Crystal-site engineering control for the reduction of Eu(3+) to Eu(2+) in CaYAlO4: structure refinement and tunable emission properties

A novel white Y2(Ti0.8Hf0.2)2O7: Eu phosphors regulated by HfO2 exhibiting low color shifting for high temperature

The development of white phosphors that can be activated in near-ultraviolet light is highly important in the field of LED lighting. In this work, a series of color-tunable Y2(Ti1-xHfx)2O7:Eu phosphors were prepared by adjusting the HfO2 and Eu3+ concentrations. In particular, white Y2(Ti0.8Hf0.2)2O7:Eu phosphors were successfully synthesized and emitted a broad band covering the entire visible light region upon excitation with 340 nm UV light. The white banded materials were composed of Eu2+ and Eu3+ emissions and HfO2 defect emission. The formation of Eu2+ ions was caused by the introduction of HfO2, which causes self-reduction of Eu3+ ions but does not require additional reducing agents. The white Y2(Ti0.8Hf0.2)2O7:Eu phosphors exhibit low color shifting at high temperature, which is very important for LED applications. The chromaticity shift of the Y2(Ti0.8Hf0.2)2O7:0.2Eu phosphor is 2.83 × 10-2 at 503 K, which is only 54.8 % that of commercial three-color white phosphors at the same temperature. The Ra value did not decrease significantly with increasing temperature and reached 90.2 at 383 K. Y2 (Ti0.8Hf0.2)2O7:0.2Eu phosphors were assembled with a 365 nm LED chip to fabricate a WLED device that showed excellent white-colored coordinates (0.345, 0.358) and a high Ra value of 90.1 under a 300 mA current.

Unravelling the interplay of local structure and valence transitions in Ce-doped CaYAlO4 luminescent materials

Cerium has been widely used as a dopant in luminescent materials due to its unique electronic configurations. It is generally anticipated that the luminescence properties of rare-earth-doped materials are closely related to the local environment of activators, especially for Ce3+ . In addition, it is convenient to modulate its emission wavelength by adjusting the composition and structure. In this study, we systematically analyzed the microstructure of the Ce-doped CaYAlO4 system at atomic resolution. The quantitive results indicated that the structure distortion greatly influenced the valence state of the Ce dopant, which is critical to its luminescence efficiency. In addition, valence variations also exist from surface to inner structure due to the big distortion area around the surface. Our results unravel the interplay of local structure and valence transitions in Ce-doped aluminate phosphors, which has the potential to be applied in other luminescent materials.

Achieving excitation wavelength-power-dependent colorful luminescence via multiplexing of dual lanthanides in fluorine oxide particles for multilevel anticounterfeiting

The optical characteristics of multimode luminescent materials like multimode luminescence (photoluminescence, afterglow, thermoluminescence) and a multi-excitation source (light, thermal, mechanical force) play crucial roles in optical data storage and readout, document security and anticounterfeiting. A higher level of advanced anticounterfeiting may rely on multimode anticounterfeiting materials that can realize multicolor luminescence. Here, a highly integrated multimode and multicolor Y7O6F9:Er3+,Eu3+ material is developed through multiplexing of dual lanthanides in fluorine oxide particles. In photoluminescence and photoluminescence/up-conversion luminescence modes, the material Y7O6F9:Er3+,Eu3+ has the characteristic of excitation wavelength and power dependence. In the photoluminescence mode, under excitation at 254 nm and 365 nm, Y7O6F9:Er3+ and Y7O6F9:Eu3+ showed bright red and green emissions, respectively. In the photoluminescence/up-conversion mode, under the increased excitation power from 0.2 to 2.0 W cm-2, the color of luminescence emission can be finely tuned from red to orange, yellow and green. Taking this unique excitation wavelength-power-dependent luminescence property into account, a multilevel anticounterfeiting device with the Lily pattern was designed. The device readily integrates the advantages of the excitation wavelength-dependent photoluminescence emissions and excitation power-dependent photoluminescence emissions in one overall device. These findings offer unique insight for designing highly integrated multimode, multicolor luminescence materials and advanced anticounterfeiting technology toward a wide variety of applications, particularly multilevel anticounterfeiting devices.

