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Strong Mn─Mn coupling interactions, including dipolar and exchange interactions, significantly affect the photoluminescence quantum yields (PLQYs) in Mn2+‐based luminescent materials. However, clarifying the individual effects of dipole–dipole and exchange interactions on photoluminescence (PL) is challenging because these interactions may have similar effects on PL properties, and there is a lack of materials with precisely tunable Mn─Mn distances over a wide range. In this study, the influence of dipolar and exchange coupling on PLQY is quantitatively decoupled by designing a series of hybrid manganese chlorides single crystals with a wide tuning range of Mn─Mn distances, from 6.0 to 9.5 Å. It is found that the PLQY can be enhanced from 2.1% to 57.1%, and the PL lifetime increased from 0.21 to 3.81 ms as the Mn─Mn distance increased. This enhancement is solely attributed to the decreased energy transfer dominated by dipole–dipole interactions. At the shortest Mn─Mn distance of 6 Å, exchange coupling becomes dominant, resulting in an additional red‐side PL band with negligible effects on PLQY and lifetime. This work provides valuable insights into the mechanisms underlying the regulation of PLQY in Mn2⁺‐based luminescent materials. [ABSTRACT FROM AUTHOR]

NIR‐II luminescent materials are the key enablers of smart spectroscopy‐based techniques, offering capabilities for nondestructive analysis and bio‐imaging. Here, a broadband NIR‐II luminescence with a recorded external quantum efficiency (EQE) of 76% in LiGa5O8 are demonstrated, using heavily doping Cr3+ ion (10%) as a light harvester and a controllable energy transfer (ET) from Cr3+ to Ni2+ (0.4%) ions. Even though the Cr3+ ion produces substantially weak luminescence due to concentration quenching, the introduction of Ni2+ ions effectively extract the excitation energy to generate NIR‐II luminescence. Complementary investigations using synchrotron‐based EXAFS fittings and structural refinement disclose a significant structural distortion in the LiGa5O8 compound, which facilitates the relaxation of the parity‐selection rules for Cr3+ and Ni2+ ions. Additionally, DFT calculations identify specific site occupations, which favor unidirectional ET from Cr3+ to Ni2+ ions. As a result, the significant absorption of excitation light by heavy‐doping Cr3+ ions and high radiative transition probability in Ni2+ ions synergistically result in a record high EQE. These findings provide pioneering insight into rational NIR‐II light generation by deliberated control of ET pathway in heavily doped systems, thereby with promising implications for NIR spectroscopy applications. [ABSTRACT FROM AUTHOR]

NIR‐II luminescent materials are the key enablers of smart spectroscopy‐based techniques, offering capabilities for nondestructive analysis and bio‐imaging. Here, a broadband NIR‐II luminescence with a recorded external quantum efficiency (EQE) of 76% in LiGa5O8 are demonstrated, using heavily doping Cr3+ ion (10%) as a light harvester and a controllable energy transfer (ET) from Cr3+ to Ni2+ (0.4%) ions. Even though the Cr3+ ion produces substantially weak luminescence due to concentration quenching, the introduction of Ni2+ ions effectively extract the excitation energy to generate NIR‐II luminescence. Complementary investigations using synchrotron‐based EXAFS fittings and structural refinement disclose a significant structural distortion in the LiGa5O8 compound, which facilitates the relaxation of the parity‐selection rules for Cr3+ and Ni2+ ions. Additionally, DFT calculations identify specific site occupations, which favor unidirectional ET from Cr3+ to Ni2+ ions. As a result, the significant absorption of excitation light by heavy‐doping Cr3+ ions and high radiative transition probability in Ni2+ ions synergistically result in a record high EQE. These findings provide pioneering insight into rational NIR‐II light generation by deliberated control of ET pathway in heavily doped systems, thereby with promising implications for NIR spectroscopy applications. [ABSTRACT FROM AUTHOR]

A series of Lu 2(1- x) Tb 2 x (WO 4) 3 (x = 0.00–1.00) white powder materials were prepared by a high-temperature solid-phase method. The crystal structure, microscopic morphology, elemental composition, bandgap energy, photoluminescence properties, and thermal stability of luminescence of the prepared materials were analyzed and studied through room and high temperature X-ray diffraction patterns, field emission scanning electron microscopy images, energy energy-dispersive spectra and X-ray photoelectron spectra, diffuse reflectance spectra, room and high temperature photoluminescence spectra. Under 260 nm excitation, the green emitting Lu 2(1- x) Tb 2 x (WO 4) 3 samples exhibited an optimum Tb3+ doping concentration at x = 0.30. Calculated results illustrate that the concentration quenching was mainly caused by dipole-dipole interaction. Lu 1.98 Tb 0.02 (WO 4) 3 phosphor exhibited thermally enhanced luminescence at 120 °C, with a maximum luminescence intensity of 254 % of the initial room temperature intensity. Lu 1.4 Tb 0.6 (WO 4) 3 phosphor exhibited thermally enhanced luminescence at 150 °C, with a maximum luminescence intensity of 109 % of the initial room temperature intensity. The mechanism of the thermally enhanced luminescence phenomenon is further discussed to be the adsorbed crystal water and the negative thermal expansion of the material. Thermally enhanced luminescence is of great significance in overcoming luminescent thermal quenching phenomenon, improving the luminescence efficiency, optimizing the material design, and so forth. It has potential applications in high-temperature lighting, display technology, temperature sensing, and optical anti-counterfeiting. [ABSTRACT FROM AUTHOR]

Li2-3xLnxGeTeO6 phosphors with doping of Ln3+ (Ln = Eu3+,Tb3+:0.0 < x < 0.1) were successfully prepared. Parent Li2GeTeO6 was obtained by the solid-state method, while Ln-doped compositions were synthesized by the facile ion-exchange method. The prepared phosphors were characterized by powder x-ray diffraction (P-XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy techniques. All of the samples were crystallized in rhombohedral structure with space group R3/(146). The photoluminescence (PL) and thermoluminescence (TL) characteristics of Li2-3xLnx3+GeTeO6 were studied. The excitation spectra of Eu3+/Tb3+-doped samples were obtained by monitoring the 611/544 nm emission line. The emission spectra of Eu3+/Tb3+-doped samples were recorded by excitation at 394/372 nm. The Li2-3xEuxGeTeO6 phosphor exhibited red emission with a maximum intense band at 611 nm. The Li2-3xTbxGeTeO6 phosphor gave a strong emission band at 544 nm in the green range. The variation in emission with dopant concentration was studied. It was found that the concentration quenching was predominant above 0.05 mol.% in both Eu3+- and Tb3+-doped phosphors, which was demonstrated based on Blasse's equation and Dexter's theory. The chromaticity coordinates of Eu3+- and Tb3+-incorporated phosphors were located at red and green regions, respectively, as per NTSC standards. The colour purity values for 0.05 mol.% of Eu3+ (Tb3+)-doped Li2GeTeO6were 54% and 43%, respectively. The correlated colour temperature (CCT) values of Li2-3xEuxGeTeO6and Li2-3xTbxGeTeO6 were 2763 K and 4562 K, respectively, indicating their suitability for use in warm and cool white-light devices. The parameters of trap-depth/activation-energy, order of kinematics and frequency-factor of the synthesized samples were calculated using the Chen glow curve peak-shape method. The investigation shows Eu3+- and Tb3+-doped Li2GeTeO6 compositions can be utilized as white-LEDs. [ABSTRACT FROM AUTHOR]

