Lanthanide-Functionalized Metal−Organic Framework as Ratiometric Probe for Selective Detection of 4-NA and Fe3+

Luminescent MOFs with dual or multiple emission centers can act as multi-target and self-calibrating probes to selectively detect environment pollutants with high precision. In this paper, we synthesized Ln³⁺@Zn-MOF (Ln³⁺ = Eu³⁺ and Tb³⁺) with dual emission characteristics by post-encapsulation Ln³⁺ ions into Zn-MOF. The fluorescence sensing experiments show that Eu³⁺@Zn-MOF can be used as a multi-functional and self-calibrating probe to selectively detect 4-nitroaniline (4-NA) and Fe³⁺ ions with high sensitivity, good anti-interference and repeatability. The LOD is 6.01 μM and 60.99 μM for 4-NA and Fe³⁺ ions, respectively. Compared to the pristine Zn-MOF, Eu³⁺@Zn-MOF exhibits the higher sensitivity and accuracy in detection application. Further studies on UV–vis adsorption spectra show that the possible fluorescence quenching mechanism are the competitive absorption of excitation light between MOF and the analytes. And this work presents a promising strategy to prepare dual emissions probes for effective detection of environment pollutants.

     

Ca2Na2La6(SiO4)4(PO4)2O: Eu2+/Eu3+: A visual dual-emitting fluorescent ratiometric temperature sensor

A novel apatite-based UV-excited dual-emitting Ca₂Na₂La₆(SiO₄)₄(PO₄)₂O: Eu²⁺/Eu³⁺ phosphor (CNL: Eu²⁺/Eu³⁺) was designed and successfully synthesized by a solid-state reaction. Compared with previous reports on this family of materials, a structural study based on DFT calculation exhibited a new consequence that the monovalent ions in this system are more inclined to occupy the seven-coordinate cationic sites rather than the nine-coordinate sites. This result was confirmed by the structural refinement and high-resolution transmission electron microscopy (HRTEM) data. Due to the coexistence of Eu²⁺ and Eu³⁺ dopants in the material, under 345 or 392 nm excitation, CNL: 0.02Eu²⁺/Eu³⁺ exhibited a green Eu²⁺ emission band (528 nm) and red Eu³⁺ emission peaks (around 618 nm). The application potential of CNL:0.02Eu²⁺/Eu³⁺ in luminescent thermometry was studied by exploiting the temperature sensitivity of the fluorescent intensity ratio (green/red) at different temperatures. It was found that, under 345 nm excitation, the fluorescent intensity ratio of CNL: 0.02Eu²⁺/Eu³⁺ displayed linear correlation over the temperature range of 298 to 473 K with a high sensitivity of 2.82%K⁻¹. Additionally, the emission color of the CNL: 0.02Eu²⁺/Eu³⁺ sample under UV lamp (254 and 365 nm) excitation showed an obvious change (from green to red) as the temperature increased from 298 to 473 K (from green to red). These results indicated that CNL: Eu²⁺/Eu³⁺ can serve as an excellent visual luminescent ratiometric thermometer. Furthermore, this work provides a novel reference for developing high-performance luminescence temperature-sensing materials.     

Facile synthesis of Sr2+-doped LaVO4:Eu3+ nanostructures: Morphology evolution,luminescence modulation and turn-off fluorescent probe for selectively detecting Cu2+ ions with high sensitivity

In this work, the two-phase Sr²⁺-doped LaVO₄:Eu³⁺ nanomaterials were constructed through a facile hydrothermal approach. The crystal phase, morphology and optical performance were systematically investigated in detail. The results manifested that the dopant Sr²⁺ ions were doped into the host lattice, restricting the growth of grain and elevating the fluorescence intensity simultaneously. The morphology evolution process and optical performance modulation were also fully analysed. The fluorescence quenching was attributed to the adsorption of Cu²⁺ ions onto the matrix surface by electrostatic attraction and succeeding energy transfer from Eu³⁺ to Cu²⁺. Moreover, the materials displayed an excellent detecting ability for Cu²⁺ with high selectivity and sensitivity (0.514 μM and 0.476 μM for both two-phase samples). Consequently, this material could be applied as a promising candidate for Cu²⁺ detection due to good reusability and facile synthesis.     

