Enhancing Luminescence and Controlling the Mn Valence State of Gd3Ga5-x-δAlx-y+δO12:yMn Phosphors by the Design of the Garnet Structure

Micro-Inclusion Engineering via Sc Incompatibility for Luminescence and Photoconversion Control in Ce3+-Doped Tb3Al5-xScxO12 Garnet

Aluminum garnets display exceptional adaptability in incorporating mismatching elements, thereby facilitating the synthesis of novel materials with tailored properties. This study explored Ce3+-doped Tb3Al5-xScxO12 crystals (where x ranges from 0.5 to 3.0), revealing a novel approach to control luminescence and photoconversion through atomic size mismatch engineering. Raman spectroscopy confirmed the coexistence of garnet and perovskite phases, with Sc substitution significantly influencing the garnet lattice and induced A1g mode softening up to Sc concentration x = 2.0. The Sc atoms controlled sub-eutectic inclusion formation, creating efficient light scattering centers and unveiling a compositional threshold for octahedral site saturation. This modulation enabled the control of energy transfer dynamics between Ce3+ and Tb3+ ions, enhancing luminescence and mitigating quenching. The Sc admixing process regulated luminous efficacy (LE), color rendering index (CRI), and correlated color temperature (CCT), with adjustments in CRI from 68 to 84 and CCT from 3545 K to 12,958 K. The Ce3+-doped Tb3Al5-xScxO12 crystal (where x = 2.0) achieved the highest LE of 114.6 lm/W and emitted light at a CCT of 4942 K, similar to daylight white. This approach enables the design and development of functional materials with tailored optical properties applicable to lighting technology, persistent phosphors, scintillators, and storage phosphors.

An efficient blue-violet phosphor: an advanced material designed for high-quality full-spectrum lighting

A highly efficient phosphor with exceptional luminescence properties is crucial for achieving high-quality solid-state white-light illumination. Here, this paper presents a groundbreaking discovery, an innovative blue-violet emitting Ba1.31Sr3.69(BO3)3Cl:Ce3+ (BSBCl:Ce3+) phosphor designed with remarkable thermal stability and quantum efficiency for full spectrum white light-emitting diodes (WLEDs). By employing a high-temperature solid-phase method, we synthesized various BSBCl:xCe3+ phosphors with different Ce3+ doping concentrations. Remarkably, BSBCl:0.03Ce3+ displays a broad excitation band from 250 nm to 400 nm, rendering it compatible with commercial near-ultraviolet (UV) LED chips. Under 330 nm excitation, this phosphor emits blue light with an astonishing 88.2% internal quantum efficiency (IQE) and an impressive 60.9% external quantum efficiency (EQE). Notably, when employed in the temperature range of 298-473 K, the synthesized BSBCl:0.03Ce3+ phosphor exhibits exceptional color stability and thermal stability (I423 K/I298 K = 83%). Utilizing BSBCl:0.03Ce3+ as the blue-violet emitting component in the fabrication of WLED devices has demonstrated significant advancements in the color rendering index. These findings underscore the potential of BSBCl:Ce3+ phosphors for a wide range of applications in health-oriented indoor illumination.

Crystal Field Engineering Yields New 3D Layered Solid Solution Phosphors (Ca/Sr)4MgAl2Si3O14:Eu2+ for White-Light-Emitting Diode Full-Spectrum Lighting

The cation-equivalent substitution strategy has the ability to manipulate the luminescence color of phosphors and enhance their overall luminescence performance. A series of novel yellow feldspar-type 3D layered phosphors (Ca1-ySry)4MgAl2Si3O14:xEu2+ were synthesized using a high-temperature solid-state reaction. The solid solution phosphors belong to a tetragonal crystal system with a space group of P4̅21m and cell parameters of a = b = 7.75407-7.91794 Å, c = 5.04299-5.22543 Å, and V = 303.166-327.602 Å3. Under near-ultraviolet (n-UV) excitation, the luminescence color of the phosphor undergoes modulation from yellow-green (530 nm) to blue (467 nm) as the Sr2+ ion substitution ratio increases. This modulation is attributed to the gradual decrease in crystal field splitting energy. Additionally, both the Stokes shift and the full width of the luminescence spectra decrease. Furthermore, there is an increase in the quantum yield (QY) from 45.50 to 60.73%. Finally, the fabricated white-light-emitting diode devices emitted warm white light and achieved high Ra (Ra = 94, 96.6, 92.7) and low correlated color temperature (CCT = 3486, 3430, 3788 K), indicating that the prepared solid solution phosphors can be used as candidate materials for WLED lighting.