A series of Tb3+, Li+ co-doped ZnO phosphors were prepared using a precipitation method. X-ray diffraction (XRD) analysis indicated the successful incorporation of Tb3+ into the ZnO lattice. The influence of Tb3+ doping content and Li+ charge compensator on the photoluminescence (PL) properties of ZnO:Tb3+ was investigated. Under UV excitation, emissions corresponding to electron transitions 5D 4 →7F J (J = 0,1,2,3,4,5,6) were observed from Tb3+ ions, including an unusual emission transition at 673 nm, which significantly enriches our understanding of Tb3+ luminescence. The critical concentration quenching of Tb3+ in ZnO:Tb3+ occurs at 7 mol%, as explained by the Van Uitert equation, which attributes this phenomenon to dipole-dipole interactions. Surprisingly, incorporating Li+ for charge balancing led to a reduction in the luminescence intensity of ZnO:7 mol%Tb3+, x%Li+ phosphors (x = 0.01 and 0.07) at 544 nm. This reduction highlights an increased degree of lattice distortion due to Li⁺ inclusion. Furthermore, CIE chromaticity analysis showed that the optimal doping concentration of 0.07 Tb³⁺ shifted the color coordinates towards vivid green, with a color temperature of approximately 6241 K, indicating of neutral white light. [ABSTRACT FROM AUTHOR]

A yellowish‐green emitting phosphor Ba3YAl2O7.5:Eu2+ was synthesized by a solid‐state method. The crystal structure, luminescence, concentration quenching, fluorescence decay, and thermal quenching properties were systematically investigated. Under blue light (440 nm) excitation, Ba3YAl2O7.5:Eu2+ phosphors exhibit a yellowish‐green emission peaking at 550 nm with a full width at half maximum ∼ 69 nm, and The Commission Internationale de l'Eclairage (CIE) coordinates of Ba3YAl2O7.5:Eu2+ are (0.4064, 0.5811). Structural analysis and Van Uitert equation along with fluorescence lifetime analysis reveal that Eu2+ ions occupy 6‐coordinated Y and 9‐coordinated Ba sites in Ba3YAl2O7.5, and therefore generate two emission sub‐bands at 582 and 548 nm. In addition, Ba3YAl2O7.5:Eu2+ phosphor remaining 43% photoluminescence emission intensity at 125°C with an activation energy of 0.372 eV. Utilizing the title phosphor (Ba3YAl2O7.5:3%Eu2+), commercial red (Ca,Sr)AlSiN3:Eu2+ (CSAlSi:Eu2+) phosphor, and InGaN‐based blue light emitting diode (LED) chip, a proof‐of‐concept warm white LEDs (WLEDs) with a color rendering index of 80.1, CIE chromaticity coordinates of (0.411, 0.381), luminous efficacy of ∼ 22.13 lm/W, and correlated color temperature of ∼ 3288 K is achieved. Thus, Eu2+ activated Ba3YAl2O7.5 phosphors have the potential application in WLEDs pumped by a blue LED chip for solid‐state lighting application. [ABSTRACT FROM AUTHOR]

A yellowish‐green emitting phosphor Ba3YAl2O7.5:Eu2+ was synthesized by a solid‐state method. The crystal structure, luminescence, concentration quenching, fluorescence decay, and thermal quenching properties were systematically investigated. Under blue light (440 nm) excitation, Ba3YAl2O7.5:Eu2+ phosphors exhibit a yellowish‐green emission peaking at 550 nm with a full width at half maximum ∼ 69 nm, and The Commission Internationale de l'Eclairage (CIE) coordinates of Ba3YAl2O7.5:Eu2+ are (0.4064, 0.5811). Structural analysis and Van Uitert equation along with fluorescence lifetime analysis reveal that Eu2+ ions occupy 6‐coordinated Y and 9‐coordinated Ba sites in Ba3YAl2O7.5, and therefore generate two emission sub‐bands at 582 and 548 nm. In addition, Ba3YAl2O7.5:Eu2+ phosphor remaining 43% photoluminescence emission intensity at 125°C with an activation energy of 0.372 eV. Utilizing the title phosphor (Ba3YAl2O7.5:3%Eu2+), commercial red (Ca,Sr)AlSiN3:Eu2+ (CSAlSi:Eu2+) phosphor, and InGaN‐based blue light emitting diode (LED) chip, a proof‐of‐concept warm white LEDs (WLEDs) with a color rendering index of 80.1, CIE chromaticity coordinates of (0.411, 0.381), luminous efficacy of ∼ 22.13 lm/W, and correlated color temperature of ∼ 3288 K is achieved. Thus, Eu2+ activated Ba3YAl2O7.5 phosphors have the potential application in WLEDs pumped by a blue LED chip for solid‐state lighting application. [ABSTRACT FROM AUTHOR]

ABSTRACTMicrospheres composed of Y-containing materials are effective agents for cancer radioembolization therapy using β-rays. The distribution and dynamics of these microspheres in tissues can be easily determined by providing the microspheres with an imaging function. In addition, the use of quantum dots will enable the detection of microspheres at the individual particle level with high sensitivity. In this study, core – shell quantum dots were bound to chemically modified yttria microspheres under various conditions, and the effect of reaction conditions on the photoluminescence properties of the microspheres was investigated. The quantum dots were immobilized on the surfaces of the microspheres through dehydration – condensation reactions between the carboxy groups of quantum dots and the amino groups of silane-treated microspheres. As the reaction time increased, the photoluminescence peak blue shifted, and the photoluminescence intensity and lifetime decreased. Therefore, a moderate period of the immobilization process was optimal for imparting effective photoluminescence properties. This study is expected to facilitate particle-level tracking of microsphere dynamics in biological tissues for the development of minimally invasive cancer radiotherapy of deep-seated tumors.

The disadvantage of chalcogenide glasses containing rare earth ions as luminescent materials for the IR optical range is the strong concentration quenching of luminescence due to the non-uniform distribution of rare earth ions in the glass matrix. This study investigates the effect of grinding chalcogenide glass containing Pr3+ ions in a planetary ball mill on its luminescent properties in the near-IR range, as well as its optical properties and structure. The results indicate that milling, under certain conditions, leads to a decrease in the concentration quenching of the luminescence of Pr3+ ions. This finding suggests that milling can be used in the development of glassy materials with the increased efficiency of luminescence of rare earth ions. However, it is essential to consider that high-energy milling may result in the formation of areas with increased pressure in the obtained material, leading to structural changes in the glass.