Influence of Mn2+ and Eu3+ Concentration on Photoluminescence and Thermal Stability Properties in Eu3+-Activated ZnMoO4 Red Phosphor Materials

The integration of trivalent europium ion (Eu3+)-doped zinc molybdate (ZnMoO4) as red phosphors in next-generation solid-state lighting (SSL) is impeded by their extended electron lifetime and suboptimal thermal stability. To overcome these limitations, we propose a co-doping approach by incorporating Mn2+ and Eu3+ in ZnMoO4, aiming to improve thermal reversibility and reduce the lifetime of electron transitions. A series of Eu3+-doped ZnMoO4 and Mn2+/Eu3+-co-doped ZnMoO4 phosphor materials were synthesized via the conventional sol-gel method, and their photoluminescence properties were compared under high-temperature conditions. Experimental results indicate that the introduction of Mn2+ into Eu3+-doped ZnMoO4 leads to a decrease in quantum efficiency and electron lifetime, primarily attributed to defects within the crystal lattice and energy transfer from Eu3+ to Mn2+, resulting in enhanced non-radiative transitions. However, the addition of a small quantity of Mn2+ remarkably improves the thermal stability and reversibility of the phosphors. Consequently, this co-doping strategy presents a promising avenue for expanding the application possibilities of phosphor materials, particularly for high-power SSL applications subjected to elevated temperatures. Hence, Eu3+-only doped samples are well-suited for lighting applications due to their high IQE and excellent thermal stability. Conversely, Eu3+/Mn2+-co-doped samples show promise in applications that require a shorter electron lifetime and good reversibility.

Tetrahedrally coordinated rigid crystal structure enables partial self-reduction of mixed-valence europium for optical thermometric application

Mixed-valence europium-activated phosphors are receiving attention in many fields, such as lighting, anti-counterfeiting, optical recording, encryption, and temperature sensing. However, it remains difficult to construct mixed-valence europium-activated compounds due to the reductive and oxidative synthesis conditions required to obtain Eu²⁺ and Eu³⁺ ions, respectively. Herein, mixed-valence Eu²⁺/Eu³⁺ was realized in the CaBPO₅ built by rigidly connected BO₄ and PO₄ tetrahedrons by partial Eu³⁺ → Eu²⁺ self-reduction in the air atmosphere. Commendably, the CaBPO₅:Eu²⁺/Eu³⁺ phosphor exhibits excellent ratiometric temperature sensing performance with the maximum absolute and relative sensitivity being as high as 0.184 K^-1 and 3.444% K^-1 with good signal discriminability, due to the high and low, respectively, temperature-dependence of Eu²⁺ and Eu³⁺ emissions. The rapid dropping intensity of Eu²⁺ in CaBPO₅ with increasing temperature was due to the small energy gap (∼0.48 eV) between the Eu²⁺-5d state and the conduction band. Our work not only provides a novel thermometer candidate but also enlightens researchers to a method of effectively designing new mixed-valence metal-ion activated luminescent thermometers via selective tetrahedrally coordinated rigid crystal structure.

Synthesis of L10 -Iron Triad (Fe, Co, Ni)/Pt Intermetallic Electrocatalysts via a Phosphide-Induced Structural Phase Transition

Structurally ordered L1₀ -iron triad (Fe, Co, Ni)/Pt with a M(iron triad)/Pt ratio ≈1:1 has drawn increasing attention in oxygen reduction reaction (ORR) electrocatalysis and fuel cell technologies by virtue of the high performance derived from their strong surface strain. However, the synthesis of intermetallic L1₀ -M(iron triad)Pt generally requires the accurate content control of the multicomponent and the sufficient thermal energy to overcome the kinetic barrier for atom diffusion. This work reports a synthesis of sub ≈5 nm L1₀ -intermetallic nanoparticles using phosphide intermediate-induced structural phase transition. Taking the L1₀ -CoPt intermetallic, for example, the formation of the L1₀ structure depends on the Co₂ P intermediates can provide abundant P vacancies to accelerate the Pt diffusion into the orthorhombic Co-rich skeletons, instead of the traditional route of intermetallic from solid solution. L1₀ -CoPt prepared by this method has a high degree of ordering and shows the broad adaptability of various Pt-based electrocatalysts with different loading and states to improve their electrocatalytic performance. Additionally, the other L1₀ -M(iron triad)Pt intermetallics, i.e., L1₀ -NiPt and L1₀ -FePt, are also prepared through this phosphide-induced phase transition. The findings provide a promising strategy for designing other intermetallic materials alloy materials using a structural phase transition induced by a second phase.

