Disappearance and Recovery of Luminescence in Bi3+, Eu3+ Codoped YPO4 Nanoparticles Due to the Presence of Water Molecules Up to 800 °C

Bismuth and Vanadium-Substituted Yttrium Phosphates for Cool Coating Applications

Luminescent yttrium phosphate is engineered into an environmentally benign near infrared (NIR) reflective yellow pigment by the substitution of bismuth and vanadium metals in the host lattice. A series of YP_(1-x)V _x O₄ (x = 0, 0.05, 0.1, 0.15, 0.2, and 0.4), Y_(1-y)Bi _y PO₄ (y = 0.1 and 0.3), and Y_(1-y)Bi _y P_(1-x)V _x O₄ (x = y = 0.2, 0.4, and 0.6) were prepared by the precipitation method. Secondary phase was noticed at x = 0.2 and y = 0.2 while substituting vanadium and bismuth, respectively, due to high ionic radii of the dopant ions. Co substitution of vanadium and bismuth in the YPO₄ lattice enhanced both NIR reflectance and yellow color of all the fabricated materials. XPS spectra proved the presence of trivalent bismuth and pentavalent vanadium in Y_0.4Bi_0.6P_0.4V_0.6O₄. Due to the substitution effect, a more defined morphology was noticed, which enhanced the scattering co-efficient of the fabricated materials; hence, the NIR reflectance of the materials was increased from 68% (YPO₄) to 83% (Y_0.4Bi_0.6P_0.4V_0.6O₄). Chemical and thermal stability test of Y_0.4Bi_0.6P_0.4V_0.6O₄ confirmed the color and strength of the designed pigment. With good yellow hue (b* = +56.06), high NIR solar reflectance (R* = 83%), and good stability, Y_0.4Bi_0.6P_0.4V_0.6O₄ can act as an environmentally benign cool yellow pigment.

Deterministic Relation between Optical Polarization and Lattice Symmetry Revealed in Ion-Doped Single Microcrystals

Rare-earth ion doped crystals are of great significance for microsensing and quantum information, while the ions in the crystals emit light with spontaneous partial polarization, which is, though believed to be originated from the crystal lattice structure, still lacking a deterministic explanation that can be tested with quantitative accuracy. We report experimental evidence showing the profound physical relation between the polarization degree of light emitted by the doped ion and the lattice symmetry by demonstrating, with high precision, that the lattice constant ratio c/a directly quantifies the macroscopic effective polar angle of the electric and magnetic dipoles, which essentially determines the linear polarization degree of the emission. Based on this result, we further propose a pure optical technology to identify the three-dimensional orientation of a rod-shaped single microcrystal using the polarization-resolved microspectroscopy. Our results, demonstrating the physical origin of light polarization in ion-doped crystals, allow work toward on-demand polarization control with crystallography and provide a versatile platform for polarization-based microscale sensing in dynamical systems.

Deciphering the role of temperature in Li+ co-dopant occupancy in BaYF5:Yb3+,Er3+ up-converting nanocrystals and its structure-property relationship

Precision engineering of defects in luminescent nanoscale crystalline materials with lesser controls to design is an area of interest in engineering materials with desired properties. Li⁺ co-doped BaYF₅ nanocrystals were engineered, and temperature as controls for determining the co-dopant occupancies in the host lattice is studied. An observed enhancement in the up-conversion photoluminescence results from the co-dopant occupancy at Ba²⁺ sites via substitution through the hot injection method, whereas for samples prepared using co-precipitation, photoluminescence quenching was observed, which can be correlated with the Li⁺ occupancy at the interstitial site near Er³⁺ and also due to the incorporation of OH^-. The crystal lattice deformation as a result of doping and the mechanism for the observed enhancement/quenching of luminescence are studied using x-ray diffraction, x-ray photoelectron spectroscopy, and energy transfer mechanism. Cytotoxicity assay and photoluminescence studies of the synthesized nanocrystals confirm that the material is biocompatible.