The disadvantage of chalcogenide glasses containing rare earth ions as luminescent materials for the IR optical range is the strong concentration quenching of luminescence due to the non-uniform distribution of rare earth ions in the glass matrix. This study investigates the effect of grinding chalcogenide glass containing Pr3+ ions in a planetary ball mill on its luminescent properties in the near-IR range, as well as its optical properties and structure. The results indicate that milling, under certain conditions, leads to a decrease in the concentration quenching of the luminescence of Pr3+ ions. This finding suggests that milling can be used in the development of glassy materials with the increased efficiency of luminescence of rare earth ions. However, it is essential to consider that high-energy milling may result in the formation of areas with increased pressure in the obtained material, leading to structural changes in the glass. [ABSTRACT FROM AUTHOR]

Luminescence quench is common in overdoped upconversion nanoparticles. Various methods have been proposed to counteract the adverse effects of concentration quenching on luminescence, but in upconversion nanoparticles that are highly doped with both sensitizers and activators, the factors that contribute to the diminishing of the emission cannot be summarized by a single cause. Herein, a core-shell design is used to spatially separate the sensitizer (Yb3+) and activator (Er3+) and to modulate the emission by changes in the distribution position as well as the concentration of the dopant ions in order to probe the factors affecting the luminescence. When the sensitizer ions are located in the core, the luminescence intensity of the nanoparticles is significantly weaker than that of the other distribution, which implies that the effect of sensitizer and activator on luminescence in the highly doped state has a different and more complex mechanism. The intensity of the emission is more affected by Yb3+ than Er3+, which includes not only the self-quenching of Yb3+, but also the dominance in the Yb3+–Er3+ cross-relaxation. In this finding may provide new ideas for revealing the reasons for the diminished luminescence of highly doped upconversion nanoparticles and thus for enhancing luminescence. [ABSTRACT FROM AUTHOR]

Structural, optical and photoluminescent properties of La2−xPrx(MoO4)3 phosphors with different doping concentrations of Pr3+, synthesized by conventional solid-state and solution combustion routes were studied. X-ray diffraction studies of compounds synthesized through conventional solid-state ceramic route confirm that all samples crystallized in monoclinic La2(MoO4)3 structure with c2/c space group, while combustion synthesized compounds show the existence of two different crystal environments. Analysis of UV–visible diffuse reflectance spectra (DRS) shows characteristics of absorption bands in blue and red regions for Pr3+ substituted La2(MoO4)3 samples, synthesized by both methods. The calculated band gap from the DR spectrum showed an inverse dependence with Pr3+ doping concentration for solid-state synthesized La2−xPrx(MoO4)3 samples, while for combustion synthesized La2−xPrx(MoO4)3 compounds the variation of band gap with concentration is not monotonous. The photoluminescence emission spectrum of blue excited La2−xPrx(MoO4)3 phosphors synthesized by both routes showed similar multicoloured emission bands. Maximum emission intensity was observed for Pr3+ concentration of x = 0.05 in both synthesis methods. The exchange interaction between nearest activator ions leads to concentration quenching of luminescence for solid-state synthesized La2−xPrx(MoO4)3 compounds and dipole–dipole interaction for combustion synthesized La2−xPrx(MoO4)3 compounds. The average emission colour of the blue excited La2−xPrx(MoO4)3 phosphors lies in the yellow–orange region. The CCT values lie in the warm light region and the luminescence lifetime of 8 µs for red emission peak showed promising applications requiring fast switching response. [ABSTRACT FROM AUTHOR]

A strong green emission is detected in a Tb3+-activated Ca9Bi(VO4)7 nanocrystals manufactured via the sol–gel route. Trigonal crystal prototypes with the R3c (161) space group were fabricated with unevenly shaped particles with a 41–64 nm diameter. When excited by UV radiation, the photoluminescence band exhibits a strong green-light generation at wavenumbers 18281 cm−1, which is believed to be due to the 5D4 → 7F5 transition. The various energy transmission phenomena such as radiative lifetime, quantum efficiency, and non-radiative energy losses are also discussed for the synthesized nanophosphor when excited by UV radiation. The maximum observed luminescence intensity was obtained with 5.0 mol% Tb3+ doping when excited at 283 nm. There is a concentration quenching effect owing to the d–d exchanges. The CIE coordinates lie in the greenish domain of the chromaticity chart with a CCT value of 5937 K, thus approving their compatibility in LED fabrication for indoor lighting applications. [ABSTRACT FROM AUTHOR]

In this article, we present the synthesis and characterization of Eu3+-activated KMLS:Eu3+ phosphor for pc-WLEDs, latent fingerprint detection, and security ink applications. The structural phase, luminescent property, and colour purity of the as-prepared phosphor were investigated. XRD profiles and Rietveld refinement analysis confirm the hexagonal crystal system of the as-prepared phosphor. Concentration quenching effect was not observed up to 17 mol% of Eu3+. The site occupancy preferences of Eu3+ were investigated using the bond-valence model. The CIE-coordinate of optimal Eu3+ is estimated to be close to the standard NTSC value, and color purity is found to be above 90% for all the Eu3+ concentrations. Both Judd-Ofelt (J-O) analysis and asymmetric ratios revealed that the local environment around Eu3+ is asymmetric in nature. The radiative properties, including the stimulated emission cross section and optical gain parameters, of the highest concentration of Eu3+ (17mol%) were determined. Further, the results of thermal quenching analysis show that 91% of the luminescence intensity can be maintained at 150 °C, demonstrating good thermal stability. The multilevel ridge characteristics of the latent fingerprint stained with as-prepared phosphor could be clearly visualized under 254 nm UV excitation. All of the above results indicate that as-prepared phosphor materials can be suitable for use in forensic applications as well as solid state lighting applications. [ABSTRACT FROM AUTHOR]

A perovskite material, Barium Zirconate (BZO) doped with 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0 mol% of Europium (III) were prepared using a solid-state reaction technique. X-ray diffraction (XRD) pattern of BZO doped with 2.0 mol% of Europium was observed. The experimental XRD pattern matched significantly with the standard XRD pattern with the Crystallographic Open Database (COD) card number (96-153-2744) with a figure of merit of 0.89. Photoluminescence emission spectra of the samples prepared exhibited two prominent peaks centred at 592 nm and 612 nm which were attributed to the transitions (5D0→7F2) and (5D0→7F4) respectively. The concentration quenching occurred when the doping concentration was increased after 2.0 mol% of Europium (III). A coordinate (0.58, 0.41) was found in the Colour Chromaticity Diagram (CIE), which falls in orange–red region. The method involved in the calculation of the Judd-Ofelt intensity parameter was briefly described. The ratio R21 = I (5D0→7F2)/I (5D0→7F1) was found as 2.93 which is indicative that the electric dipole transitions are more prominent in comparison to the magnetic dipole transitions. The value of intensity parameters Ω 2 Ω 4 was found as 4.98 × 10−20 cm2 and 8.56 × 10−20 cm2 respectively. [ABSTRACT FROM AUTHOR]