Governing the crystallographic sites for tuning Eu2+ emission in an apatite oxyfluoride host to be applied for superior white light emitting diodes

Single white light-emitting phosphors for near-UV-converted white light-emitting diodes (WLEDs) are the best alternatives to tricolour phosphor blends and blue light converted yellow-emitting garnets. Nevertheless, achieving white light with elevated colour rendering (CRI) from a single-phase phosphor activated with a lone activator ion is a major challenge. This study aimed at the generation of white light from a single-phase composition activated only with europium. The study started with structural evaluations of Eu³⁺-activated Ca₄La₆Si₆O₂₄F₂ phosphors using X-ray diffraction (XRD) and Eu³⁺ photoluminescence to elucidate the local environment of rare-earth ions and the symmetric nature of the lattice sites. Ca₄La₆Si₆O₂₄F₂ crystallized in the hexagonal P6₃/m space group. The predominant ⁵D₀-⁷F₂ electric dipole transition at 614 nm, and the non-splitting as well as the zero-shifting behaviour of ⁵D₀-⁷F₀ at 578 nm, suggested that the rare-earth ionic substitutions preferably took place at the larger asymmetric sites. Introducing Sr²⁺ ions in Ca₄La₆Si₆O₂₄F₂:Eu³⁺/Eu²⁺ that is synthesized under a reducing atmosphere suppressed Eu³⁺ emission. From the optimized Ca_1.98Sr_1.98La₆Si₆O₂₄F₂:0.04Eu²⁺, a sequence of M²⁺-codoped (M = Mg/Ba) Ca_1.98Sr_1.98La₆Si₆O₂₄F₂:0.04Eu²⁺ phosphors were further developed. The substitutions of Mg²⁺ and Ba²⁺ altered the crystal field by changing the lattice parameters. The Mg²⁺ -doped samples showed a blue-shift from 520 nm (Mg²⁺ = 0) to 471 nm (Mg²⁺ = 1.0), whereas the Ba²⁺-doped compositions showed a red-shift from 520 nm (Ba²⁺ = 0) to 536 nm (Ba²⁺ = 1.2). The change of symmetry owing to the Mg²⁺/Ba²⁺ substitution could have led to the centroid shift, which was responsible for the blue- or red-shift of the emission spectra. The XRD of Ca_1.38Sr_1.38La₆Si₆O₂₄F₂:0.04Eu²⁺,1.2Ba²⁺ indicated a Ba²⁺-induced lattice site expansion. Keeping this in view, the Eu²⁺ ions concentrations were further enhanced from 0.04 to 0.3, and the resultant photoluminescence was further enhanced and red-shifted. The optimized sample showed better intensity compared with the commercial Y₃Al₅O₁₂:Ce³⁺ and exhibited decent photoluminescence above 70% at 150 °C as compared with that at room temperature. Finally, several prototype WLEDs were fabricated using the single phosphor Ca_1.365Sr_1.365La₆Si₆O₂₄F₂:0.07Eu²⁺,1.2Ba²⁺ with near-UV and violet-LED chips. The outcomes indicated the promising nature of this single-composition phosphor for indoor lighting.

Self-reduction-induced BaMgP2O7:Eu2+/3+: a multi-stimuli-responsive phosphor for X-ray detection, anti-counterfeiting and optical thermometry

Mixed-valence Eu^2+/3+-activated phosphors have attracted wide attention due to their excellent luminescence tunability. Steady control of the Eu²⁺/Eu³⁺ ratio is the key to achieving reproducible Eu^2+/3+ co-doped materials. In this work, BaMgP₂O₇:xEu^2+/3+ (BMPO:Eu, x = 0.001-0.20) was successfully prepared by the traditional solid-state method in air. Eu³⁺ undergoes selective self-reduction at Ba²⁺ sites surrounded by a [P₂O₇] framework, leading to quantitive Eu²⁺/Eu³⁺. The phosphors exhibit a blue-violet emission band at ∼410 nm due to 5d-4f transitions of Eu²⁺ and a group of red emission peaks from ⁵D₀-⁷F_J of Eu³⁺. Controllable multicolor emissions are realized by regulating the Eu content and excitations. A linear response of overall luminescence intensity to irradiation dose makes the phosphor appropriate for X-ray detection. The combination of UV-blue excitation-dependent color evolution and X-ray luminescence qualifies the phosphors with great potential for multi-level anti-counterfeiting. In addition, Eu³⁺ presents abnormal anti-thermal quenching, so that the fluorescence intensity ratio (FIR) of Eu²⁺/Eu³⁺ changes in the temperature range of 300-520 K, suggesting a promising application in optical thermometry. Therefore, selectively partial self-reduction in a multi-cationic host is an effective strategy to design mixed-valence co-doped materials, providing a multiplicity of applications.