Single-Atom and Dual-Atom Electrocatalysts: Synthesis and Applications

Distinguishing themselves from nanostructured catalysts, single-atom catalysts (SACs) typically consist of positively charged single metal and coordination atoms without any metal-metal bonds. Dual-atom catalysts (DACs) have emerged as extended family members of SACs in recent years. Both SACs and DACs possess characteristics that combine both homogeneous and heterogeneous catalysis, offering advantages such as uniform active sites and adjustable interactions with ligands, while also inheriting the high stability and recyclability associated with heterogeneous catalyst systems. They offer numerous advantages and are extensively utilized in the field of electrocatalysis, so they have emerged as one of the most prominent material research platforms in the direction of electrocatalysis. This review provides a comprehensive review of SACs and DACs in the field of electrocatalysis: encompassing economic production, elucidating electrocatalytic reaction pathways and associated mechanisms, uncovering structure-performance relationships, and addressing major challenges and opportunities within this domain. Our objective is to present novel ideas for developing advanced synthesis strategies, precisely controlling the microstructure of catalytic active sites, establishing accurate structure-activity relationships, unraveling potential mechanisms underlying electrocatalytic reactions, identifying more efficient reaction paths, and enhancing overall performance in electrocatalytic reactions.

Equivalent chemical substitution in double-double perovskite-type ALaLiTeO6:Mn4+ (A = Ba2+, Sr2+, Ca2+) phosphors enabling wide range crystal field strength regulation and efficient far-red emission

Mn⁴⁺-activated phosphors have shown wide prospective applications in phosphor-converted white light-emitting diodes (pc-WLEDs) and pc-LEDs used in illumination and indoor plant cultivation, respectively. Recently, double perovskites A₂B'B''O₆ with a tunable crystal structure and versatile octahedral sites have been extensively studied as good host matrixes for Mn⁴⁺-emitters to realize tunable far-red emissions. Herein, a series of double-double perovskite-type ALaLiTeO₆:Mn⁴⁺ (A = Ba, Ba_0.5Sr_0.5, Sr, Sr_0.5Ca_0.5, Ca) phosphors were synthesized and structurally characterized, and the correlations between their structure and luminescence were also studied systematically. With a decrease of the A-cation size, an increased distortion in the average structure and a structure symmetry lowering (I2/m → P2₁/_n) were observed for ALaLiTeO₆:Mn⁴⁺. In contrast, on the local scale, the degree of (Li/Te)O₆-octahedral distortion is positively correlated with the ΔIR value, which is the ionic radius difference between A²⁺ and La³⁺. The local structural changes were found to be irrelevant to the significant improvements in photoluminescence properties. In combination with careful spectroscopic analysis, we deciphered that a decreased A-cation is in fact helpful for the enhancements in crystal field strength (D_q/B = 2.12-2.82) and Mn-O covalent bonding, thereby resulting in an improved quantum efficiency, a suppressed nonradiative transition, and a redshift in photoluminescence spectra. Amongst the ALaLiTeO₆:Mn⁴⁺ phosphor series, CaLaLiTeO₆:Mn⁴⁺ exhibits the highest external quantum efficiency of 70.1% and internal quantum efficiency of 96.4% and superior thermal stability (93.3%@423 K), making CaLaLiTeO₆:Mn⁴⁺ very promising as far-red phosphors for pc-LEDs. The findings of this work will serve as a new guide for rational design of high-performance Mn⁴⁺-activated double-double perovskite-type far-red phosphors.