A series of Eu3+ doped Sr2GdTaO6 (SGT) phosphors with double perovskite structure were synthesized via a high-temperature solid-state reaction approach. The crystal structure, morphology and luminescence properties were characterized by means of X-ray diffraction, transmission electron microscope, luminescence spectroscopy and fluorescence decay lifetimes, respectively. Under the excitation of 394 nm, intense red emission in the visible region was observed in Eu3+ doped SGT phosphors, and the critical quenching concentration of Eu3+ in SGT phosphors was derived to be 15 mol%. The chromaticity coordinates and color purity of SGT: 15 mol% Eu3+ were calculated to be (0.61, 0.36) an 93.82 %, respectively. Meanwhile, it was also confirmed that the electric quadrupole–quadrupole interaction is responsible for the luminescence concentration quenching of Eu3+. The internal quantum efficiency of SGT: Eu3+ phosphors with different Eu3+ concentrations were calculated. Furthermore, the crossover process was confirmed to be the main mechanism for luminescence thermal quenching based on the temperature-dependent emission spectra and temperature-dependent fluorescence lifetimes. In addition, the Judd-Ofelt parameters, radiative transition rates and branch ratios from the 5D0 emitting states to various lower energy states were evaluated with the aid of the Judd-Ofelt theory, respectively. All results indicate that SGT: Eu3+ samples are a promising red-emitting phosphor.

Silicon-substituted apatite doped with Dy3+ ions was obtained by using microwave assisted hydrothermal techniques. The general formula of obtained samples is related to Ca 10-x Dy x (PO 4) 2 (SiO 4) 4 F 2 , where x = 0.05; 0.1; 0.2; 0.5. The structural, and morphological features of the obtained materials were determined by using XRD (X-ray powder diffraction) and SEM imaging (Scanning Electron Microscopy). The Rietveld refitment was used for estimation of unit-cell parameters. The photoluminescence of the Dy3+ ions was detected and analysed as a function of dopant concentration. The particular attention was focused on the concentration quenching of Dy3+ ion luminescence as well as the critical transfer radius was calculated. The chromaticity diagram, emission colour and correlated colour temperature (CCT) were evaluated. [ABSTRACT FROM AUTHOR]

Luminescence quenching at high dopant concentration and temperature typically limits the brightness of luminescence materials, which remains a major obstacle in diverse technological applications, especially in the field of luminescence thermometry. In this work, a unique class of non‐concentration quenching double‐tungstate phosphors is reported that feature the near‐unity quantum yield of Tb3+ and Eu3+ emissions induced by the structural confinement effect. Mechanistic studies affirm that the activator ions can be isolated in NaYW2O8 crystal to confine the absorbed photon energy, leading to a relatively high quenching concentration of various lanthanide activators. By facilitating interionic cross‐relaxation at heavy dopant concentration, a remarkable thermal enhancement of Tb3+ emissions over 20‐fold upon the excitation of excited‐state absorption is recorded. In contrast, thermally quenched emissions are detected under the excitation of ground‐state absorption. This excitation wavelength‐dependent thermal behavior of Tb3+ emissions is harnessed for single‐band ratiometric thermometry, registering superior thermal sensitivity and resolution (Sr = 4.01% K−1, δT = 0.1 K). The advances in combating concentration and thermal quenching of luminescence materials provide exciting opportunities for flexible thermometry in real‐world sensing scenarios. [ABSTRACT FROM AUTHOR]

In the present work, a series of Li2SiO3 phosphors activated with the different concentrations of xEu3+ ions have been synthesized by solid-state reaction method. First, the concentration of Eu3+ ions and firing temperature was optimized. The orthorhombic crystal structure of the prepared compound was confirmed by the powder X-ray diffractometry (PXRD) technique. Under the excitation of 394 nm, the emission spectra of xEu3+ ions show the characteristic emission peaks assigned to transitions of the 5D0 → 7Fj (J = 0, 1, 2, 3, 4), which emits an intense orange–red light peaked at 617 nm. Concentration quenching occurs when the Eu3+ concentration is beyond 0.04 mol. The Eu3+ concentration quenching mechanism was verified to be multipole–multipole interaction and the critical transfer distance (RC) is calculated to be about 14.13 Å. Commission International Eclairage (CIE), color rendering index (CRI), color correlated temperature (CCT), color purity (CP), and quantum efficiency (QE) have been calculated for each sample and were found well within the defined acceptable range. This result indicates that prepared phosphors emitted in the orange–red region that may be useful in various solid-state lighting. [ABSTRACT FROM AUTHOR]

Heat-resistant polymers with an intense, visible photoluminescence (PL) functionality are presented. A polybenzoxazole (PBO) containing hexafluoroisopropylidene (HFIP) side groups exhibited an intense purple PL with a quantum yield, ΦPL, of 0.22 (22%), owing to the effectively disturbed concentration quenching (CQ) in the fluorophore units by the bulky HFIP side groups. The chain ends of a wholly cycloaliphatic polyimide (PI), derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4′-methylenebis(cyclohexylamine) (MBCHA), were modified with conjugated monoamines. The PI derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (2,3,6,7-NTDA) and MBCHA exhibited a very high glass transition temperature (Tg = 376 °C) and purple fluorescence from the S1(π,π*) state. However, its ΦPL value was lower than expected. A pronounced effect of fluorophore dilution using CBDA on the PL enhancement was observed. This is closely related to the planar structure of the 2,3,6,7-NTDA-based diimide units. By contrast, the counterpart using an 2,3,6,7-NTDA isomer, 1,4,5,8-NTDA, was virtually non-fluorescent, despite its sufficient dilution using CBDA. The PI film obtained using 3,3″,4,4″-p-terphenyltetracarboxylic dianhydride (TPDA) with a non-coplanar structure and MBCHA exhibited an intense blue fluorescence spectrum (ΦPL = 0.26) peaking at 434 nm. The dilution approach using CBDA enhanced its fluorescence up to a high ΦPL value of 0.41. Even when TPDA was combined with an aromatic diamine, 2,2′-bis(trifluoromethyl)benzidine (TFMB), the intense blue fluorescence was observed without charge-transfer fluorescence. A semi-cycloaliphatic PI derived from TFMB and a novel cycloaliphatic tetracarboxylic dianhydride, which was obtained from a hydrogenated trimellitic anhydride derivative and 4,4′-biphenol, was used as another host polymer for 9,10-bis(4-aminophenyl)anthracene (BAPA). The BAPA-incorporating PI film resulted in a significant PL enhancement with a considerably high ΦPL of 0.48. This PI film also had a relatively high Tg (265 °C). A reactive dye, N,N′-bis[4-(4-amino-3-methylbenzyl)-2-methylphenyl]-3,4,9,10-perylenetetracarboxydiimide, was harnessed as a fluorescence probe to explore transamidation between polyimide precursors in solution.