Sensitive and Reliable Fluorescent Thermometer Based on a Red-Emitting Li2MgHfO4:Mn4+ Phosphor

Contactless fluorescent thermometers are rapidly gaining popularity due to their sensitivity and flexibility. However, the development of sensitive and reliable non-rare-earth-containing fluorescent thermometers remains a significant challenge. Here, a new rare-earth-free, red-emitting phosphor, Li₂MgHfO₄:Mn⁴⁺, was developed for temperature sensing. An experimental analysis combined with density functional theory and crystal field calculations reveals that the sensitive temperature-dependent luminescence arises from nonradiative transitions induced by lattice vibration. Li₂MgHfO₄:Mn⁴⁺ also exhibits reliable recovery performance after 100 heating-cooling cycles due to the elimination of surface defects, which is rare but vital for practical application. This study puts forward a new design strategy for fluorescent thermometers and sheds light on the fundamental structure-property relationships that guide sensitive temperature-dependent luminescence. These considerations are crucial for developing next-generation fluorescence-based thermometers.

Regulation of Local Site Structures to Stabilize Mixed-Valence Eu2+/3+ under a Reducing Atmosphere for Multicolor Photoluminescence

Co-doping mixed-valence Eu^2+/3+ in a single-phase phosphor is an efficient method to realize the emission color regulation, which holds great potential for anticounterfeiting and ratiometric temperature sensing. Here, the mixed-valence Eu-doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F (0 ≤ x ≤ 0.25) phosphors were designed and prepared under a reducing atmosphere. The correlation of local phase structures and luminescence properties was discussed. Replacing Si⁴⁺-Li⁺ ion pairs with Al³⁺-Sr²⁺ ion pairs compresses the Sr sites occupied by Eu²⁺, and it stabilizes Eu³⁺ in a reducing atmosphere and leads to the coexistence of Eu²⁺ and Eu³⁺ in single-phase Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu (0 ≤ x ≤ 0.25) phosphors. Based on the wavelength-dependent luminescence color behaviors of Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors, the fluorescent anticounterfeit papers/patterns containing Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors were the same as ordinary paper under ambient conditions. However, the hidden colors or images can be read out with green-orange luminescence under 365/300 nm light excitation. Benefiting from the diverse thermal response emission behaviors of Eu²⁺ (530 nm) and Eu³⁺ (703 nm), Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors exhibit temperature sensing performances, with the maximum absolute and relative sensitivity being 0.0294 K^-1 at 573 K and 0.83% K^-1 at 348 K. More importantly, Sr_1.95+xLi_1-xSi_1-xAl_xO₄F:0.05Eu phosphors showed excellent stability in humid, acid, and alkali environments, which contributed to applying mixed-valence Eu^2+/3+-doped Sr_1.95+xLi_1-xSi_1-xAl_xO₄F to the fields of multicolor anticounterfeiting and noncontact optical thermometry.

Enhanced luminescence and tunable color in [Eu2+, Si4+]/Mn2+ doped K2BaCa(PO4)2 based on charge compensation and energy transfer

Recently, using the Eu2+ → Mn2+ energy transfer strategy to explore new single-phase phosphors suitable for the near-ultraviolet (n-UV) region has become one of the major strategies in solid-state lighting applications. Therefore, a novel color-tunable K2BaCa(PO4)2 (KBCPO):[Eu2+,Si4+],Mn2+ phosphor was developed because of the preeminent thermal stability of luminescence of Eu2+-activated KBCPO. In this study, we first designed a [Eu2+, Si4+] → [K+, P5+] charge compensation strategy to optimize the luminescence properties of Eu2+ in the KBCPO matrix. In terms of the obtained KBCPO:[Eu2+,Si4+] phosphor, this charge compensation method on the one hand strengthens the emission of Eu2+, and on the other hand, it dramatically improves the thermal stability of luminescence. In particular, the emission intensity of the KBCPO:0.03[Eu2+,Si4+] sample at 548 K can reach 103% relative to that at the initial temperature of 298 K. Based on this charge compensation strategy, we finally obtained a new dual emission KBCPO:[Eu2+,Si4+],Mn2+ phosphor. The analysis of the luminescence properties indicates that the emission enhancement of Mn2+ in KBCPO:[Eu2+,Si4+],Mn2+ stems from the energy transfer of Eu2+ → Mn2+ with the mechanism of the electric dipole-dipole interaction when excited at 365 nm. In addition, KBCPO:[Eu2+,Si4+],Mn2+ also has excellent thermal stability and the emission color could be easily tuned from cyan to orange only by adjusting the Eu2+ doping level. These results confirm that the KBCPO:[Eu2+,Si4+],Mn2+ phosphor is a viable candidate for n-UV white light emitting diodes.