Super Bright Red Upconversion in NaErF4:0.5%Tm@NaYF4:20%Yb Nanoparticles for Anti-counterfeit and Bioimaging Applications

Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600-900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF₄:0.5%Tm@NaYF₄:20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF₄:0.5%Tm@NaYF₄ (core@inactive shell). Here, an Er³⁺-enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er³⁺ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm³⁺ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb³⁺ ions efficiently transfers the energy to the Er³⁺-enriched core, which suppresses the nonradiative channel rate, and Tm³⁺ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.

Tuning the Langasite, La3SbZn3Si2O14, towards white light emission: synthesis, structure, SHG and photoluminescence studies

A series of single-phase color-tunable Langasite, La3SbZn3Si2O14:RE3+ (RE = Eu, Tb, and Tm) phosphors have been prepared and characterized employing X-ray diffraction (XRD), Raman, and photoluminescence (PL) studies. The substituted compounds, La3SbZn3Si2O14:Eu3+, La3SbZn3Si2O14:Tb3+ and La3SbZn3Si2O14:Tm3+ exhibit the characteristic emissions of Eu3+ (red), Tb3+ (green) and Tm3+ (blue), respectively. By carefully adjusting the concentration of Eu3+ ions in the La3SbZn3Si2O14:1% Tm3+, 2% Tb3+, x% Eu3+ system, we achieved a white emission with a reasonable quantum yield. The compounds are found to be SHG (second-harmonic generation) active with the highest values of 3.6 × KDP (potassium dihydrogen phosphate). In addition, the compounds exhibit reasonable dielectric constants with low loss. The present study demonstrates the color tunability of the Langasite family of compounds and establishes it as an adaptable structure.

HDEHP assisted solvothermal synthesis of monodispersed REPO4 (RE = La–Lu, Y) nanocrystals and their photoluminescence properties

In this paper, a novel method is reported for the preparation of spherical REPO₄ particles.

GdPO4-Based Nanoprobe for Bioimaging and Selective Recognition of Dipicolinic Acid and Cysteine by a Sensing Ensemble Approach

Multiple functions incorporated in one single-component nanoplatform pave the way for important biomedicine applications. Herein, a multifunctional terbium-doped gadolinium orthophosphate (GdPO₄:Tb-EDTA) nanoplatform was prepared through a simple, ecofriendly, one-step hydrothermal method. Results showed that dipicolinic acid (DPA), the biomarker of bacterial spores, significantly increased the fluorescence intensity of this nanoplatform and conferred it with rapid response and excellent selectivity. Subsequently, the fluorescence of the ensemble GdPO₄:Tb-EDTA-DPA can be remarkably quenched by Cu²⁺, which led to a rewritable nanosensor used in the detection of cysteine (Cys) with excellent sensitivity. In addition, GdPO₄:Tb-EDTA can also be a potential T₁-weighted magnetic resonance imaging (MRI) contrast agent, which indicated a satisfactory in vitro MRI with r₁ relaxivity values of 13.9 mM^-1 s^-1 and in vivo MRI through intravenous administration on a rat model. Overall, the proposed assay may have great theoretical and practical significance for designing multifunctional biomaterials.

Double cascade dressed MOSFET from doped Eu3+and Pr3+ in a host YPO4

In this paper, we study double cascade dressed optical metal oxide semiconductor field-effect transistor (MOSFET) by exploiting enhancement and suppression for mixed-phase (hexagonal + tetragonal) of Eu³⁺:YPO₄ and different phases (hexagonal + tetragonal and pure tetragonal) of Pr³⁺:YPO₄ crystals. We report variation of fine structure energy levels in different doped ions (Eu³⁺ and Pr³⁺) in the host YPO crystal. We compared multi-level energy transition from a single dressing laser with single level energy transition from double cascade dressing lasers. Gate delay facilitates multi-energy level dressed transition and is modeled through a Hamiltonian. Based on the results of double cascade dressing, we have realized MOSFET for logic gates (inverter and logic not and gate) with a switching contrast of about 92% using a mixed phase of Pr³⁺:YPO₄.