Highly crystalline and single phase BaGd 2 − x Dy x O 4 (0.00 ≤ x ≤ 0.16) phosphors, with an average crystallite size around 126 nm, have been synthesised using solid-state reaction technique. The structural and optical properties of these phosphors have been studied in detail to establish an unambiguous correlation between these properties. High-angle annular dark field (HAADF) images have confirmed that the constituent elements are homogeneously distributed in the particles, and their elemental composition has been established using X-ray photoelectron spectroscopy (XPS). The tuning of optical band gap with x has been achieved, which is a rare achievement in these phosphors. Also, the optimum concentration of Dy 3 + ions has been found to be 0.8 mol%, which is the lowest among the Dy 3 + doped BaGd 2 O 4 phosphors reported so far. This concentration quenching effect has been discussed on the basis of a combination of decay curve analysis, calculation of average critical distance between the Dy 3 + ions and integrated intensities of photoluminescence (PL) emission bands. The average crystallite size and optical band gap has also been found to decrease after x = 0.016, from which their correlation with concentration quenching effect has been investigated. The asymmetry ratio between the integrated intensities of yellow and blue PL emission bands has been observed to be greater than 2 throughout x , which confirmed the preferential lattice site for Dy 3 + ions in these phosphors with present synthesis conditions. The variation of asymmetry ratio and Gd 3 + -dominated IR-active lattice vibrations with x , and Vegard's law pertaining to the volume of a unit cell confirms that the local bonding environment in the lattice of these phosphors gets modified at x = 0.016. The photometric parameters for these phosphors reveal their suitability for fabrication of warm light orange LEDs on appropriate UV chips. [ABSTRACT FROM AUTHOR]

Magnetic‐luminescent composite nanoparticles (Fe3O4@ZnO:RE) with a core/shell structure are produced by a simple process. Magnetite nanoparticles (Fe3O4) are coated with rare‐earth‐doped zinc oxide (ZnO). Core/shell structure is confirmed by high‐resolution transmission electron microscopy (HR‐TEM) analysis. X‐ray diffraction analysis results show that cubic magnetite Fe3O4 and hexagonal ZnO phases originate from the core and the shell, respectively. Hexagonal ZnO and cubic magnetite Fe3O4 phases belonging all nanoparticles are confirmed by HR‐TEM benefiting the lattice fringe. All the nanoparticles present superparamagnetic behavior. Under 532 nm excitation, they release the emission in the visible and infrared regions. They exhibit blue–green emission attributed to 2H11/2–4I15/2, 4S3/2–4I15/2 transitions, red emission attributed to 4F9/2–4I15/2 transitions, and infrared emission ascribed to 4F9/2–4I15/2, 2F7/2–2F5/2 transitions. Above the 0.2mol% dopant ratio, the luminescence intensity starts to decrease because of the concentration quenching. The produced nanoparticles are promising for bioimaging and magnetic hyperthermia treatment, due to their magnetic and luminescent properties, orientation to the target area, and their presence in the target area can be determined. [ABSTRACT FROM AUTHOR]

GdAl 3 (BO 3) 4 :Dy3+, Sm3+, Eu3+, and Tb3+ samples were successfully achieved via a sol-gel combustion method. The observed XRD analysis confirms the formation of the desired GAB host, indicating rhombohedral structures that agree well with JPCD card number 72–1985. The FTIR analyses show the detection of B − O stretching and B − O − B bending modes as well as Al − O and Gd − O bonds in the phosphor samples. Energy dispersive spectroscopy (EDS) analysis reveals that Sm, Eu, Dy, and Tb have been successfully doped into GdAl 3 (BO 3) 4. The observed broad intrinsic luminescence band can be caused by oxygen-induced luminescence defects in the GAB host with hydrous precursors. The luminescence properties of rare earth ion-doped GdAl 3 (BO 3) 4 samples are analysed by photoluminescence spectra, showing their optimal doping concentrations and critical distances of Dy3+, Eu3+, Sm3+ and Tb3+ are 2 wt% − 25.8 Å, 7 wt% − 17 Å, 1 wt% − 32.59 Å, and 7 wt% − 17.03 Å. Additionally, the energy transfer mechanism for luminescence quenching was determined as dipole-dipole (for Dy3+, Eu3+, and Tb3+) or dipole-quadrupole (for Sm3+) and the cross-relaxation process. GdAl 3 (BO 3) 4 samples obtained by doping with different RE3+ ions exhibit intense light emissions with different colors originating from different RE3+ ions under 349 nm excitation. When doped with different concentrations of RE3+ ions, the luminescence properties of the samples changed. The synthesized luminescence materials have potential applications in lighting and display technologies. [ABSTRACT FROM AUTHOR]

In this work, Lanthanum oxychloride LaOCl: Eu3+ (0–9 mol%) was synthesized using a conventional solid-state approach over the course of relatively low temperature (400 °C) and a shorter duration of 1 h. To investigate the phase purity of phosphors, crystallographic studies were performed using PXRD, which revealed the tetragonal structure with space group P4/nmm (No. 129). Morphological investigations were made using FESEM which unveils the agglomeration of phosphors. Photoluminescence spectra reveals that, the intensity of the 5D 0 →7F 2 transition (618 nm), which increases with an increase in Eu3+ concentration (1–9 mol%), rises to a maximum of 7 mol% before quenching causes it to fall. The reason behind the quenching concentration of Eu3+ ions at 7 mol% was dipole-quadruple interaction which is determined using the Van Uitert equation. To improve luminescence efficiency metal ions like Li+, Na+, K+, Ca2+, and Bi3+ were exploited, among these LaOCl: Eu3+ co-doped with Li+ ion exhibit the highest PL intensity (39 times that of Eu3+). The Commission International de I'Eclairage (CIE) chromaticity coordinates of LaOCl: Eu3+ co-doped with Li+ phosphor is (0.590, 0.346) which is close to commercial red light-emitting phosphors. These phosphor materials were mixed with PVA and developed a flexible phosphor polymer composite, which can be used for flexible display device applications. Spectral parameters like J-O intensity parameters are used to analyze optical materials, these parameters were determined with the help of luminescence spectra. [ABSTRACT FROM AUTHOR]

This work demonstrates a multi‐tiered computational workflow to accurately and efficiently investigate the electronic properties of OLED materials in realistic thin‐film morphologies. We apply a range of robust atomistic‐scale modeling and simulation methods to reveal hybrid electronic states in OLED films. This work paves the way for efficient materials screening before laborious synthesis and device fabrication. [ABSTRACT FROM AUTHOR]