Enhanced luminescence properties of Ca1+xSr2−xAl2O6:Eu3+ (0 ≤ x ≤ 1) red phosphors based on composition modulation

A series of Ca_1+xSr_2−xAl₂O₆:Eu³⁺ (0 ≤ x ≤ 1) red-emitting phosphors with adjustable optical properties and excellent quantum efficiency was developed for potential applications in warm WLEDs.

Photoluminescence and Stoichiometry Correlation in Nanocrystalline EuO x Thin Films: Tunable Color Emission

The development of broadband and ultracompact optoelectronic devices relies on the possibility of fabricating bright and tunable emitters at the nanoscale. Here, we show emission from EuO x (1 ≤ x < 1.4) thin films on silicon formed by nanocrystals with average sizes in the range of 5 nm. The photoluminescence emission of the nano-EuO x films is tunable as a function of the oxygen concentration changing from a green broadband Eu2+-related emission to a narrow red Eu3+-related emission. To reach these results has been instrumental through the use of a new methodology specially designed to achieve high-quality europium oxide films whose compositional properties are controlled by the growth base pressure and preserved thanks to a chemically stable and transparent cover layer of Al2O3. Our findings confirm the outstanding potential of nanostructured EuO x films as "one-compound" optical elements with tunable emission properties for their implementation in integrated silicon-based devices.

Achieving tunable emitting YAl3(BO3)4:Eu phosphors by substituting cations (Sr2+, Ca2+, Ga3+, In3+) and controlling BO3 group polarizability

To explore the influence of the luminescence characteristics and valence state of Eu ions, a series of YAl₃(BO₃)_4−m(PO₄)_m:0.05Eu, Y_0.925−xAC_xL_xBO:0.05Eu, Y_0.925−yAS_yL_yBO:0.05Eu, Y_0.925−zAG_zBO:0.05Eu and Y_0.925−wAI_wBO:0.05Eu phosphors are synthesized.

Different Strategies of Stabilization of Vanadium Oxidation States in Lagao3 Nanocrystals

The spectroscopic properties of LaGaO₃, doped with V ions, were examined in terms of the possibility of the stabilization of particular vanadium oxidation states. It was shown that three different approaches may be applied in order to control the ionic charge of vanadium, namely, charge compensation, via incorporation of Mg²⁺/Ca²⁺ ions, citric acid (CA)-assisted synthesis, with various CA concentrations and grain size tuning through annealing temperature regulation. Each of utilized method enables the significant reduction of V⁵⁺ emission band at 520 nm associated with the V⁴⁺→ O^2- CT transition in respect to the ²E→ ²T₂ emission band of V⁴⁺ at 645 nm and ¹E₂ → ³T_1g emission band of V³⁺ at 712 nm. The most efficient V oxidation state stabilization was obtained by the use of grain size modulation, which bases on fact of different localization of the V ions of given charge in the nanoparticles. Moreover, the CA-assisted synthesis of LaGaO₃:V determines V valence states but also provides significant separation of the nanograins. It was found that superior charge compensation was achieved when Mg²⁺ ions were introduced in the matrix, due the more efficient lability, resulting from the comparable ionic radii between Mg²⁺ and V ions.

Color-tunable visible photoluminescence of Eu:CaF2 single crystals: variations of valence state and local lattice environment of Eu ions

In this article, Eu-activated CaF₂ single crystals were synthesized by Bridgman-Stockbarge method. The dependence of photoluminescence properties of Eu: CaF₂ crystals in UV-Vis regions on EuF₃ doping concentrations were investigated. While the EuF₃ doping concentration is increased from 0.6% to 6.0%, the CIE (Commission Internationale de L'Eclairage) color coordinates of Eu: CaF₂ crystals can be tuned from (0.28, 0.12) to (0.60, 0.38), corresponding to the luminescence color from blue to orange. XPS (X-ray Photoelectron Spectroscopy) measurements indicated that Eu²⁺ and Eu³⁺ ions both existed in the crystals. With EuF₃ doping concentration increasing, the proportion of Eu³⁺ ions increase from 16.73% to 39.00%, while that of Eu²⁺ ions decrease from 83.27% to 61.00%. Moreover, the integrated intensity ratio (R) of the 614 nm to 593 nm of Eu³⁺ ions increase from 0.38 to 0.44, indicating the local lattice environment symmetry of Eu³⁺ ions become lower with higher EuF₃ doping concentrations. Furthermore, the CIE chromaticity coordinates of Eu: CaF₂ crystals greatly depend on the excitation wavelength. The warm white-light emission has been realized in 0.6%Eu: CaF₂ crystal when the excitation wavelength is around 322 nm.