By changing different parameters of single and double lasers, we observed the dressed energy level transition from single to multi-level with a single laser. Each sample responded based on their ions' structure and phase symmetry in the host YPO crystal.

Photonic structuring improves the colour purity of rare-earth nanophosphors

Nanophosphor integration in an optical cavity allows unprecedented control over both the chromaticity and the directionality of the emitted light, without modifying the chemical composition of the emitters or compromising their efficiency. Our approach opens a route towards the development of nanoscale photonics based solid state lighting.

Charge compensation assisted enhancement of photoluminescence in combustion derived Li+ co-doped cubic ZrO2:Eu3+ nanophosphors

Red light emitting cubic Zr_0.99Eu_0.01O₂:Li⁺ (0-9 mol%) nanoparticles are synthesized by a low temperature, self-propagating solution combustion method using oxalyl di-hydrazide (ODH) as fuel. In this study, we report systematic investigation of the effect of lithium ion (Li⁺) concentration on the structural properties and the photoluminescence of zirconia. With increasing lithium concentration, the crystallinity of the samples increases and the lattice strain decreases. The higher crystallinity is likely due to charge compensation achieved by replacing one Zr⁴⁺ ion by a Eu³⁺ and a Li⁺ ion. Scanning electron micrographs (SEM) reveal a mesoporous structure characteristic of combustion derived nanomaterials. Photoluminescence (PL) spectra show that the intensity of the red emission (606 nm) is highly dependent on Li⁺ ion concentration. Furthermore there is a promising enhancement in the associated lifetime. Upon Li⁺ doping, the PL intensity of the samples is found to increase by two fold compared to the undoped sample. Variation of PL intensity with Li⁺ concentration is attributed to the differences in probability of non-radiative recombination (relaxing). Intensity parameters (Ω₂, Ω) and radiative properties such as transition rates (A), branching ratios (β), stimulated emission cross-section (σ_e), gain bandwidth (σ_e × Δλ_eff) and optical gain (σ_e × τ) are calculated using the Judd-Ofelt theory. The calculated values suggest that in optimally co-doped samples, in addition to improved crystallinity and charge compensation, the lowering of Eu³⁺ site symmetry and the increase in the covalency of Eu-O bonding due to interstitial Li are responsible for the observed enhancement in PL intensity.

Adsorption of arsenic, phosphorus and chromium by bismuth impregnated biochar: Adsorption mechanism and depleted adsorbent utilization

Bismuth impregnated biochar were synthesized to deal with wastewater pollution. Nitrogen adsorption-desorption isotherms, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to determine the characteristics of adsorbents and explore the main adsorption mechanism. Results showed that bismuth particle was carried successfully within the biochar matrix, making contributions to creating micropore and boost specific surface area. The loaded bismuth, served as the adsorption site, rather than the specific surface area played an important role in arsenic and phosphorus adsorption. Batch adsorption experiments demonstrated a fit Langmuir model for arsenic (As) and phosphorus (P) and a suitable Freundlich model for chromium (Cr). Thermodynamic parameters depicted the endothermic nature and the spontaneous process for phosphate and arsenic adsorption. Besides, this contaminant-loaded carbon adsorbent was further applied for the removal of methylene blue from aqueous solution.

Bismuth Complexes in Phenylazomethine Dendrimers: Controllable Luminescence and Emission in the Solid State

Dendritic phosphors were obtained by the stepwise integration of BiCl₃ in phenylazomethine dendrimers. The bismuth-coordinated phenylazomethines displayed photoluminescence at 500-800 nm, and the intensity could be tuned by changing the stoichiometry of BiCl₃ and the dendrimer. This phosphor did not show serious luminescence quenching even though the local concentration of BiCl₃ in the dendrimer was as high as 20 M, and luminescence was also observed in the solid state. The absorption and emission properties could be reversibly switched by addition of a Lewis base or under electrochemical redox control, which induced the reversible complexation of BiCl₃ in the dendrimer.