Heat-resistant polymers with an intense, visible photoluminescence (PL) functionality are presented. A polybenzoxazole (PBO) containing hexafluoroisopropylidene (HFIP) side groups exhibited an intense purple PL with a quantum yield, ΦPL, of 0.22 (22%), owing to the effectively disturbed concentration quenching (CQ) in the fluorophore units by the bulky HFIP side groups. The chain ends of a wholly cycloaliphatic polyimide (PI), derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) and 4,4′-methylenebis(cyclohexylamine) (MBCHA), were modified with conjugated monoamines. The PI derived from 2,3,6,7-naphthalenetetracarboxylic dianhydride (2,3,6,7-NTDA) and MBCHA exhibited a very high glass transition temperature (Tg = 376 °C) and purple fluorescence from the S1(π,π*) state. However, its ΦPL value was lower than expected. A pronounced effect of fluorophore dilution using CBDA on the PL enhancement was observed. This is closely related to the planar structure of the 2,3,6,7-NTDA-based diimide units. By contrast, the counterpart using an 2,3,6,7-NTDA isomer, 1,4,5,8-NTDA, was virtually non-fluorescent, despite its sufficient dilution using CBDA. The PI film obtained using 3,3″,4,4″-p-terphenyltetracarboxylic dianhydride (TPDA) with a non-coplanar structure and MBCHA exhibited an intense blue fluorescence spectrum (ΦPL = 0.26) peaking at 434 nm. The dilution approach using CBDA enhanced its fluorescence up to a high ΦPL value of 0.41. Even when TPDA was combined with an aromatic diamine, 2,2′-bis(trifluoromethyl)benzidine (TFMB), the intense blue fluorescence was observed without charge-transfer fluorescence. A semi-cycloaliphatic PI derived from TFMB and a novel cycloaliphatic tetracarboxylic dianhydride, which was obtained from a hydrogenated trimellitic anhydride derivative and 4,4′-biphenol, was used as another host polymer for 9,10-bis(4-aminophenyl)anthracene (BAPA). The BAPA-incorporating PI film resulted in a significant PL enhancement with a considerably high ΦPL of 0.48. This PI film also had a relatively high Tg (265 °C). A reactive dye, N,N′-bis[4-(4-amino-3-methylbenzyl)-2-methylphenyl]-3,4,9,10-perylenetetracarboxydiimide, was harnessed as a fluorescence probe to explore transamidation between polyimide precursors in solution. [ABSTRACT FROM AUTHOR]

A series of strontium stannate (SrSnO 3) doped with Dy3+ ions at various wt % concentrations (1, 2, 3 and 5) were synthesized via hydrothermal reaction and analysed using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), environmental electron scanning microscope (ESEM), photoluminescence (PL) and, cathodoluminescence (CL). The XRD results confirmed that all samples were assigned to cubic perovskite-type SrSnO 3 structured with the P m 3 m ‾ space group. The PL emission spectrum of Dy3+ activated samples consisted of some characteristic peaks located at 481 nm, 572 nm, 660 nm and 753 nm, corresponding to (4F 9/2 → 6H 15/2 , blue), (4F 9/2 → 6H 13/2 , yellow), 660 nm (4F 9/2 → 6H 11/2 , red) and 753 nm (4F 9/2 → 6H 9/2 , red) transitions. The PL emission line intensity is gradually enhanced with an increase in doping concentration up to 3 wt %, followed by concentration quenching. The confinement effects of localized resonant energy transfer might cause higher concentration quenching. PL emission spectra were affected by the temperature range from 10 K to 300 K. PL emission anomalies at 270 K in SrSnO 3 :Dy3+ have been reported to be consistent with a structural phase transition at this temperature. This work confirms Singh et al.'s observation, revealing that SrSnO 3 has a phase transition at 270 K. [ABSTRACT FROM AUTHOR]

Rare-earth element-free fluorescent materials are eco-friendlier than other traditional fluorescent precursors, such as quantum dots and phosphors. In this study, we explore a simple and facile solution-based technique to prepare fluorescent films, which are highly stable under ordinary room conditions and show hydrophobic behaviour. The proposed hybrid material was designed with hybrid composites that use polyvinyl butyral (PVB) as a host doped with organic dyes. The red and green fluorescent films exhibited quantum yields of 89% and 80%, respectively, and both are very uniform in thickness and water resistant. Additionally, PVB was further compared with another polymeric host, such as polyvinylpyrrolidone (PVP), to evaluate their binding ability and encapsulation behaviour. Next, the effect of PVB on the optical and chemical properties of the fluorescent materials was studied using UV spectroscopy and Fourier transform infrared spectroscopy. The analysis revealed that no new bond was formed between the host material and fluorescent precursor during the process, with intermolecular forces being present between different molecules. Moreover, the thickness of the fluorescent film and quantum yield relation were evaluated. Finally, the hydrophobic nature, strong binding ability, and optical enhancement by PVB provide a powerful tool for fabricating a highly efficient fluorescent film with enhanced stability in an external environment based on its promising encapsulation properties. These efficient fluorescent films have a bright potential in colour conversion for next-generation display applications. [ABSTRACT FROM AUTHOR]

Multifunctional green emitting (Potassium Calcium Fluoride: x Trivalent Terbium) KCaF 3 : xTb3+ (x = 0.01, 0.03, 0.05, 0.07, 0.09, and 0.11 mol%) phosphor was synthesized by solid state reaction method. Crystal structure, morphology, photoluminescence and thermoluminescence properties were investigated in detail. Photoluminescence emission spectrum showed the characteristic maximum intensity peak at 543 nm corresponding to Tb3+ emission band when excited using an UV light of wavelength 374 nm. The concentration quenching effect of Tb3+ in KCaF 3 phosphor was caused by dipole – quadrupole interaction between Tb3+ ions. CIE coordinates of KCaF 3 : xTb3+ (x = 0.05 mol%) was found to be x = 0.2959 and y = 0.6592 positioning at green region. Beta irradiated thermoluminescence glow curve was recorded on KCaF 3 : xTb3+ (x = 0.05 mol%) phosphor. Low temperature signals in TL glow curve were removed using bleaching or preheating technique. The optimization of preheat temperature was performed using different temperature and found 125 °C (peak 1) and 210 °C (peak 2) as an optimized temperature. Temperature of maximum TL intensity (T m) of peak 1 and peak 2 was found to be 181 °C and 292 °C, respectively. The activation energy (E a) and frequency factor (s) of peak 1 and peak 2 were calculated using peak shape method and variable heating rate method (VHR). Characteristic studies for dosimetry application such as dose response and reusability of KCaF 3 : xTb3+ (x = 0.05 mol%) were investigated in detail. [ABSTRACT FROM AUTHOR]

A novel double perovskite BaSrYZrO 5.5 :Eu3+ red-emitting phosphor was synthesized and characterized by XRD, SEM and PL analyses. The structure of the prepared phosphor was confirmed through JCPDS as well as Rietveld refinement analysis. The present phosphor shows an intense red emission at 613 nm when excited by 394 nm. The CIE colour coordinates value of BaSrYZrO 5.5 :Eu3+ (9 mol%) phosphor is found to be (0.6181, 0.3783) and it has high colour purity of 99.1%. The 613 nm transition integrated intensity of the present phosphor is 4.44 times higher compared to the commercial red phosphor. The thermal stability and Quantum yield of optimized BSYZ:Eu3+ (9 mol%) phosphor were also calculated. The BSYZ:Eu3+ phosphor results can be employed as an efficient red component in latent fingerprint detection and anti-counterfeiting applications. • For the first time, a double perovskite BaSrYZrO 5.5 :Eu3+ red-emitting phosphor was prepared through a modified solid-state reaction method. • Increase in Eu3+ (1-11 mol%) concentration shows the reduction in CT band with the simultaneous increase in the f-f transitions intensity. • The BSYZ:Eu3+ (9mol%) red phosphor reveals 4.44 times higher integrated intensity compared to the commercial Y 2 O 3 :Eu3+ red phosphor. • BSYZ:Eu3+ red phosphor is used as a prominent candidate in latent fingerprint minutiae identification and security-ink applications. [ABSTRACT FROM AUTHOR]

