Modifying phase, shape and optical thermometry of NaGdF4:2%Er3+ phosphors through Ca2+ doping

Narrow-band dazzling red-emitting (LiCaLa(MoO4)3:Eu3+) phosphor with scheelite structure for hybrid white LEDs and LiCaLa(MoO4)3:Sm3+,Eu3+-based deep-red LEDs for plant growth applications

Presently, the preparation of dazzling narrow-band red-emitting phosphors for solid-state lighting is still a challenge. In this context, herein, a series of pure narrow-band red-emitting LiCaLa1-xEux(MoO4)3 phosphors was synthesized and characterized, and their spectroscopic properties were systematically studied. In addition, a series of orange-red-emitting LiCaLa1-ySmy(MoO4)3 phosphors with the simultaneous doping of Eu3+ was synthesized for plant growth applications. The optical studies revealed that the phosphors showed pure red emission with a full width at half maximum of ∼5 nm and 97% color purity. Alternatively, their absorption spectrum showed good absorption strength in the near UV to blue region. Non-concentration quenching behavior was observed even when the concentration of Eu3+ in the lattice was 100%. The dominant electric dipole transition in the emission spectrum indicated that the Eu3+ ion occupies a non-centrosymmetric site in the lattice. At 150 °C, the phosphor retained 88.83% of its emission intensity calculated at room temperature. Thus, it can be useful for the fabrication of LEDs. Subsequently, Eu-rich red and white LEDs (integrated with yellow phosphor) were fabricated with near-UV and blue LED chips, respectively. The fabricated hybrid white LED showed pure white emission with a CCT of 4762 K, CRI of 81%, and close CIE coordinates of (0.34, 0.33). The absolute quantum yield for the fully substituted LiCaEu(MoO4)3 composition was calculated to be 44.50% upon excitation at 395 nm. To utilize LED light for plant growth applications, efforts were made to synthesize orange-red (Sm3+) and deep-red (Sm3+, Eu3+) phosphors and utilize the simultaneously doped phosphor for the fabrication of deep-red LEDs. The spectral lines well-matched the spectrum of phytochrome (Pr). Thus, the phosphor in the present study is a potential candidate as a red and deep-red phosphor for the fabrication of hybrid white LEDs and deep-red LEDs (for plant growth purposes), respectively.

Synthesis and Crystal Structure of the Europium(II) Hydride Oxide Iodide Eu5H2O2I4 Showing Blue-Green Luminescence

As the first europium(II) hydride oxide iodide, dark red single crystals of Eu5H2O2I4 could be synthesized from oxygen-contaminated mixtures of EuH2 and EuI2. Its orthorhombic crystal structure (a = 1636.97(9) pm, b = 1369.54(8) pm, c = 604.36(4) pm, Z = 4) was determined via single-crystal X-ray diffraction in the space group Cmcm. Anion-centred tetrahedra [HEu4]7+ and [OEu4]6+ serve as central building blocks interconnected via common edges to infinite ribbons parallel to the c axis. These ribbons consist of four trans-edge connected (Eu2+)4 tetrahedra as repetition unit, two H--centred ones in the inner part, and two O2--centred ones representing the outer sides. They are positively charged, according to ∞1{[Eu5H2O2]4+}, to become interconnected and charge-balanced by iodide anions. Upon excitation with UV light, the compound shows blue-green luminescence with the shortest Eu2+ emission wavelength ever observed for a hydride derivative, peaking at 463 nm. The magnetic susceptibility of Eu5H2O2I4 follows the Curie-Weiss law down to 100 K, and exhibits a ferromagnetic ordering transition at about 10 K.

Effect of Sr2+ ions on the structure, up-conversion emission and thermal sensing of Er3+, Yb3+ co-doped double perovskite Ba(2-x)SrxMgWO6 phosphors