Tremendous Acceleration of Plant Growth by Applying a New Sunlight Converter Sr4 Al14- x Gax O25 :Mn4+ Breaking Parity Forbidden Transition

Majority of Mn4+ activated oxide phosphors have the wavelength of excitation and emission suitable for acceleration of plant growth as light converter from sunlight to deep red. Here, it is observed that 60% increase of red emission of Sr4 Al14 O25 :0.01Mn4+ is found by substituting 0.1Ga3+ . It is clarified that the increase is originated from a unique mechanism of breaking parity forbidden transition under the substitution of cation in d-d transition by using the tool of special aberration corrected transmission electron microscope(AC-STEM), pre-edge peak (1s→3d) Mn K-edge X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), Rietveld analysis of X-ray diffraction (XRD) patterns, and reflection spectra. Further, a combination of substituted Ga, Mg, and special double flux H3 BO3 /AlF3 is found to tremendously increase the emission intensity (355% up). Actual growth of chlorella and rose is examined by a combination of the cheap Sr4 Al14 O25 :0.01Mn4+ ,0.007Mg2+ ,0.1Ga3+ and a unique reflection typed phosphor-film system as sunlight converting system. Optical density of chlorella and height of rose grass is increased by 36±14% and 174±80% compared with nonphosphor-film, respectively.

Double Perovskite Mn4+-Doped La2CaSnO6/La2MgSnO6 Phosphor for Near-Ultraviolet Light Excited W-LEDs and Plant Growth

Non-rare earth doped oxide phosphors with far-red emission have become one of the hot spots of current research due to their low price and excellent physicochemical stability as the red component in white light-emitting diodes (W-LEDs) and plant growth. Herein, we report novel Mn⁴⁺-doped La₂CaSnO₆ and La₂MgSnO₆ phosphors by high-temperature solid-phase synthesis and analyzed their crystal structures by XRD and Rietveld refinement. Their excitation spectra consist of two distinct excitation bands with the dominant excitation range from 250 to 450 nm, indicating that they possess strong absorption of near-ultraviolet light. Their emission is located around 693 and 708 nm, respectively, and can be absorbed by the photosensitive pigments Pr and Pfr, proving their great potential for plant growth. Finally, the prepared samples were coated with 365 nm UV chips to fabricate far-red LEDs and W-LEDs with low correlation color temperature (CCT = 4958 K/5275 K) and high color rendering index (R_a = 96.4/96.6). Our results indicate that La₂CaSnO₆:Mn⁴⁺ and La₂MgSnO₆:Mn⁴⁺ red phosphors could be used as candidate materials for W-LED lighting and plant growth.

Tuning Multicolor Emission of Manganese-Activated Gallogermanate Nanophosphors by Regulating Mn Ions Occupying Sites for Multiple Anti-Counterfeiting Application

The ability to manipulate the luminescent color, intensity and long lifetime of nanophosphors is important for anti-counterfeiting applications. Unfortunately, persistent luminescence materials with multimode luminescent features have rarely been reported, even though they are expected to be highly desirable in sophisticated anti-counterfeiting. Here, the luminescence properties of Zn₃Ga₂GeO₈:Mn phosphors were tuned by using different preparation approaches, including a hydrothermal method and solid-state reaction approach combining with non-equivalent ion doping strategy. As a result, Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by a hydrothermal method demonstrate an enhanced red photoluminescence at 701 nm and a strong green luminescence with persistent luminescence and photostimulated luminescence at 540 nm. While Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by solid-state reactions combined with a hetero-valent doping approach only exhibit an enhanced single-band red emission. Keeping the synthetic method unchanged, the substitution of hetero-valent dopant ion Li⁺ into different sites is valid for spectral fine-tuning. A spectral tuning mechanism is also proposed. Mn-activated Zn₃Ga₂GeO₈ phosphors synthesized by a hydrothermal approach with multimodal luminescence is especially suitable for multiple anti-counterfeiting, multicolor display and other potential applications.

Compensation effect of electron traps for enhanced fluorescence intensity ratio thermometry performance

How the electron traps in the host matrix impact the fluorescence intensity ratio (FIR) thermometry performance in inorganic phosphors is still unclear. In this work, the relationships between temperature-dependent photoluminescence,...

Multimodal dynamic color-tunable persistent luminescent phosphor Ca3Al2Ge3O12:Mn2+,Cr3+ for anti-counterfeiting and industrial inspection

Ca3Al2Ge3O12:Mn2+,Cr3+ may be used in anti-counterfeiting and industrial inspection.