Highly concentrated solutions of chlorophyll display rapid fluorescence quenching. The same devastating energy loss is not seen in photosynthetic light-harvesting antenna complexes, despite the need for chromophores to be in close proximity to facilitate energy transfer. A promising, though unconfirmed mechanism for the observed quenching is energy transfer from an excited chlorophyll monomer to a closely associated chlorophyll pair that subsequently undergoes rapid nonradiative decay to the ground state via a short-lived intermediate charge-transfer state. In this work, we make use of newly emerging fast methods in quantum chemistry to assess the feasibility of this proposed mechanism. We calculate rate constants for the initial charge separation, based on Marcus free-energy surfaces extracted from molecular dynamics simulations of solvated chlorophyll pairs, demonstrating that this pathway will compete with fluorescence (i.e., drive quenching) at experimentally measured quenching concentrations. We show that the rate of charge separation is highly sensitive to interchlorophyll distance and the relative orientations of chromophores within a quenching pair. We discuss possible solvent effects on the rate of charge separation (and consequently the degree of quenching), using the light-harvesting complex II (LH2) protein from rps. acidophila as a specific example of how this process might be controlled in a protein environment. Crucially, we reveal that the LH2 antenna protein prevents quenching, even at the high chlorophyll concentrations required for efficient energy transfer, by restricting the range of orientations that neighboring chlorophyll pairs can adopt. [ABSTRACT FROM AUTHOR]

High-temperature solid-state reaction technique was used to prepare NaY(MoO 4) 2 :Tb3+ phosphors with different Tb3+ concentrations. XRD patterns showed that the prepared samples contained only single-phased compound NaY(MoO 4) 2. The concentration-dependent green luminescent intensity of Tb3+ was studied, and it was found that the concentration quenching process is in charge of Ozawa's model. The concentration-effect of luminescence decay of 5D 4 level was explained by the Auzel's self-generated quenching theory. Starting from the Reisfeld's theory, the analysis on the luminescence decays also indicated exchange interaction was responsible for the concentration quenching. Temperature dependences of the green emission intensity and decay were comprehended based on the crossover mechanism. A novel temperature sensing technique rooting in the fluorescence dynamics of 5D 4 level of Tb3+ in NaY(MoO 4) 2 was proposed, and the absolute and relative sensitivities were deduced and assessed. [ABSTRACT FROM AUTHOR]

An innovative green emitting novel BaY1 − xTbxAl3O7 (x = 0.02, 0.03, 0.04, 0.05, and 0.06) was synthesized using urea combustion, which was a low-energy process. Using techniques such as photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM), and energy dispersive x-ray (EDX) spectroscopy, the structure and luminous properties of the phosphor were investigated. Scherrer’s equation was utilized in the XRD technique to determine the crystallite size of the suggested materials. When stimulated with the near-ultraviolet photon, PL spectra revealed intense green emission at 541 nm (5D4 → 7F5). The composition with the maximum emission intensity is BaY0.96Tb0.04Al3O7. The dipole–dipole mechanism for concentration quenching events was identified with the help of the critical energy transfer distance. The non-radiative relaxation rate (276 s− 1), radiative lifetime (0.75754 ms), and quantum efficiency (79%), of the ideal phosphor composition are calculated using Auzel’s model. The color coordinates (0.260, 0.496) align with the emission of green light. The remarkable outcomes validated the significance of the targeted nanocrystals as a superior material with prospective applications in solid-state down-converted white light-emitting diodes (WLEDs). [ABSTRACT FROM AUTHOR]

[Display omitted] • Improved luminescence of Eu3+ via energy transfer from Dy3+ doping in LAB phosphors. • Hygroscopic nature impacts PL emission through radiolysis of adsorbed water. • Controlled heating/cooling rates ensure consistent material properties. • Expanded discussion on quenching mechanisms enhances understanding. • New insights into the role of Dy3+ and Eu3+ in luminescence mechanisms. In this study, an investigation was conducted on the structural and photoluminescence (PL) characteristics of LaAl 2 B 4 O 10 (LAB) phosphors initially incorporated with Dy3+ and Eu3+ ions. Subsequently, the impact of varying Eu3+ concentration while maintaining a constant Dy3+ concentration was examined. Structural characterization was performed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDS). XRD analysis confirmed the effective embedding of both dopants into the hexagonal framework of the LAB. The PL emission spectra revealed characteristic emissions of Dy3+ (blue and yellow) and Eu3+ (red) ions. The optimized dopant concentrations of both Dy3+ and Eu3+ were observed to be 3 wt%. The dominant mechanism for concentration quenching in doped LAB phosphors was determined to be the electric dipole–dipole interaction. Co-doping with Eu3+ led to a substantial decrease in Dy3+ emission intensity (∼0.18-fold) while enhancing Eu3+ emission intensity (∼3.72-fold). The critical energy transfer distance (R C = 11.64 Å) and the analysis based on the Dexter theory confirmed that the energy transfer mechanism corresponds to dipole–dipole interaction. The color purities and correlated color temperatures (CCT) were estimated, suggesting the potential of these phosphors for warm white and red lighting applications, respectively. The observed energy transfer and luminescence properties, along with the structural and compositional characterization, highlight the promising potential of LAB:Dy3+/Eu3+ co-doped phosphors for advanced lighting and display technologies. [ABSTRACT FROM AUTHOR]