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

Intense red emission via energy transfer from (Ce3+/Eu3+):P2O5+NaF+CaF2+AlF3 glasses for warm light sources

Europium (Eu³⁺)-doped fluorophosphate (PNCA:P₂O₅+NaF + CaF₂+AlF₃) glasses with the addition of cerium (Ce³⁺) ions were fabricated by the melt-quenching technique to know their ability for the bright red (615 nm) luminescence. The emission (PL) and excitation (PLE) spectra, decay curve measurements as well as energy transfer (ET) process of Ce³⁺→ Eu³⁺ were studied in detail. An excitation spectrum related to the ⁷F₀→ ⁵D₂ level of Eu³⁺ is used to estimate the phonon energy (1121 cm^?1) of the title glass host. Under ultraviolet (UV) irradiation of 299 nm, the PL spectra of (Ce³⁺/Eu³⁺):PNCA glasses show intense red emission at 615 nm whereas the lifetime decrease with respect to increase of Eu³⁺ that could support the observed efficient ET from Ce³⁺ to Eu³⁺. The ET:Ce³⁺ →Eu³⁺ via quadrupole-quadrupole process was confirmed by Reisfeld's approximation and Dexter's ET formula. The ET efficiency (η_ET) and critical distance (R_c) were also calculated. Interestingly, the (Ce³⁺/Eu³⁺):PNCA glasses showed intense red light emission with low correlated color temperatures and the corresponding color purity reached as great as 99%, indicating its potentiality as a red component for warm light sources.     

Ce3+ induced broadband enhancement around 2 μm in Tm3+/Ho3+ co-doped tellurite glass

Tellurite glasses doped with Tm³⁺, Ho³⁺ and Ce³⁺ ions were prepared via melt-quenching to realise broadband and fluorescence enhancement in near-infrared (NIR) band. Under the pumping of a commercial 808 nm laser diode (LD), the emission bands at 2.0 μm, 1.85 μm, 1.47 μm, and 705 nm were observed in the Tm³⁺/Ho³⁺ co-doping glass samples, which originated from the transitions of Ho³⁺:⁵I₇→⁵I₈ and Tm³⁺:³F₄→³H₆, ³H₄→³F₄, ³F_2,3 → ³H₆, respectively. The existence of 2.0 μm band fluorescence is due to the energy transfer from the Tm³⁺:³F₄ level to the Ho³⁺:⁵I₇ level. This band overlaps with the 1.85 μm band which forms a broadband fluorescence spectrum in the range of 1600–2200 nm. In glass samples co-doped with Tm³⁺/Ho³⁺ with 0.085 mol% Ho₂O₃ and 1 mol% Tm₂O₃, the full width at half maximum (FWHM) of this broadband spectrum (1600–2200 nm) was as high as ∼370 nm. After introducing 0.6 mol% CeO₂, the emission intensity of broadband fluorescence increased by ∼50%, which was caused by the cross-relaxations between Ce³⁺ and Tm³⁺ ions. The lifetime of fluorescence decay was determined to prove the interactions among the doped rare-earth ions, the radiative parameters such as transition probability, branching ratio and radiative lifetime were calculated from the absorption spectra based on the Judd-Ofelt theory to better understand the observed luminescence phenomena. In addition, X-ray diffraction (XRD) confirmed the amorphous state structure of the synthesised glass samples, while Raman spectrum revealed the different vibrational structural units forming the glass network.     

Improving white light emission and quantum yield of Ce@Eu co-doped silicate glass by reducing Eu3+ to Eu2+ with Si3N4

Rare-earth-doped transparent glass shows great potential in white light-emitting diodes (wLEDs) application due to its excellent optical and luminous properties. Currently reported commercial wLEDs have a drawback in red emission missing, which leads to a relatively low color rendering index (CRI) and a relatively high correlated color temperature (CCT). In this work, Ce@Eu Sr–Si–O glass is fabricated using a high-temperature quenching method. The white light is available when the ratio of Ce³⁺/Eu³⁺ equals 1, and the emitting color can be adjusted from blue to red by controlling the ratio of Ce³⁺/Eu³⁺. To further optimize the white light, Eu³⁺ ions can be reduced to Eu²⁺ according to the reaction of 6Eu³⁺ + 2N³⁻ → 6Eu²⁺ + N₂↑ by introducing Si₃N₄. As a result, the standard white light emission can be achieved in the Ce@Eu silicate glass contributed by the blue light from Ce³⁺, red light from Eu³⁺, and yellow–green light from Eu²⁺ (two elements, three emission). This glass shows excellent luminous properties, such as a color coordinate is (0.3651, 0.3269) in CIE 1931 color coordinate diagram, a CRI is over 70, a high quantum yield of 36.02%, and a CCT of 4117 K.     