Thermal stability and self-reduction of a new red phosphor NaMg(PO3)3:Mn2+

For Mn-activated phosphors, the luminescent performance is strongly dependent on the oxidation state of Mn. In this paper, a series of red phosphors NaMg(PO3)3:xMn2+ (NMP:xMn2+) were synthesized by high temperature...

Tuning multicolour emission of Zn2GeO4:Mn phosphors by Li+ doping for information encryption and anti-counterfeiting applications

Traditional fluorescent materials used in the anti-counterfeiting field usually exhibit monochromatic luminescence at a single-wavelength excitation, which is easily forged by sophisticated counterfeiters. In this work, Zn₂GeO₄:Mn,x%Li (x = 0 and 20), Zn₂GeO₄-NaLiGe₄O₉:Mn,x%Li (x = 50 and 70) and NaLiGe₄O₉:Mn micro-phosphors with multi-chromatic and multi-mode luminescence have been successfully synthesized via a hydrothermal approach followed by an annealing treatment. As expected these Li⁺ doped Zn₂GeO₄:Mn and Zn₂GeO₄-NaLiGe₄O₉:Mn phosphors exhibit a double peak emission including a long green afterglow (∼540 nm) and red photoluminescence (∼668 nm). By tuning Li⁺ doping concentrations, a gradual colour output and a tuneable afterglow duration are achieved. In particular, the Zn₂GeO₄:Mn,Li and NaLiGe₄O₉:Mn phosphors exhibit excellent performance as security inks for printing luminescent numbers and anti-counterfeiting patterns, which show an afterglow time-dependent or excitation wavelength-dependent luminescence colour evolution. This work proves the feasibility of the Li⁺ doping strategy in emission tuning, which can stimulate further studies on multi-mode luminescent materials for anti-counterfeiting applications.

Extension of Spectral Shift Controls from Equivalent Substitution to an Energy Migration Model Based on Eu2+/Tb3+-Activated Ba4-xSrxGd3-xLuxNa3(PO4)6F2 Phosphors

Single-phase phosphors with tunable emission colors are crucial to develop high-performance white light-emitting diodes since they are valuable to improve the energy efficiency, color rendering index, and correlated color temperature. Most of the studies have been conducted to control the spectral shifts via a polyhedral distortion or chemical unit cosubstitution strategy. The combination of host optimization and dopant activator design in a single-phase phosphor system is very rare. Herein, a partial substitution strategy of [Ba²⁺-Gd³⁺] by [Sr²⁺-Lu³⁺] has been employed in Ba_4-xSr_xGd_3-x-yLu_xNa₃(PO₄)₆F₂/5% Eu²⁺ (x = 0-0.40) phosphors. Also, the energy migration from Eu²⁺ to Tb³⁺ ions has been investigated in as-prepared samples. Consequently, the emitted signal is observed to shift from 470 to 575 nm derived from equivalent substitutions, which is attributed to specific performance by the emission profile of Eu²⁺, and such results are closely related to splitting of the crystal field and energy transfer among various luminescent centers. Moreover, the tunable yellowish-green emitting material has been assembled by incorporating ion pairs (Eu²⁺ → Tb³⁺) into the Ba_3.85Sr_0.15Gd_2.85Lu_0.15Na₃(PO₄)₆F₂, and their relative ratios are varied. The corresponding Eu²⁺ → Tb³⁺ energy migration process is assigned to be the dipole-quadrupole interaction by the Inokuti-Hirayama model. This work provides rational guidance for the design and discovery of new products with tunable emission colors, originating from the cosubstitution strategy and energy conversion model.

Highly thermally stable Cr3+ and Yb3+ codoped Gd2GaSbO7 phosphors for broadband near-infrared applications

Gd₂GaSbO₇:Cr³⁺,Yb³⁺ phosphors with efficient broadband NIR emission were prepared by a solid-state reaction. Under the excitation of 448 nm, the Gd₂GaSbO₇:Cr³⁺ (GGS:Cr³⁺) phosphor exhibits a broadband NIR emission band centered at approximately 770 nm with a full width at half maximum (FWHM) of 160 nm. In addition, Yb³⁺ codoping can distinctly improve the photoluminescence properties of the GGS:Cr³⁺ phosphor, leading to broadening of the FWHM and greatly enhancing the thermal stability of the phosphor. Moreover, the energy conversion process of Cr³⁺ → Yb³⁺ ions was analyzed in detail, demonstrating that the energy transfer mechanism conformed to electric dipole-dipole interaction. The NIR pc-LEDs assembled with the GGS:Cr³⁺ phosphor and blue LED chips possessed a maximum NIR output power of ∼21 mW at 100 mA driving current, indicating promising applications of the synthesized phosphor in NIR pc-LEDs.