Investigating the effect of different phases on the optical performance is crucial for thermal sensing phosphor materials. Ba_(2-x)Sr_xMgWO₆:Er³⁺, Yb³⁺, K⁺ double perovskite phosphors were successfully prepared using a high-temperature solid-phase method. The dominant up-conversion luminescent (UCL) mechanism was deduced by analyzing the power-dependence spectra and energy level diagrams. By X-ray diffraction tests and tolerance factor calculations, it was demonstrated that the substitution of Sr²⁺ ions for Ba²⁺ ions led to the phase changing from cubic to tetragonal. The phase transition led to a decrease in the crystallographic symmetry of the compounds and changes in the optical thermometric properties. The optical temperature sensing properties were investigated using the fluorescence intensity ratio of thermally coupled energy levels (²H_11/2 and ⁴S_3/2 to the ground state energy level ⁴I_15/2) of Er³⁺ ions in Ba₂MgWO₆, BaSrMgWO₆ and Sr₂MgWO₆. The maximum absolute sensitivities obtained for Ba₂MgWO₆, BaSrMgWO₆ and Sr₂MgWO₆ doped with 7% Er³⁺, 2% Yb³⁺ and 9% K⁺ were 6.77 × 10^-4 K^-1, 10.09 × 10^-4 K^-1 and 23.4 × 10^-4 K^-1, respectively. The comparison revealed that the phase transition caused an increase in the luminescence intensity and absolute sensitivity. This provides a useful pathway for modulating the subsequent thermometric performance.

NIR light guided enhanced photoluminescence and temperature sensing in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor

The conversion of NIR light into visible light has been studied in Ho3+/Yb3+/Bi3+ co-doped ZnGa2O4 phosphor for the first time. The crystallinity and particles size of the phosphor increase through Bi3+ doping. The absorption characteristics of Ho3+, Yb3+ and Bi3+ ions are identified by the UV-vis-NIR measurements. The Ho3+ doped phosphor produces intense green upconversion (UC) emission under 980 nm excitations. The emission intensity ~ excitation power density plots show contribution of two photons for the UC emissions. The UC intensity of green emission is weak in the Ho3+ doped phosphor, which enhances upto 128 and 228 times through co-doping of Yb3+ and Yb3+/Bi3+ ions, respectively. The relative and absolute temperature sensing sensitivities of Ho3+/Yb3+/5Bi3+ co-doped ZnGa2O4 phosphor are calculated to be 13.6 × 10-4 and 14.3 × 10-4 K-1, respectively. The variation in concentration of Bi3+ ion and power density produces excellent color tunability from green to red via yellow regions. The CCT also varies with concentration of Bi3+ ion and power density from cool to warm light. The color purity of phosphor is achieved to 98.6% through Bi3+ doping. Therefore, the Ho3+/Yb3+/Bi3+:ZnGa2O4 phosphors can be suitable for UC-based color tunable devices, green light emitting diodes and temperature sensing.

First-Principles Calculation of Photoelectric Property in Upconversion Materials through In3+ Doping

Multicolor turning holds great promise in optical intelligent recognition and optical imaging. Here, Er³⁺, Yb³⁺, and In codoped ZnO (Er/Yb/IZO) with a uniform block strucuture is obtained. The doping of In³⁺ ions enhances the multicolor upconversion luminescence (UCL) intensity of Er/Yb/IZO. Particularlly, the UCL of Er/Yb/I₂ZO turns from red through yellow to dominant green emission via increasing density power from 2.54 to 10.19 W/cm², thus realizing the power sensitiviy. First-principles theory is used to design a In³⁺, Yb³⁺, and Er³⁺ codoped ZnO. The band structure, total density of state and optical coefficient of Er/Yb/IZO have been studied via a generalized gradient approximation within density functional theory (DFT). The potential electron density and total electron density of the O atom increase with In³⁺ and Er³⁺/Yb³⁺ doping, which indicate that substitution of Zn²⁺ by In³⁺ and Er³⁺/Yb³⁺ generate positive vacancies on the surface. The band gap of Er/Yb/IZO decreases compare with that of pure ZnO. Furthermore, the optical coefficient of In³⁺ doping is enhanced compare with that of pure ZnO via using DFT calculations.

Zero-concentration quenching: a novel Eu3+ based red phosphor with non-layered crystal structure for white LEDs and NaSrY(MoO4)3:Sm3+ based deep-red LEDs for plant growth

