameter of a decreases and c increases with the increasing of carbonate content in the reactants. Structural refinement results revealed that the substitution of planar CO32− is superimposed on one of the faces of PO43− tetrahedral sub-units with a rotation angle of 30° in reference to c-axis. All of the hydrothermally synthesized CHA nanocrystals show hexagonal rod-like morphology with the length of 70–110 nm and diameter of 21–35 nm, and the decreasing length/diameter ratio from 3.61 to 2.96 from low to high carbonated level of the samples. Five rare-earth cations, of Pr3+, Sm3+, Eu3+, Tb3+, and Ho3+, were used as possible probe ions that can be doped into either HA or CHA lattice. The site-preference of Tb3+ doping is the same in the crystallographic site of HA and CHA according to characteristic emission peaks of 5D4–7Fj (j = 3–6) transitions in their photoluminescent spectroscopy. Our work provides a controllable carbonation method for rare-earth labeling hydroxyapatite nanomaterials with potential biologically active implant powders for bone repair and tissue regeneration.