NaLaMgWO6:Mn4+/Pr3+/Bi3+ bifunctional phosphors for optical thermometer and plant growth illumination matching phytochrome PR and PFR

Phytochromes P_R and P_FR distributed in different organs of plant can effectively absorb red and far-red light, respectively. Therefore, plant growth can be controlled by changing the ratio of red light to far-red light. The emission of Pr³⁺ (transition from ³P₀→³F_2,3) and Mn⁴⁺(transition from ²E_g→⁴A_2g) is located at the red and far-red range which matches with the absorption band of P_R and P_FR, respectively. Herein, NaLaMgWO₆:Mn⁴⁺/Pr³⁺/Bi³⁺ phosphors with improving luminescence properties via Bi³⁺ doping have been successfully prepared by the sol-gel method. With the variation of temperature, the photoluminescence (PL) of Pr³⁺/Mn⁴⁺ (corresponding to P_FR/P_R) of titled phosphors can be tuned, which is very useful for controlling the plant growth. Moreover, based on the fluorescence intensity ratios (FIR) of the two activator Mn⁴⁺ and Pr³⁺, the maximum relative sensitivity was approximately 3.39%/K at 298 K. All the results indicated that the titled phosphor is a bifunctional material for plant growth illumination with high matching phytochrome (P_R and P_FR) and temperature sensing with high sensitivity.

Ca[B8 O11 (OH)4 ] : Eu2+ - A Highly Efficient Deep Blue-Emitting Phosphor Prepared by Low-Temperature Self-reduction

Highly efficient inorganic phosphors are crucial for solid-state lighting. In this paper, a new method of low-temperature self-reduction was used for preparing a highly efficient deep blue-emitting phosphor of Ca[B₈ O₁₁ (OH)₄ ] : Eu²⁺ (CBH : Eu²⁺ ). The crystal structure, morphology, chemical state, and photoluminescence (PL) properties of the CBH : Eu²⁺ phosphor have been investigated. By using the screened hybrid function (HSE06), the band gap (E_g ) of CBH was calculated to be 7.48 eV, which is a necessary condition for achieving high quantum yield phosphors. The experiment results show that almost all the added raw materials of Eu³⁺ can be reduced to Eu²⁺ in CBH crystal under a non-reducing atmosphere. The CBH : Eu²⁺ phosphor shows a broad excitation spectrum centered at 277 and 327 nm in the range of 220 to 400 nm, and a narrow-band emission spectrum centered at 428 nm in the range of 400 to 500 nm, with a full width at half maximum (fwhm) of 42.35 nm. Under UV radiation, the CBH : 2 %Eu²⁺ exhibits high photoluminescence quantum yield (PLQY=95.0 %), high external quantum efficiency (EQE=31.1 %), and ultra-high color purity (97.6 %). The PL intensity of CBH : 2 %Eu²⁺ remains 62.6 % of the initial intensity at 150 °C. Finally, the white light-emitting diodes (WLED) fabricated by CBH : 2 %Eu²⁺ , excited by a 365 nm chip, presents outstanding performances with a luminous efficacy (LE) of 13.9 lm/W, a color rendering index (CRI) of 89.4, and a correlated color temperature (CCT) of 5825 K. The above results show that CBH : Eu²⁺ can be used as a promising blue phosphor for WLED. This new method of low-temperature self-reduction can be applied to design and prepare other new types of highly efficient phosphors.

Highly efficient blue-emitting phosphor of Sr[B8O11(OH)4]:Eu2+ prepared by a self-reduction method

A highly efficient blue-emitting phosphor of Sr[B₈O₁₁(OH)₄]:xEu²⁺ was synthesized though a medium-high temperature boric acid melting method by means of a self-reduction mechanism. The quantum yield and color purity of Sr[B₈O₁₁(OH)₄]:6%Eu²⁺ are both as high as 99%. The PL intensity of Sr[B₈O₁₁(OH)₄]:6%Eu²⁺ at 150 °C remains 84% of that at 25 °C.