Investigation of local structure distortion and electron cloud interaction on emission-band broadening induced by the concentration perturbation effect of cation substitution in BaY2Si3O10:Eu phosphors

Here, we conceived a concentration perturbation effect to obtain cyan-emitting phosphors based on local structure distortion and electron cloud interaction.

Synthesis of Eu2+/Eu3+ Co-Doped Gallium oxide nanocrystals as a full colour converter for white light emitting diodes

Eu²⁺ and Eu³⁺ co-doped Ga₂O₃ nanocrystals (Ga₂O₃:Eu NCs) were synthesized in an organic phase at a low reaction temperature of 300 °C. The surface of Ga₂O₃:Eu NCs was passivated by oleylamine (OAm) and acetylacetone (acac). The coexistence of Eu²⁺ and Eu³⁺ as well as passivation by acac and OAm enable Ga₂O₃ to be excited in the broad spectral range of 200-500 nm. The broadened absorption band is attributed to the strong acac → Ln(III) ligand to the metal charge transfer transition at ∼370 nm, Eu(III) f-f allowed ⁷F₀ → ⁵L₆ transition at 395 nm, and ⁷F₀ → ⁵D₂ transition at 465 nm, as well as the efficient electronic transition of Eu(II) 4f → 5d at ∼400 nm. Under near-ultraviolet excitation, white light emission can be achieved by combining orange-red light from f-f electronic transition of Eu(III) with blue-green-yellow light from Ga₂O₃ oxygen defects levels. Furthermore, the resultant Ga₂O₃:Eu NCs with optimized quantum yield of 14.5% were coated onto 395 nm near-ultraviolet chips to fabricate a white light emitting diode. It exhibits a luminous efficiency of 34 lm/W, CIE colour coordinate of (0.2964, 0.2831) and high colour rendering index of 80.

Eu3+/2+ co-doping system induced by adjusting Al/Y ratio in Eu doped CaYAlO4: preparation, bond energy, site preference and 5D0-7F4 transition intensity

CaY1-x Al1+x O4:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY1-x Al1+x O4:2%Eu phosphors exhibit both the blue emission of Eu2+ (4f65d1-4f7) and red-orange emission of Eu3+ (5D0-7F1,2,3,4) under UV light excitation, which showed that the Eu3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu3+ ions can be reduced to Eu2+ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity 5D0-7F4 transition peak. The relative intensity of 5D0-7F2 and 5D0-7F4 can be stabilized by changing the relative proportions of Al3+ and Y3+. Furthermore, this was explained by the J-O theory.

Novel Eu3+-activated Ba2Y5B5O17 red-emitting phosphors for white LEDs: high color purity, high quantum efficiency and excellent thermal stability

Eu3+-activated Ba2Y5B5O17 (Ba2Y5-x Eu x B5O17; x = 0.1-1) red-emitting phosphors were synthesized by the conventional high temperature solid-state reaction method in an air atmosphere. Powder X-ray diffraction (XRD) analysis confirmed the pure phase formation of the as-synthesized phosphors. Morphological studies were performed using field emission-scanning electron microscopy (FE-SEM). The photoluminescence spectra, lifetimes, color coordinates and internal quantum efficiency (IQE) as well as the temperature-dependent emission spectra were investigated systematically. Upon 396 nm excitation, Ba2Y5-x Eu x B5O17 showed red emission peaking at 616 nm which was attributed to the 5D0 → 7F2 electric dipole transition of Eu3+ ions. Meanwhile, the influences of different concentrations of Eu3+ ions on the PL intensity were also discussed. The optimum concentration of Eu3+ ions in the Ba2Y5-x Eu x B5O17 phosphors was found to be x = 0.8. The concentration quenching mechanism was attributed to the dipole-dipole interaction and the critical distance (R c) for energy transfer among Eu3+ ions was determined to be 5.64 Å. The asymmetry ratio [(5D0 → 7F2)/(5D0 → 7F1)] of Ba2Y4.2Eu0.8B5O17 phosphors was calculated to be 3.82. The fluorescence decay lifetimes were also determined for Ba2Y5-x Eu x B5O17 phosphors. In addition, the CIE color coordinates of the Ba2Y4.2Eu0.8B5O17 phosphors (x = 0.653, y = 0.345) were found to be very close to the National Television System Committee (NTSC) standard values (x = 0.670, y = 0.330) of red emission and also showed high color purity (∼94.3%). The corresponding internal quantum efficiency of the Ba2Y4.2Eu0.8B5O17 sample was measured to be 47.2%. Furthermore, the as-synthesized phosphors exhibited good thermal stability with an activation energy of 0.282 eV. The above results revealed that the red emitting Ba2Y4.2Eu0.8B5O17 phosphors could be potential candidates for application in near-UV excited white light emitting diodes.