Oxide based highly efficient narrow band red emitting phosphors are still a bottleneck in white LED applications. Trivalent europium ion based phosphors could be a better choice, however their weak oscillator strength restricts their use in white light emitting diodes (LEDs). Herein, we report a novel red emitting NaSrEu(MoO₄)₃ (NSEuM) phosphor with zero concentration quenching (non-layered crystal structure). The phosphors (NaSrY_1-xEu_x(MoO₄)₃, x = 0.1-1, in increments of 0.1) were synthesized through a traditional solid-state reaction and their phase formations were analyzed by powder X-ray diffraction (PXRD) followed by Rietveld refinement. Under 395 nm excitation, all the phosphors showed sharp emission at 616 nm (full width at half maximum, FWHM ∼4-5 nm) owing to the ⁵D₀→⁷F₂ electric dipole transition of the Eu³⁺ ion. A concentration dependent photoluminescence (PL) study revealed that there is no concentration quenching of the systems, leading to them having superior emission characteristics over those of commercial red phosphors as well as a reported Eu³⁺ phosphor with a layered structure. The color purity of the synthesized phosphor was observed to be 96.32% and it shows excellent thermal stability at 423 K, retaining 64.6% of the emission intensity of its initial room temperature. The NSEuM phosphor shows a high absolute quantum yield of 79.7%. Besides this, a red LED (near UV (NUV) LED chip with the NaSrEu(MoO₄)₃ phosphor) as well as a hybrid white LED (NUV LED chip with an organic yellow dye + red NSEuM phosphor) were fabricated and their optical properties were studied. After the inclusion of the red phosphor in the hybrid white LED, the color rendering index (CRI)/correlated color temperature (CCT) were improved significantly (60/9333 K vs. 79/6004 K, respectively). In addition, to show the potential use of the system in plant growth application, we systematically investigated the Sm³⁺ activation in NaSrY(MoO₄)₃ and found that the phosphor shows orange red emission with an intense deep red emission (645 nm (⁴G_5/2→⁶H_9/2)). We fabricated a hybrid red/deep red LED by integrating a NUV LED with a mixed Sm³⁺ and Eu³⁺ phosphor and the spectral lines were well matched with the phytochrome (Pr) absorption spectrum. The presently investigated phosphor showed potential in a white LED as well as a deep red/orange-red LED for plant growth.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

Achieving high thermal stability of different rare-earth ions in a single matrix host via the manipulation of the local structure by a solid solution

Thermal quenching seriously restricts the practical application of phosphors, particularly under high temperature and long-term working conditions. Here, we demonstrate that the as-obtained series of solid solutions of Ca2-xYxAl2Si1-xAlxO7:Tb3+ (x = 0-1, Ca2Al2SiO7 → CaYAl3O7) phosphors exhibit an adjustable optical performance, where CaYAl3O7:Tb3+ exhibits a greatly improved thermal stability with a shortened bond distance of the related polyhedron compared with Ca2Al2SiO7:Tb3+. The shrunken bond distance strengthens the pressure of the local structure and suppresses the non-radiative transition effectively, contributing to the prevention of the thermal degradation. The formed phosphor with excellent structural stability could be effectively incorporated with various lanthanide ions (Eu3+, Tb3+, Sm3+, Dy3+, and Pr3+) to address a pleochroism output.

High performance red/deep-red emitting phosphors for white LEDs

NaSrGd(MoO₄)₃:Eu³⁺ red phosphor exhibits higher quantum efficiency (82%) and the fabricated white LED showed 74% CRI and 6823 K CCT.

nanocrystals (0 ≤ x ≤ 1): growth, size control and shell formation on β-NaCeF4:Tb core particles

is an interesting shell material for β-NaREF₄ particles of the lighter lanthanides (RE = Ce, Pr, Nd), as variation of its strontium content x allows to vary its lattice parameters and match those of the core material.

An efficient down conversion luminescencent probe based on a NaGdF4:Eu3+/Ce3+ nanophosphor for chemical sensing of heavy metal ions (Cd2+, Pb2+ and Cr3+) in waste water

Eu³⁺ doped and Eu³⁺/Ce³⁺ co-doped NaGdF₄ nanophosphors are fabricated via a facile hydrothermal route. The codoped counterpart is demonstrated for efficient photoluminescence sensing of heavy metal ions (Cd²⁺, Pb²⁺ and Cr³⁺) present in industrial effluents.

Temperature-sensing luminescent materials La9.67Si6O26.5:Yb3+–Er3+/Ho3+ based on pump-power-dependent upconversion luminescence

Rare earth ion doped upconversion (UC) luminescent materials could show potential applications in optical temperature sensing.