• MgTi 2 O 5 : xEu3+ phosphors are synthesized by solid-state reaction method. • Under 465 nm excitation, intense red emission was obtained at 615 nm. • Internal quantum efficiency of the phosphor was determined to be 31.65 %. • Phosphors have high color purity and warm light emission. • Synthesized red phosphor is a suitable candidate for pc-wLEDs. As one of the critical components for achieving high-quality white light emitting diodes (w-LEDs) are efficient phosphors, a series of intense red emitting Eu3+doped magnesium dititanate (Mg (1- x) Ti 2 O 5 : x Eu3+; x = 0, 0.005, 0.008, 0.01, 0.02 and 0.03 mol) phosphors were prepared via solid-state reaction method. The X-ray diffraction (XRD) patterns confirmed the phase purity and orthorhombic structure of the prepared phosphors. The Ti-O functional groups were detected from the Fourier transform infrared (FTIR) spectra and Field emission scanning electron microscopy (FESEM) images revealed agglomerated spherical-like shaped phosphor particles. Under 465 nm excitation, intense red emission corresponding to 5D 0 →7F J (J = 0, 1, 2, 3, and 4) transitions of Eu3+ ions were recorded in the photoluminescence (PL) spectra with an intense peak at 615 nm. The optimum concentration of Eu3+ ions was determined to be 1 mol% and the concentration quenching mechanism was due to the interaction between adjacent Eu3+ ions. The lifetime values of the samples were in the millisecond range and the internal quantum efficiency was determined to be 31.65 %. The Commission Internationale de l'Eclairage (CIE) coordinates of the optimum sample Mg 0.99 Ti 2 O 5 :0.01Eu3+ are (0.6421, 0.3575), lies in the red region with 99.9 % color purity and have warm correlated color temperature (CCT) values. Therefore obtained results suggest that the prepared Mg (1- x) Ti 2 O 5 : x Eu3+phosphors can be used as an efficient red phosphor for w-LED applications. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Microwave-assisted sol–gel method is used for synthesizing Eu3+-doped KYBO phosphors. • Li+ and Na+ co-doping enhances luminescence in Eu3+-doped KYBO phosphors. • Abnormal thermal stability is observed with Na+ co-doping in KYBO phosphors. • XRD and FTIR confirm structural integrity with effective dopant incorporation. • High activation energy (0.2536 eV) achieved with Na+ co-doping. Eu3+-doped and Li+/Na+ co-doped K 3 Y(BO 2) 6 (KYBO) phosphors were synthesized through a microwave-assisted sol–gel method, and their structural and photoluminescent (PL) characteristics were examined. X-ray diffraction (XRD) and Rietveld refinement confirm effective dopant incorporation and preservation of the crystalline structure. Fourier Transform Infrared (FTIR) spectroscopy indicates the maintenance of the borate structure, confirming the structural integrity of the phosphors upon doping. The addition of Li+ and Na+ co-dopants notably enhances luminescent efficiency and thermal stability, making these phosphors promising candidates for solid-state lighting (SSL) applications. PL analysis reveals strong red emission peaks at 612 nm, attributed to the 5D o → 7F 2 transition of Eu3+ ions. The study indicates that electric dipole-quadrupole interactions are the primary mechanism for energy migration, with a critical distance of approximately 22.68 Å. This mechanism contributes to concentration quenching at higher doping levels. High temperature PL measurements indicated an activation energy of 0.1389 eV for thermal quenching in the Li+ co-doped sample. Additionally, the Na+ co-doped sample exhibited an abnormal thermal stability behavior, with an even higher activation energy of 0.2536 eV. This suggests that Na+ co-doping significantly enhances the thermal resilience of the phosphor, making it more suitable for high-power light-emitting applications that operate under extreme conditions. CIE chromaticity diagrams highlight the potential for optimizing Eu3+ doping levels, combined with Li+ and Na+ co-doping, to improve luminescent performance and thermal stability for advanced SSL applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nanocrystalline LaPO 4 : Dy3+, Na+, Bi3+ was prepared using citrate based hydrothermal method and the structural characterisation was confirmed using XRD. • The photoluminescence and CIE chromaticity analysis corroborates the potential utility of the prepared sample for cool white light emission under near UV excitation and warm white light emission under blue LED excitation. • The intensity of both blue and yellow emissions increases up to x = 0.03 mol and then decreases rapidly due concentration quenching. Using the simple hydrothermal technique, high-purity nanocrystalline Na+ and Bi3+ co-doped Dy3+ activated LaPO 4 was effectively prepared. The structural characterisation of the prepared samples was carried out using XRD, EDS, SEM and FTIR analysis. The existence of Na+, Dy3+, La3+, P5+, O2– and Bi3+ was demonstrated using EDS analysis. The direct band gap value of 4.72 eV is obtained from UV visible absorption spectrum and infer that the doped samples are suitable for optical applications. The photoluminescence excitation spectrum monitored at 474 nm and 570 nm emission, the Na+ and Bi3+ co-doped Dy3+ activated LaPO 4 exhibit narrow, and intense characteristics f-f peak of Dy3+ ion at 349 nm, 363 nm, 386 nm and 452 nm. Photoluminescence emission spectrum, monitored under 349 nm, 363 nm and 386 nm shows high intense sharp blue emission peaks of Dy3+ with stark splitting at 475 nm, 478 nm, and 486 nm, yellow emission at 571 nm and 580 nm and a very feeble peak at 658 nm in the red region. When the sample is excited at 452 nm only a yellow band is present. Since the intensity of blue and yellow emission in this host matrix is so high and nearly equal, it is appropriate for cool white emission under 350 nm, 363 nm and 386 nm (near UV) excitation and under 452 nm (blue LED) excitation the prepared phosphor may emerge as highly efficient warm white light emitter suitable for general solid-state lighting applications, which can be further confirmed by CIE chromaticity analysis of the prepared sample. In photoluminescence excitation and emission spectra intensities of peaks of the samples with Bi3+ are more intense, this confirms the positive impact of co-doping of Bi3+ into the sample. The Q value from the Dexter's formula is calculated as an average of 6.4 and is very close to 6 indicates that the interaction is dipole − dipole, which causes the non-radiative energy migration among the Dy3+ ions in the sample. The lifetime of characteristic yellow emission of Dy3+ in the Na+ and Bi3+ co-doped Dy3+ activated LaPO 4 host matrix monitored under 350 nm is calculated as 0.642 ms from decay analysis, fitted by a bi-exponential function. The results support the idea that co-doping of Bi3+ and Na+ into the LaPO 4 :Dy3+ matrix could emerge as a potential white light emitting phosphor for phosphor-converted white LED application. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) material is currently a research hotspot in organic light‐emitting diodes (OLEDs) due to their high color purity and high exciton utilization. However, there are only a handful of MR‐TADF emitters with emissions beyond the blue‐to‐green region. The very limited emission colors for MR‐TADF emitters are mainly caused by the fact that so far molecular modifications of MR‐TADF do not offer much change in the emission colors. Here, we report a new approach to modifying a prototypical MR core of DABNA by fusing carbazoles to the MR framework. The carbazole‐fused molecule (TCZ‐F‐DABNA) basically maintains the MR‐dominated features of DABNA while red‐shifting the emission. Its OLED achieves an external quantum efficiency of 39.2 % with a peak at 588 nm, which is a record‐high efficiency for OLEDs with peaks beyond 560 nm. This work provides a new approach for significantly tunning emission colors of MR‐TADF emitters. [ABSTRACT FROM AUTHOR]

Upconversion materials capable of converting low-energy excitation photons into high-energy emission photons have attracted considerable interest in recent years. However, the low upconversion luminescence seriously hinders the application of upconversion phosphors. Heavy lanthanide doping without concentration quenching represents a direct and effective method to enhance the emission intensity. In this study, Er3+ heavy doped Gd2(MoO4)3 phosphor with a monoclinic phase was prepared by a sol–gel process. Under excitation at 976 nm, Gd2(MoO4)3:Er3+ phosphor emitted remarkably intense green emission, and Er3+ concentration up to 20 mol% did not cause concentration quenching. Here, we discuss the upconversion mechanism and concentration quenching. When the Er3+ concentration was in the range of 30–60 mol%, the concentration quenching was governed by the electric dipole–dipole interaction, and when the concentration was greater than 60 mol%, the concentration quenching was controlled by the exchange interactions. The result provides a schematic basis for identifying a phosphor host with heavy lanthanide doping. [ABSTRACT FROM AUTHOR]