Eu2+ activated novel eulytite Na3Bi5(PO4)6: Eu3+ phosphors: Enhanced luminescence and thermal stability for photonics application

For the first time, novel eulytite-like Eu²⁺/Eu³⁺: Na₃Bi₅(PO₄)₆ phosphor was synthesized via high temperature solid-state reaction method in reduction environment, and the structure, luminescence performances and thermal stability were investigated and discussed using various techniques. X-ray refinement diffraction and Raman spectra revealed the around 200 nm well-crystallized eulytite-type (I43d space group) phosphors were synthesized, and a diagram of crystal structure of Na₃Bi₅(PO₄)₆ was proposed. X-ray photoelectron spectroscopy analysis confirmed the co-existence of Eu²⁺ and Eu³⁺ ions which exhibited characteristic 4f⁶5d→⁸S_7/2 transition of Eu²⁺ and ⁷F₀→⁵D_0,1,2,3,4 transitions of Eu³⁺ ions. On the other hand, due to the activation of Eu²⁺, samples displayed good tunability on excited and emission behaviors under different excited laser. The JO parameters, emission cross-section, branching ratio and asymmetric ratio indicated that the Eu doping increased the covalency and asymmetry of host. Thermal quenching was studied and the reasons were discussed. Through the comparison of phosphors prepared in different conditions, the thermal stability& repeatability, radiative lifetime, color purity and activation energy were remarkably superior due to the Eu doping and in particularly Eu²⁺ activation. Finally, the energy level and CIE chromaticity diagrams were plotted to explain the mechanism of Eu²⁺ activation and energy transfer between Eu²⁺ and Eu³⁺ ions. The 0.5%Eu doped Na₃Bi₅(PO₄)₆ exhibited promising tunable red-emission performance with quantum efficiency of 92%, activation energy of 0.24 eV, red color purity of 93.74% and very low non-radiative transfer ratio 44.20 s^?1 with smaller CCT (<2200 K).     

Near-UV light excited Eu3+, Tb3+, Bi3+ co-doped LaPO4 phosphors: Synthesis and enhancement of red emission for WLEDs

A series of single-phase Eu³⁺, Tb³⁺, Bi³⁺ co-doped LaPO₄ phosphors were synthesized by solid-state reaction at 800 °C. Crystal structures of the phosphors were investigated by X-ray diffraction (XRD). A monoclinic phase was confirmed. The excitation (PLE) and emission (PL) spectra showed that the phosphors could emit red light centered at 591 nm under the 392 nm excitation, which is in good agreement with the emission wavelength from near-ultraviolet (n-UV) LED chip (370–410 nm). The results of PLE and PL indicated that the co-doped Tb³⁺ and Bi³⁺could enhance emission of Eu³⁺ and the fluorescent intensities of the phosphors excited at 392 nm could reach to a maximum value when the doping molar concentration of Tb³⁺ and Bi³⁺ is about 2.0% and 2.0%, respectively. The co-doping Tb³⁺ and Bi³⁺ ions can strengthen the absorption of near UV region. They can also be efficient to sensitize the emission of Eu³⁺, indicating that the energy transfer occurs from Tb³⁺ and Bi³⁺ to Eu³⁺ ions. From further investigation it can be found that co-doping Tb³⁺ and Bi³⁺ ions can also induce excitation energy reassignment between ⁵D₀–⁷F₁ and ⁵D₀–⁷F₂ in these phosphors, and result in more energy assignment to ⁵D₀–⁷F₂ emission in LaPO₄:Eu³⁺, Tb³⁺, Bi³⁺. Our research results displayed that La_0.94PO₄:Eu³⁺_0.02, Tb³⁺_0.02, Bi³⁺_0.02 could be a new one and could provide a potential red-emitting phosphor for UV-based white LED.     