Rare-earth (Gd3+,Yb3+/Tm3+, Eu3+) co-doped hydroxyapatite as magnetic, up-conversion and down-conversion materials for multimodal imaging

Taking advantage of the flexibility of the apatite structure, nano- and micro-particles of hydroxyapatite (HAp) were doped with different combinations of rare earth ions (RE³⁺ = Gd, Eu, Yb, Tm) to achieve a synergy among their magnetic and optical properties and to enable their application in preventive medicine, particularly diagnostics based on multimodal imaging. All powders were synthesized through hydrothermal processing at T ≤ 200 °C. An X-ray powder diffraction analysis showed that all powders crystallized in P6₃/m space group of the hexagonal crystal structure. The refined unit-cell parameters reflected a decrease in the unit cell volume as a result of the partial substitution of Ca²⁺ with smaller RE³⁺ ions at both cation positions. The FTIR analysis additionally suggested that a synergy may exist solely in the triply doped system, where the lattice symmetry and vibration modes become more coherent than in the singly or doubly doped systems. HAp:RE³⁺ optical characterization revealed a change in the energy band gap and the appearance of a weak blue luminescence (λ_ex = 370 nm) due to an increased concentration of defects. The "up"- and the "down"-conversion spectra of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders showed characteristic transitions of Tm³⁺ and Eu³⁺, respectively. Furthermore, in contrast to diamagnetic HAp, all HAp:RE³⁺ powders exhibited paramagnetic behavior. Cell viability tests of HAp:Gd/Yb/Tm and HAp:Gd/Eu powders in human dental pulp stem cell cultures indicated their good biocompatibility.

Photon-Upconversion Barcoding with Multiple Barcode Channels: Application for Droplet Microfluidics

Barcoding facilitates high-throughput analytical methods in complex matrixes with a reduced volume of sample, reagents, time, and cost. Because of orthogonality to fluorescence, photon-upconversion barcodes attracted considerable attention in recent years. We constructed an epiluminescence detector, which, for the first time, demonstrated the reading of photon-upconversion spectra from microdroplets in a microfluidic chip with frequency up to 10 Hz. Non-negative least-squares deconvolution enabled the reading of an unprecedented number of photon-upconversion barcode channels (six) from emission spectra (excitation 980 nm, emission 430-875 nm). The standard deviation of barcode reading from microdroplets was ∼1%. Described barcoding can be, for example, used for multiparameter titrations, multiplexed biological and chemical assays, optimizations on a microfluidic platform, and preparation of barcoded concentration gradients and libraries.

Anti-Stokes Ultraviolet Luminescence and Exciton Detrapping in the Two-Dimensional Perovskite (C6H5C2H4NH3)2PbCl4

Recently, it has been found that low-dimensional organometallic halide perovskites can be adopted as nonlinear monolayer emitters because of their efficient spontaneous anti-Stokes visual luminescence under visual or near-infrared laser excitation. Herein, we demonstrate a luminescence up-conversion process from the visible self-trapped exciton (STE) to an ultraviolet (UV) free exciton (FE) in the two-dimensional perovskite (C₆H₅C₂H₄NH₃)₂PbCl₄ quantum wells excited by nanosecond pulse laser excitation. An ultraviolet 347 nm near-band-edge FE emission is obtained under the excitation of 579 nm dye laser at 10 K by a two-step, two-photon absorption process from the real intermediate exciton state. In addition, the decay rise time of higher-laying states of STE indicates the excitonic detrapping procedure could occur by the annihilation of phonons. Our results suggest that the low-dimensional halide perovskites with deformable structure are able to be applied in visible light-pumped UV-emitting devices.

Concentration and pump power-mediated color tunability, optical heating and temperature sensing via TCLs of red emission in an Er3+/Yb3+/Li+ co-doped ZnGa2O4 phosphor

The Er³⁺/Yb³⁺/Li⁺ co-doped ZnGa₂O₄ phosphor gives intense red upconversion photoluminescence, color tunability with Er³⁺ ion concentration and incident pump power, R/G ratio, induced optical heating and temperature sensing characteristics.

Cannabis sativa-derived carbon dots co-doped with N–S: highly efficient nanosensors for temperature and vitamin B12

Cannabis sativa-derived carbon dots as efficient nanosensors for temperature and vitamin B₁₂.

Tungsten doped hydroxyapatite processed at different temperatures: dielectric behaviour and anti-microbial properties

Electrical and antibacterial activities of bio-compatible W/HAp synthesizedviachemical precipitation followed by annealing at different temperature.

Multifunctional GdVO4:Eu core–shell nanoparticles containing 225Ac for targeted alpha therapy and molecular imaging

Development of actinium-225 doped Gd_0.8Eu_0.2VO₄ core–shell nanoparticles as multifunctional platforms for multimodal molecular imaging and targeted radionuclide therapy.