Future prospects of luminescent nanomaterial based security inks: from synthesis to anti-counterfeiting applications

Counterfeiting of valuable documents, currency and branded products is a challenging problem that has serious economic, security and health ramifications for governments, businesses and consumers all over the world. It is estimated that counterfeiting represents a multi-billion dollar underground economy with counterfeit products being produced on a large scale every year. Counterfeiting is an increasingly high-tech crime and calls for high-tech solutions to prevent and deter the acts of counterfeiting. The present review briefly outlines and addresses the key challenges in this area, including the above mentioned concerns for anti-counterfeiting applications. This article describes a unique combination of all possible kinds of security ink formulations based on lanthanide doped luminescent nanomaterials, quantum dots (semiconductor and carbon based), metal organic frameworks as well as plasmonic nanomaterials for their possible use in anti-counterfeiting applications. Moreover, in this review, we have briefly discussed and described the historical background of luminescent nanomaterials, basic concepts and detailed synthesis methods along with their characterization. Furthermore, we have also discussed the methods adopted for the fabrication and design of luminescent security inks, various security printing techniques and their anti-counterfeiting applications.

Facile hydrothermal synthesis and multicolor-tunable luminescence of YPO4:Ln3+ (Ln = Eu, Tb)

This work investigates a novel facile hydrothermal conversion method for the synthesis of uniform cuboid YPO₄ and obtains multicolor emissions in YPO₄:Tb³⁺, Eu³⁺ samples, and the energy transfer efficiency reachs about 94.30%.

Terbium doped SnO2 nanoparticles as white emitters and SnO2:5Tb/Fe3O4 magnetic luminescent nanohybrids for hyperthermia application and biocompatibility with HeLa cancer cells

SnO2:5Tb (SnO2 doped with 5 at% Tb(3+)) nanoparticles were synthesised by a polyol method and their luminescence properties at different annealing temperatures were studied. Characterization of nanomaterials was done by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and vibrating sample magnetometry (VSM). XRD studies indicate that the prepared nanoparticles were of tetragonal structures. Upon Tb(3+) ion incorporation into SnO2, Sn(4+) changes to Sn(2+) and, on annealing again at higher temperature, Sn(2+) changes to Sn(4+). The prepared nanoparticles were spherical in shape. Sn-O vibrations were found from the FTIR studies. In photoluminescence studies, the intensity of the emission peaks of Tb(3+) ions increases with the increase of annealing temperature, and emission spectra lie in the region of white emission in the CIE diagram. CCT calculations show that the SnO2:5Tb emission lies in cold white emission. Quantum yields up to 38% can be obtained for 900 °C annealed samples. SnO2:5Tb nanoparticles were well incorporated into the PVA polymer and such a material incorporated into the polymer can be used for display devices. The SnO2:5Tb/Fe3O4 nanohybrid was prepared and investigated for hyperthermia applications at different concentrations of the nanohybrid. This achieves a hyperthermia temperature (42 °C) under an AC magnetic field. The hybrid nanomaterial SnO2:5Tb/Fe3O4 was found to exhibit biocompatibility with HeLa cells (human cervical cancer cells) at concentrations up to 74% for 100 μg L(-1). Also, this nanohybrid shows green emission and thus it will be helpful in tracing magnetic nanoparticles through optical imaging in vivo and in vitro application.