Luminescent Lanthanide MOFs: A Unique Platform for Chemical Sensing

In recent years, lanthanide metal-organic frameworks (LnMOFs) have developed to be an interesting subclass of MOFs. The combination of the characteristic luminescent properties of Ln ions with the intriguing topological structures of MOFs opens up promising possibilities for the design of LnMOF-based chemical sensors. In this review, we present the most recent developments of LnMOFs as chemical sensors by briefly introducing the general luminescence features of LnMOFs, followed by a comprehensive investigation of the applications of LnMOF sensors for cations, anions, small molecules, nitroaromatic explosives, gases, vapors, pH, and temperature, as well as biomolecules.

Neutralizing the Charge Imbalance Problem in Eu3+-Activated BaAl2O4 Nanophosphors: Theoretical Insights and Experimental Validation Considering K+ Codoping

In recent years, rare-earth-doped nanophosphors have attracted great attention in the field of luminescent materials for advanced solid-state lighting and high-resolution display applications. However, the low efficiency of concurrent red phosphors creates a major bottleneck for easy commercialization of these devices. In this work, intense red-light-emitting K⁺-codoped BaAl₂O₄:Eu³⁺ nanophosphors having an average crystallite size of 54 nm were synthesized via a modified sol-gel method. The derived nanophosphors exhibit strong red emission produced by the ⁵D₀ → ⁷F _J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ upon UV and low-voltage electron beam excitation. Comparative photoluminescence (PL) analysis is executed for Eu³⁺-activated and K⁺-coactivated BaAl₂O₄:Eu³⁺ nanophosphors, demonstrating remarkable enhancement in PL intensity as well as thermal stability due to K⁺ codoping. The origin of this PL enhancement is also analyzed from first-principles calculations using density functional theory. Achievement of charge compensation with the addition of a K⁺ coactivator plays an important role in increasing the radiative lifetime and color purity of the codoped nanophosphors. Obtained results substantially approve the promising prospects of this nanophosphor in the promptly growing field of solid-state lighting and field emission display devices.

Novel SrLaAlO4:Mn4+deep-red emitting phosphors with excellent responsiveness to phytochrome PFRfor plant cultivation LEDs: synthesis, photoluminescence properties, and thermal stability

Herein, novel rare-earth-free Mn⁴⁺-doped SrLaAlO₄ deep-red emitting phosphors were successfully synthesized via a traditional solid-state reaction method. The crystal structure and phase purity of the as-prepared samples were confirmed by XRD Rietveld refinement. Photoluminescence properties of SrLaAlO₄:Mn⁴⁺ phosphors were examined in detail using photoluminescence spectra, decay lifetimes, temperature-dependent emission spectra and internal quantum efficiency measurements. The excitation spectrum obtained by monitoring at 730 nm contained two excitation bands centered at 364 and 520 nm within the range of 200–550 nm due to the Mn⁴⁺–O²⁻ charge-transfer band and the ⁴A_2g → ⁴T_1g, ⁴T_2g transitions of the Mn⁴⁺ ions. Under the 364 nm excitation, the SrLaAlO₄:Mn⁴⁺ phosphors exhibited an intense deep-red emission band in 610–790 nm wavelength range peaking at 730 nm, which was assigned to the ²E_g → ⁴A_2g transition of Mn⁴⁺ ions. The deep red emission showed excellent responsiveness to phytochrome P_FR, revealing that the SrLaAlO₄:0.4% Mn⁴⁺ phosphors possessed a possible application in deep-red light-emitting diodes (LEDs) for plant cultivation. The optimal doping concentration of Mn⁴⁺ ions was found to be 0.4 mol%. The critical distance R_c for energy transfer among Mn⁴⁺ ions was determined to be 5.86 Å and the concentration quenching mechanism was confirmed to be the electric dipole–dipole interaction. In addition, the Commission International de I'Eclairage (CIE) colour coordinates of the SrLaAlO₄:0.4% Mn⁴⁺ phosphors (0.734, 0.266) were located in the deep red region and the corresponding internal quantum efficiency was measured to be about 29%. The above results confirmed that the as-prepared SrLaAlO₄:0.4% Mn⁴⁺ deep red emitting phosphors might be a potential candidate for plant cultivation LEDs.