Gel-combustion assisted synthesis of eulytite-type Sr3Y(PO4)3 as a single host for narrow-band Eu3+ and broad-band Eu2+ emissions

A series of eulytite-type Sr₃Y_1-x(PO₄)₃:xEu³⁺ (x = 0–0.13) and Sr_3-yY(PO₄)₃:yEu²⁺ (y = 0–0.10) phosphors were successfully synthesized via gel-combustion and subsequent calcination in O₂ and Ar/H₂ atmospheres at 1250 °C, respectively. Detailed crystal structure analysis via Rietveld refinement showed that the phosphors were crystallized in the cubic system (space group I-43d, No. 220), in which the Eu³⁺ and Eu²⁺ activators reside at the Y³⁺ and Sr²⁺ sites, respectively. The trivalent Eu³⁺ ions (CN = 6) exhibited typical narrow-band luminescence via intra-4f⁶ transitions, with the red emission at ~ 615 nm being dominant (⁵D₀ → ⁷F₂ transition, FWHM = 15.9 ± 0.2 nm). The divalent Eu²⁺ ions (CN = 6 and 9) showed broad-band luminescence ranging from light-blue to blue via 4f⁶5d¹ → 4f⁷ transitions (FWHM = 115 ± 2 nm). The optimal Eu³⁺ and Eu²⁺ concentrations were determined to be 10 at% (x = 0.10) and 7 at% (y = 0.07), respectively, and the mechanisms of concentration quenching were discussed. The excitation/emission properties, fluorescence decay kinetics, CIE chromaticity, and particularly the rarely addressed thermal stability of the phosphors were investigated in detail.     

Impact of Eu3+ Dopants on Optical Spectroscopy of Ce3+: Y3Al5O12‐Embedded Transparent Glass‐Ceramics

Transparent glass‐ceramics containing Ce³⁺: Y₃Al₅O₁₂ phosphors and Eu³⁺ ions were successfully fabricated by a low‐temperature co‐sintering technique to explore their potential application in white light‐emitting diodes (WLEDs). Microstructure of the sample was studied using a scanning electron microscope equipped with an energy dispersive X‐ray spectroscopy. The impact of co‐sintering temperature, Ce³⁺: Y₃Al₅O₁₂ crystal content and Eu³⁺ doping content on optical properties of glass‐ceramics were systematically studied by emission, excitation spectra, and decay curves. Notably, the spatial separation of these two different activators in the present glass‐ceramics, where Ce³⁺ ions located in YAG crystalline phase while the Eu³⁺ ones stayed in glass matrix, is advantageous to the realization of both intense yellow emission assigned to Ce³⁺: 5d→4f transition and red luminescence originating from Eu³⁺: 4f→4f transitions. As a result, the quantum yield of the glass‐ceramic reached as high as 93%, and the constructed WLEDs exhibited an optimal luminous efficacy of 122 lm/W, correlated color temperature of 6532 K and color rendering index of 75.     

Luminescence and temperature-sensing properties of Y4GeO8:Bi3+,Eu3+ phosphor

In this paper, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor with dual emission centers was elaborated via conventional solid-state reaction technology. Thorough research on the structure, morphology, and luminous properties of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor, the potential applications in optical thermometry were investigated by means of fluorescence intensity ratio and thermochromic techniques. Under 290 and 347 nm excitation, Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor presents broadband emission from ³P₁ → ¹S₀ transition of Bi³⁺ ions and characteristic emission peaks from 4f–4f transition of Eu³⁺ ions. Outstanding temperature-sensing capabilities are acquired from Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor. The maximum relative sensitivity (S_r) can attain 1.51% K⁻¹ (λ_ex = 290 nm). With temperature raising (303–513 K), the emitted color of Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor (λ_ex = 290 nm) shifts from faint yellow to red with a high chromaticity shift (0.180), which can be distinguished by the unaided eye clearly. Our results indicate that Y₄GeO₈:Bi³⁺,Eu³⁺ phosphor has potential applications in optical temperature measurement and high-temperature safety marker.     

Eu3+‐Activated Borogermanate Scintillating Glass with a High Gd2O3 Content

Eu³⁺‐activated borogermanate scintillating glasses with compositions of 25B₂O₃–40GeO₂–25Gd₂O₃–(10?x)La₂O₃–xEu₂O₃ were prepared by melt‐quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X‐ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd₂O₃ is of significance for designing dense glass. Furthermore, energy‐transfer efficiency from Gd³⁺ to Eu³⁺ ions can be near 100% when the content of Eu₂O₃ exceeds x = 4, the corresponding critical distance for Gd³⁺–Eu³⁺ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu³⁺ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu₂O₃. The degree of Eu–O covalency and the local environment of Eu³⁺ ions are evaluated by the value of Ω_t parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu–O bond increases with the increasing concentration of Eu³⁺ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X‐ray excitation is found to be in the case of 6 mol% Eu₂O₃, which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X‐ray energy.     