Roles of solvent, annealing and Bi3+ co-doping on the crystal structure and luminescence properties of YPO4:Eu3+ nanoparticles

There are roles of solvent, annealing and Bi³⁺ co-doping on crystal structure and luminescence properties of YPO₄:Eu³⁺ nanoparticles.

p-Aminobenzoic acid (pABA) sensitization of LaF3:Tb3+ nanoparticles and its applications in the detection of explosive materials

“A novel approach for detecting highly explosive aromatic nitro compounds utilizing pABA sensitised terbium (Tb³⁺) doped spherical LaF₃ nanoparticles.”

C-dot sensitized Eu3+ luminescence from Eu3+-doped LaF3–C dot nanocomposites

C-dot sensitized strong Eu³⁺ luminescence is observed in Eu³⁺-doped LaF₃–C-dot nanocomposites via energy transfer.

Facile preparation and bifunctional imaging of Eu-doped GdPO4 nanorods with MRI and cellular luminescence

Eu-doped GdPO₄ NRs coated by silk fibroin have been prepared in a template of silk fibroin (SF) peptides via a mineralization process. A growth mechanism of SF-NRs is proposed to explain their stronger luminescence, better cyto-compatibility and higher longitudinal relaxivity r₁.

Improved photo-luminescence behaviour of Eu3+ activated CaMoO4 nanoparticles via Zn2+ incorporation

Zn²⁺ (0, 2, 5, 7 and 10 at%) co-doped CaMoO₄:2Eu³⁺ nanophosphors have been synthesized via the polyol method using ethylene glycol (EG) as both capping agent and reaction medium at 150 °C.

One-pot synthesis of 2-thenoyltrifluoroacetone surface functionalised SrF2:Eu3+ nanoparticles: trace level detection of water

Trace level detection of water by 2-thenoyltrifluoroacetone Surface functionalised fluorescent lanthanide (Eu³⁺) doped SrF₂ nanoparticles.

Microwave synthesis, photoluminescence, and photocatalytic activity of PVA-functionalized Eu3+-doped BiOX (X = Cl, Br, I) nanoflakes

We report a facile microwave-assisted green synthetic route for colloidal poly(vinyl alcohol) (PVA)-coated europium (Eu(3+))-doped luminescent heavy metal bismuth oxyhalide (BiOX; X = Cl, Br, I) nanoflakes at low temperature and examine their structural, optical, and photocatalytic characteristics. PVA coating onto the surface of the nanoflakes endows them with hydrophilic nature. Both Eu(3+)-doped BiOCl and BiOBr nanoflakes exhibit strong optical properties related to Eu(3+) and Bi(3+) which are quenched in case of Eu(3+)-doped BiOI matrix. These results are supported by Eu(3+) photoluminescence lifetime values of 0.61 ms, 0.59 ms, and 8.9 μs, respectively. The former two matrices have quite similar crystal field environments as deduced from the asymmetric ratios of (5)D0 → (7)F2 (614 nm) and (5)D0 → (7)F1 (591 nm) transitions. In addition to possessing interesting photoluminescence properties, a comparison of the photocatalytic activity of Eu(3+)-doped BiOX (X = Cl, Br, I) nanoflakes, with corresponding estimated band gaps of 3.36, 2.74, and 1.67 eV has been evaluated using Rhodamine B (RhB) dye under visible light irradiation. The nanoflakes exhibited 100% dye degradation under visible light irradiation. Eu(3+)-doped BiOCl nanoflakes manifested higher photocatalytic efficiency compared to the other matrices following apparent first-order kinetics. Such a boost in efficiency is attributed to their high surface area to volume ratios, layered crystalline structures, indirect band gap nature, and ability to utilize broad bands in the solar spectrum.