Mn2+/Mn4+ co-doped LaM1-xAl11-yO19 (M = Mg, Zn) luminescent materials: electronic structure, energy transfer and optical thermometric properties

Dual-emitting manganese ion doped LaM_1-xAl_11-yO₁₉ (M = Mg, Zn) phosphors were prepared by substituting Zn²⁺/Mg²⁺ with Mn²⁺ and replacing Al³⁺ with Mn⁴⁺. The LaM_1-xAl_11-yO₁₉:xMn²⁺,yMn⁴⁺ phosphors show a narrow green emission band of the Mn²⁺ ions at 514 nm and a red emission band of the Mn⁴⁺ ions at 677 nm. In addition, the thermal stability of luminescence shows that the response of Mn²⁺ and Mn⁴⁺ to the temperature is obviously different in LaMAl₁₁O₁₉, implying the potential of the prepared phosphors as optical thermometers. The decay lifetime of Mn⁴⁺ was changed with temperature due to the different fluorescence intensity ratios of Mn²⁺ and Mn⁴⁺, and a dual-mode optical temperature-sensing mechanism was studied in the temperature range of -50-200 °C. The maximum relative sensitivities (S_r) are calculated as 3.22 and 3.13% K^-1, respectively. The unique optical thermometric features demonstrate the application potential of LaMAl₁₁O₁₉:Mn²⁺,Mn⁴⁺ in optical thermometry.

Site occupancy preference of Bi3+ and Bi3+–Eu3+ codoped yttrium galliate phosphors for white LEDs

Novel Y₃GaO₆:Bi³⁺/Eu³⁺ phosphors have been prepared, in which the emission colour of Y₃GaO₆:Bi³⁺ can be adjusted from bluish violet to orange red by changing the Bi³⁺ ion content.

Improved Phase Stability and Enhanced Luminescence of Calcite Phase LuBO3:Ce3+ through Ga3+ Incorporation

The application of LuBO₃:Ce³⁺ (LBO:Ce) crystal as an excellent scintillation material has been limited due to its poor phase stability at high temperature or high pressure, so improving the phase stability is essential for promoting its development. Ga stabilized LuBO₃:Ce³⁺ (LGBO:Ce) is synthesized by solid-state reaction at 1200 °C. Powder X-ray diffraction patterns and Raman spectra at ambient pressure show that all the samples are pure calcite phase. In situ high-pressure synchrotron radiation XRD patterns illustrate that calcite phase LGBO:Ce exhibits more excellent phase stability than that of LBO:Ce under high pressure due to the superior compressibility of the [GaO₆] octahedral unit. The optical band gap of LGBO decreases from 5.58 to 4.64 eV after introducing 10% Ga, which leads to the decreased nonradiative transition and about double luminescence intensity as expected. More interestingly, the charge transition from O^2- to Ce⁴⁺ is observed at about 290 nm in the absorption spectra. The X-ray photoelectron spectroscopy spectra indicate the ratio of Ce⁴⁺/Ce³⁺ increases with increasing concentration of Ga³⁺, which can be attributed to the variation of energy separation between the 4f ground state of Ce³⁺ and the Fermi energy level position. In contrast to the enhancement of PL intensity, the integrated X-ray excited luminescence intensity decreases after Ga³⁺ incorporation attributing to the result of both decreased effective atomic number and ionization energy between 5d₁ level and conduction band. The thermal luminescence spectra show that after the incorporation of Ga³⁺ the oxygen vacancy and intrinsic defects in LBO remain unchanged but that the concentration of oxygen vacancy significantly reduces. The mechanism of Ga³⁺ incorporation on phase stability and luminescence properties of LBO:Ce has been proposed and discussed systematically.

Novel narrow-band blue-emitting Cs3Zn6B9O21:Bi3+ phosphor with superior thermal stability

A novel Bi³⁺-doped CsZn₆B₉O₂₁ blue phosphor shows an extraordinary narrow-band emission with a FWHM of only 50 nm and excellent thermal stability.