Novel Mn⁴⁺ activated SrLaAlO₄ deep-red emitting phosphors with excellent responsiveness to phytochrome P_FR were developed for plant cultivation LEDs.

Morphology control and photoluminescence properties of Eu3+-activated Y4Al2O9 nanophosphors for solid state lighting applications

Spherical Eu³⁺:Y₄Al₂O₉ nanophosphors exhibit brilliant PL behavior with enhanced color purity and excited state lifetime.

A strategy for realizing tunable luminescence and full-color emission in Sr3Gd2(Si3O9)2:Eu phosphors by introducing dual functional Mn2+

The introduced Mn²⁺ ion can act as both an activator and a structure regulator in the SGSO:Eu system to achieve full-color emission and tunable luminescence of SGSO:0.03Eu,Mn phosphors.

Bond energy, site preferential occupancy and Eu2+/3+ co-doping system induced by Eu3+ self-reduction in Ca10M(PO4)7 (M = Li, Na, K) crystals

Ca₁₀M(PO₄)₇:Eu (M = Li, Na, K) phosphors have been synthesized via a solid-state reaction process, their phase purity was examined using XRD patterns, and Rietveld refinement confirmed that the Ca₁₀Li(PO₄)₇, Ca₁₀Na(PO₄)₇ and Ca₁₀K(PO₄)₇ are pure phases.

Tuning of luminescence properties by controlling an aid-sintering additive and composition in Na(Ba/Sr/Ca)PO4:Eu2+ for white LEDs

A series of Na(Ba/Sr/Ca)PO₄:Eu²⁺ phosphors were prepared via a high-temperature solid-state reaction method.

Cation–anion substitution induced spectral tuning and thermal stability optimization in Sr2SiO4:Eu phosphors

The cation–anion substitution results in spectral tuning and thermal stability optimization in Sr₂Si_1−xAl_xO_4−2xN_x:Eu phosphors.

Enhance Color Rendering Index via Full Spectrum Employing the Important Key of Cyan Phosphor

A new concept called "full-spectrum lighting" has attracted considerable attention in recent years. Traditional devices are usually combined with ultraviolet-light-emitting diode (LED), red, green, and blue phosphors. However, a cyan cavity exists in the 480-520 nm region. Hence, cyan phosphors are needed to compensate for the cavity. (Sr,Ba)₅(PO₄)₃Cl:Eu²⁺ phosphors feature an extremely unique and tunable photoluminescence spectrum. Nevertheless, the tuning mechanisms of these phosphors remain unclear. In this study, we elucidate the mechanism of the cation size-controlled activator uneven-occupation and reoxidation in (Sr,Ba)₅(PO₄)₃Cl:Eu²⁺ phosphors. This mechanism could help tune the optical properties of related apatite families and structures with multiple cation sites and strongly uneven occupation of activators and cations. Finally, the package of the LED device is constructed to show that both color rendering index Ra and R9 are higher than 95. Thus, the device could be a potential candidate for full-spectrum lighting.

Single Component Lanthanide Hybrids Based on Metal-Organic Framework for Near-Ultraviolet White Light LED

Near-UV single-phase white-light phosphor (Eu0.045Tb0.955CPOMBA/La0.6Eu0.1Tb0.3CPOMBA) based on metal-organic framework was prepared by in situ doping isostructural lanthanide MOF with Eu(3+) and Tb(3+), and it is found that the energy can effectively transfer from organic ligand to lanthanides, which can overcome weak absorption under direct excitation of lanthanide ions due to the forbidden f-f transitions. The photoluminescence and thermostability of the new MOF phosphor are investigated, and effective white-light emission is achieved under 365 and 380 nm excitations. By employing Eu0.045Tb0.955CPOMBA as phosphor, we fabricated a near-ultraviolet white-light-emitting diode (n-UV WLED) (365 nm) with low CCT (5733 K), high CRI (Ra = 73.4), and CIE chromaticity coordinate (0.3264, 0.3427). This approach may open new perspectives for developing single-phase UV phosphors.

Luminescence properties of Eu2+-doped BaSi2O5 as an efficient green phosphor for light-emitting devices and wide color gamut field emission displays

A green-emitting BaSi₂O₅:Eu²⁺ phosphor for white light emitting diodes and field emission displays.