Near-infrared photocatalysts of BiVO₄/CaF₂:Er³⁺, Tm³⁺, Yb³⁺ with enhanced upconversion properties

Upconversion photocatalysts have the potential to absorb the near-infrared (NIR) light in solar energy and improve the photocatalytic performance. A hierarchical upconversion photocatalyst of BiVO₄ (BVO)/CaF₂:Er(3+), Tm(3+), Yb(3+) (CF) combined with the narrow-band semiconductor of BVO and the luminescence agent of CF to enhance upconversion properties was synthesized via the hydrothermal method. The CF particles were deposited homogeneously on the surface of the BVO/CF composite with regular dendritic structure, which led to efficient upconversion emissions. The upconversion emission intensity of the BVO/CF composite was 8 times higher than that of pure CF, through tailoring the crystal symmetry of lanthanide ions by Bi(3+) ions. The upconverted ultraviolet (361 and 379 nm), violet (408 nm), and blue (485 nm) light was able to excite BVO for photocatalysis in BVO/CF under NIR irradiation, which improved the degradation rate of methyl orange (MO).

Energy transfer from Bi3+ to Ho3+ triggers brilliant single green light emission in LaNbTiO6:Ho3+, Bi3+ phosphors

LaNbTiO₆:Ho³⁺, Bi³⁺ was synthesized and the remarkably enhance of photoluminescence intensity was ascribed to efficient energy transfer from Bi³⁺ to Ho³⁺.

Morphology and dopant-dependent optical characteristics of novel composite 1D and 3D-based heterostructures of CdSe nanocrystals and LaPO4:Re (Re = Eu, Ce, Tb) metal phosphate nanowires

Observation of morphology and dopant dependent optical behavior in novel quantum dot-metal oxide-based heterostructures.

Is BiPO4 a better luminescent host? Case study on doping and annealing effects

Metal phosphates have been popularly regarded as excellent luminescence hosts of lanthanide ions, while such an issue is challenged by the ignorance about the structural stability that may originate from the different chemical nature between the framework and the dopant lanthanide ions. Here, we choose BiPO(4) as a model compound to study. A detailed investigation of the effects of Eu doping and annealing on the structures and related luminescence properties of Bi(1-x)PO(4):Eu(x) (x = 0-0.199) has been carried out. A monoclinic phase (denoted as LTMP) was obtained for the undoped sample, which gradually transformed to a hexagonal phase (HP) with increasing doping level of Eu(3+) to x = 0.068. Further, it is also found that annealing had an obvious impact on the structures of the resulted samples. With increasing the annealing temperature up to 400 °C a phase transformation from HP to LTMP happens, which is opposite to that with doping. The above phase transformation behaviors were further confirmed by performing structural studies of doping with Dy(3+) ions and annealing undoped BiPO(4). The structural evolution had a great influence on the luminescent properties. Initially a significant decrease in Eu(3+) luminescence intensity and quantum efficiency was observed when LTMP transformed to HP. Afterward, a converse situation, increasingly enhanced luminescence performance, appeared when HP transformed to LTMP. Therefore, whether metal phosphates could be taken as better luminescence hosts must take into account their structural changes caused by the different chemical natures between framework and dopant ions, which may provide an important reference for designing new luminescent materials.

Optical properties of Eu³+ ions in phosphate glasses

Eu(3+)-doped phosphate (P(2)O(5)+K(2)O+SrO+Al(2)O(3)+Eu(2)O(3)) glasses with varying Eu(2)O(3) concentration have been prepared by standard melt quenching technique and are characterized through various spectroscopic techniques at room temperature. Luminescence spectra of these glasses exhibit the characteristic emission of Eu(3+) ion with an intense and most prominent red emission attributed to (5)D(0)→(7)F(2) transition. Crystal-field analysis has been carried out to estimate the local symmetry in the vicinity of Eu(3+) ions. Judd-Ofelt parameters have been evaluated from the luminescence intensity ratios of (5)D(0)→(7)F(J) (J=2, 4 and 6) to (5)D(0)→(7)F(1) transitions as well as absorption spectrum under different constraints. Decay rates for the (5)D(0) level of Eu(3+) ions have been recorded by monitoring the emission at around 609 nm corresponding to (5)D(0)→(7)F(2) transition. The experimental lifetime for the (5)D(0) level in title glasses is independent of Eu(3+) ion concentration.