Enhanced 2.0 μm Emission and Lowered Upconversion Emission in Fluorogermanate Glass‐Ceramic Containing LaF3:Ho3+/Yb3+ by Codoping Ce3+ Ions

Intense 2.0 μm emission of Ho³⁺ has been achieved through Yb³⁺ sensitization in fluorogermanate glass‐ceramic (GC) containing LaF₃ pumped with 980 nm laser diode (LD). The observation of concurrent emissions at 538, 650, and 1192 nm points to the additional deexcitation routes based on infrared‐to‐visible upconversion processes and Ho³⁺:⁵I₆ → ⁵I₈ radiative transition. Comparative investigations of photoluminescent spectra and decay curves have indicated the effective role of Ce³⁺ ions in enhancing the 2.0 μm fluorescence along with suppressing the occurrence of these concurrent emissions. This would offer a promising approach to develop compact and efficient 2.0‐μm laser systems.     

Impact of the A-site rare-earth ions (Ln3+ – Sm3+, Eu3+, Gd3+) on structure and electrical properties of the high entropy LnCr0.2Mn0.2Fe0.2Co0.2Ni0.2O3 perovskites

High entropy perovskites LnCr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2O₃ ceramics were produced by solid-state reactions from oxides. The B-site chemical composition was fixed (Cr_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2) and A-site composition was varied by the rare-earth ions (Ln = Sm³⁺, Eu³⁺ and Gd³⁺). The entropy of B-sublattice mixing was 1.609R J/(mol*K). The dependences of the lattice parameters, microstructure features, and electrical properties were discussed as function of the A-site rare-earth ions. The correlation of the lattice parameters with the nature of the A-site rare earth ions was demonstrated. Impact of the rare-earth ions in A-site on microstructural parameters was observed. Charge conduction mechanisms were discussed in details for a wide range of temperatures.     

Uniform colloidal spheres for RE3BO6 (RE = Eu-Yb,Y) and excitation-dependent luminescence of Y3BO6:Eu3+ red phosphor

Phosphor particles of spherical shape and uniform size are desired for high-definition displays to improve the resolution and the overall luminescent performance. However, the synthesis of RE₃BO₆ spherical particles is a considerable challenge in materials science. Here, uniform spheres of RE₃BO₆ (RE = Eu–Yb, Y) have been converted from their colloidal precursor spheres synthesized via homogeneous precipitation. The amorphous precursor spheres are solid particles with decreased boron going from the surfaces to the cores. Smaller particles were observed at decreased ionic radius from Eu³⁺ to Ho³⁺ (including Y³⁺), but particles with nearly unvaried sizes were observed by further decreasing the ionic radius from Ho³⁺ to Yb³⁺. They crystallized in monoclinic RE₃BO₆ at 900°C, with maintaining the spherical shape of precursors. However, the crystal growth and the densification toward the particle surfaces resulted in the formation of hollow spheres for smaller particles and core-shell structured spheres for larger particles. The parameters, a, b, and c, increase nearly monotonically with increasing the radius of rare earth ions. The uniform spheres of Y₃BO₆:Eu³⁺ exhibited a typical red emission at ~613 nm (⁵D₀ → ⁷F₂ electric dipole transition of Eu³⁺), with an intensity ratio I(⁵D₀ → ⁷F₂)/I(⁵D₀ → ⁷F₁) of ~3.5. The luminescence behavior of Y₃BO₆:Eu³⁺ phosphor is dependent on the excitation wavelength, which is closely related to the Eu³⁺ ions at different coordination sites. Driven by a 460-nm blue-LED chip, the Y₃BO₆:Eu³⁺ spheres exhibited a red emission with the CIE coordinates of (~0.65, ~0.35), indicating that they are an excellent red-emitting phosphor candidate for application in white-LEDs.     

Spectroscopic and energy transfer mechanism of Er3+, Pr3+-codoped ZBYA glass

Absorption spectra, emission spectra and the rate parameters of the energy-exchange processes relevant to the ⁴I_11/2→⁴I_13/2 laser transition in Er³⁺/Pr³⁺- codoped ZBYA(ZrF₄–BaF₂–AlF₃–YF₃) glass were presented. Intensive 2.7 μm emission was obtained in the codoped glass and the optimized concentration ratio of Pr³⁺ to Er³⁺ was found to be 0.1:1. With the presence of Pr³⁺ ions, the intensities of the green and near-infrared emission were dramatically reduced to 1/15 and 1/21, respectively. The Er³⁺/Pr³⁺-codoped sample was found to have higher predicted spontaneous transition probability (16.57%) along with larger calculated emission cross section (14.6×10⁻²¹ cm²). These results suggest that the 2.7 μm emission of Er³⁺ ions could be achieved in ZBYA glass and codoping with Pr³⁺ could greatly improve the mid-infrared emission performance.     

A novel Eu2+/Tb3+ co-doped phosphor with pyroxene structure applied for cryogenic thermometric sensing

Pyroxene-type phosphors were widely developed due to the advantages of high chemical stability, luminous efficiency, and low production cost. In this contribution, a series of Eu²⁺/Tb³⁺ co-doped Ca_0.75Sr_0.2Mg_1.05Si₂O₆ (CSMS) phosphors with pyroxene structure were successfully synthesized by the solid-state method. Under the 340 nm excitation, the emission peaks of the phosphor show a redshift with the increase of Eu²⁺ concentration. The emitting color of Eu²⁺/Tb³⁺ co-doped samples shows a redshift attributed to the energy transfer from Eu²⁺ to Tb³⁺. Simultaneously, acquired thermometer exposes superbly temperature-sensitive properties (S_a and S_r having maximum values 4.7% K⁻¹ and 0.6% K⁻¹, respectively) over the cryogenic temperature range (77–280 K). Furthermore, it has good stability and precision at cryogenic temperatures, indicating that CSMS:0.03Eu²⁺/0.03Tb³⁺ phosphor is a very promising fluorescent material suitable for cryogenic temperature sensing.     

Luminescence properties of Ca2GdNbO6: Sm3+, Eu3+ red phosphors with high quantum yield and excellent thermal stability for WLEDs

A series of Ca₂GdNbO₆: xSm³⁺ (0.01 ≤ x ≤ 0.15) and Ca₂GdNbO₆: 0.03Sm³⁺, yEu³⁺ (0.05 ≤ y ≤ 0.3) phosphors were synthesized by the traditional solid-state sintering process. XRD and the corresponding refinement results indicate that both Sm³⁺ and Eu³⁺ ions are doped successfully into the lattice of Ca₂GdNbO₆. The micro-morphology shows that the elements of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor are evenly distributed in the sample, and the particle size is about 2 μm. The optical properties and fluorescence lifetime of Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors were detailedly studied. The emission peak at ⁵D₀→⁷F₂ (614 nm) is the strongest and emits red light under 406 nm excitation. The increase of Eu³⁺ concentration causes the energy transfers from Sm³⁺ to Eu³⁺ ions, and the transfer efficiency reaches 28.6%. Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphor has a quantum yield of about 82.7%, and thermal quenching activation energy is of 0.312 eV. The color coordinate (0.646, 0.352) of Ca₂GdNbO₆: 0.03Sm³⁺, 0.2Eu³⁺ phosphors is located in the red area. The LED device fabricated based on the above phosphor emit bright white light, and CCT = 5400 K, Ra = 92.8. The results present that Ca₂GdNbO₆: 0.03Sm³⁺, Eu³⁺ phosphors potentially find use in the future.     

Study of Eu3+–Gd3+ co-doped Ba–Bi–B glasses for red-laser applications: Physical,structural, photoluminescence and time-resolved spectral characteristics

A series of Eu³⁺ and Eu³⁺/Gd³⁺ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd³⁺ to Eu³⁺ ions. The density of glasses increased with increasing of Gd³⁺ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu³⁺-Gd³⁺ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu³⁺: ⁵D₀→ ⁷F₂ transition. Less intense emissions centered at 577 nm (⁷F₀), 590 nm (⁷F₁), 651 nm (⁷F₃) and 700 nm (⁷F₄) are also observed from the radiative transitions of the excited state ⁵D₀ of Eu³⁺ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu³⁺ and 3.0 mol% Gd³⁺ co-doped glass under λ_Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications.