Transition Mn Research Articles

A novel Mn4+-doped Li2Mg4TiO7 red-emitting phosphor for warm white light-emitting diodes

To improve the light quality of warm white-LEDs (w-LEDs), novel Mn4+-activated red-emitting phosphors that can be excited efficiently by blue light with yield high performance are highly imperative. Here, we report a Mn4+-doped Li2Mg4TiO7 (LMT) phosphor prepared via a traditional high-temperature reaction method. The crystal structure and luminescent properties of the LMT:Mn4+ phosphors are studied. An excitation band centered at 470 nm, matches well with the commercial blue LED chips. Upon blue light excitation, a broadband red emssion located at 673 nm due to d-d transitions of Mn4+ is observed. The optimum doping concentration of Mn4+ is determined to be x = 0.08 %. The optimized red-emitting phosphor LMT:Mn4+ attains a photoluminescence quantum yield (PLQY) of 40.0 % and a good thermal resistance (ΔE = 0.43 eV). The combination of the as-obtained red-emitting phosphor, commercially available yellow phosphor, and blue LED chip yields a warm w-LED device, delivering CIE (x, y) = (0.3922, 0.3909), CRI = 70.0 and CCT = 2214 K. Therefore, this work provides a novel LMT:Mn4+ phosphor as a potential red component for warm w-LEDs.

Spectroscopic properties and luminescence of the lithium tetraborate glasses co-doped with manganese and europium

High quality Li2B4O7:Mn,Eu glasses containing 1.0 mol.% MnO2 and Eu2O3 were prepared and investigated by XRD, EPR and optical spectroscopy techniques. Obtained data analysis shows that Mn is incorporated into the glass network as Mn2+ and Mn3+. Parameters of observed Mn2+ EPR signals in the Li2B4O7:Mn,Eu glasses were determined. Optical absorption spectrum of the studied glasses consists of broad band at 464 nm corresponding to the 5Eg(D) → 5T2g(D) transition of Mn3+ (3d4) ions and few narrow weak bands of the Eu3+ (4f6) ions. Emission spectra of the Li2B4O7:Mn,Eu glasses in orange-red region exhibit several sharp bands corresponding to the 5D0 → 7FJ (J = 0–4) transitions of Eu3+ ions and broad band belonging to the 4T1g(G) → 6A1g(S) transition of Mn2+ (3d5) ions. Comparative discussions were made on the luminescence spectra and decay curves of Mn2+ and Eu3+ ions in the Li2B4O7:Mn,Eu glasses and those in Mn-doped and Eu-doped glasses with the Li2B4O7 basic composition.

Photoluminescence properties of manganese activated calcium tungstate phosphors

This study presents the novel Mn doped CaWO4 nanophosphors as an excellent alternatives of rare earth free materials for display application. The Mn doped CaWO4 phosphor were characterized by various techniques, such as UV–Vis-DRS, Raman, PL analysis. Scheelite type tetragonal structure with space group I41/a has been confirmed. Rietveld analyses confirms the formation of single-phase solid solution. Lattice parameters for Mn free and Mn doped samples were calculated and observed that cell volume decreases after Mn incorporation. FTIR and Raman studies confirm the involvement of functional group and vibrational modes of vibration in the compound. Band gap values are estimated to be in the range of 4.2 to 4.33 eV with Mn doping. Photoluminescence study confirms the strong green emission at 450 and 515 nm (d-d transition in Mn2+) after Mn doping. Also, it was observed that strong emission peak appears ~422 nm is mainly due to the electronic transition, 1 T2 → 1 A1 in [WO4] 2- tetrahedron of CaWO4 host matrices. CIE study confirms that prepared nanophosphor exhibits strong blue colour after Mn incorporation. It can be employed as a potential material for blue phosphors in LEDs applications.

Near‐unity broadband emissive hybrid manganese bromides as highly‐efficient radiation scintillators

AbstractZero‐dimensional (0D) hybrid manganese halides have gained wide attention for the various crystal structures, excellent optical performance and scintillation properties compared with 3D lead halide perovskite nanocrystals. In this work, a new family of 0D hybrid manganese halides of A2MnBr4 (A = BzTPP, Br‐BzTPP, and F‐BzTPP) based on discrete [MnBr4]2− tetrahedral units is reported as highly efficient lead‐free scintillators. Excited by UV or blue light, these hybrids emit bright green light originating from the d–d transition of Mn2+ with near‐unity PLQY (99.5%). Significantly, high PLQY and low self‐absorption render extraordinary radioluminescence properties with the highest light yield of 80,100 photons MeV−1, which reached the climax of present hybrid manganese halides and surpassed most commercial scintillators. The radioluminescence intensity features a linear response to X‐ray doses with a detection limit of 30 nGyair s−1, far lower than the requirement of medical diagnostic (5.5 µGyair s−1). X‐ray imaging demonstrates ultrahigh spatial resolution of 14.06 lp mm−1 and short afterglow of 0.3 ms showcasing promising application prospects in radiography. Overall, we demonstrated new hybrid manganese halides as promising scintillators for advanced applications in X‐ray imaging with multiple superiorities of nontoxicity, facile‐assembly process, high irradiation light yield, excellent resolution, and stability.

Near-infrared reflective Mg0.5Co0.5-xMnxAl2O4 black pigment synthesized by spray pyrolysis: Optimization of composition and calcination temperature

Co/Mn co-substituted MgAl2O4 pigments were spray pyrolysis, and their crystal structure and optical properties were characterized with changing the Co/Mn ratio and synthesis temperature. Regardless of the Co/Mn ratio, the resulting pigments showed spinel structured MgAl2O4 phase without any impurity phase. The synthesized Mg0.5Co0.5Al2O4 and Mg0.5Mn0.5Al2O4 showed a dark blue and brown color due to the visible light absorption by the 4A2(F) → 4T1(P) transition of Co2+ and the d-d transition of Mn2+, respectively. The black colored pigment was achieved by simultaneous substituting Co2+ and Mn2+ in the Mg2+ tetrahedral site in MgAl2O4. The optical band gap of the Mg0.5Co0.5-xMnxAl2O4 pigment decreased linearly from 3.08 eV (x = 0) to 2.46 eV (x = 0.4) as the Mn2+ content increased. As a result, Mg0.5Co0.1Mn0.4Al2O4 uniformly absorbed the entire visible light and had a black color (L* = 28.10, C* = 1.68). In terms of obtaining high near-infrared reflectance and good blackness, the optimal calcination temperature of Mg0.5Co0.1Mn0.4Al2O4 was determined to be 900 °C. The optimized Mg0.5Co0.1Mn0.4Al2O4 black pigment had a good LiDAR reflectance (38 % at 905 nm) and excellent chemical stability, and showed improved heat shielding performance compared to carbon black using in black vehicles.

Structural, vibrational, and optical studies of newly synthesized Yavapaiite-type phases BaSb2/3X1/3(PO4)2 (X = Mn, Co, Cu, Zn)

The synthesis and structural characterization of four newly synthesized phosphates, BaSb2/3X1/3(PO4)2 phases where X represents Mn, Co, Cu, and Zn, are presented here for the first time. These BaSb2/3X1/3(PO4)2 phases, denoted as [BaSbMn], [BaSbCo], [BaSbCu], and [BaSbZn], were prepared by a solid-state reaction at 900 °C in air atmosphere. The crystal structures of these [BaSbX] materials were investigated using Rietveld analysis based on conventional X-ray powder diffraction. The structural analysis revealed that all four compounds are isostructural, exhibiting the Yavapaiite-type structure with a monoclinic C2/m space group. Raman and infrared spectroscopy were employed to elucidate the bonding characteristics within the [BaSbX] phases. UV–vis-NIR spectroscopy provided insights into the electronic properties of the compounds, revealing charge transfer and d-d transitions in Mn2+, Co2+, and Cu2+ ions. In contrast, Zn2+ exhibited full d orbitals. The absorption spectra revealed UV bands indicative of charge transfer, with optical bandgap values spanning from 3.8 eV to 4.6 eV. This range signifies a distinctive semiconducting property inherent in the synthesized materials. Analysis of the Urbach tails revealed the presence of localized states, with lower values indicating higher crystallinity, giving valuable insights into the electronic behavior of the compounds.

Spectroscopic properties and photoluminescence of the Li2B4O7:Mn,Sm glass

The Li2B4O7:Mn,Sm glass containing 1.0 mol.% MnO2 and Sm2O3 were researched by X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and optical spectroscopy methods. The studied glass of high optical quality was obtained by high temperature melting technique. Parameters of the local structure (interatomic distances and coordination numbers) of Li2B4O7:Mn,Sm glass were derived from XRD data analysis. The EPR and optical spectroscopy (absorption, luminescence excitation, emission, decay kinetics) show the presence of Mn2+(3d5) and Mn3+(3d4) impurity ions in the Li2B4O7:Mn,Sm glass. By EPR spectroscopy in the studied glass were identified three types of Mn2+ centres: single Mn2+ (1) centres in the strongly distorted sites (ratio of rhombic and axial constants, |E/D| ≤ 1/3), single Mn2+ (2) centres in the sites with almost cubic symmetry (D ≅ 0, E ≅ 0) as well as Mn2+ pairs and small clusters coupled by magnetic dipolar and exchange interaction, respectively. The Mn2+ EPR spectra parameters in the Li2B4O7:Mn,Sm glass have been determined at T = 295 K. Optical absorption spectrum of the Li2B4O7:Mn,Sm glass contains a very broad intense band peaked at 467 nm belonging to the 5Eg(D) → 5T2g(D) transition of Mn3+ ions and several weak narrow lines corresponding to the 6H5/2 → 6P3/2, 6H5/2 → 6F9/2, 6F7/2, 6F5/2 transitions of Sm3+ (4f5, 6H5/2) ions. Emission spectrum of the Li2B4O7:Mn,Sm glass exhibits a broad band corresponding to the 4T1g(G) → 6A1g(S) transition of Mn2+ ions and three characteristic bands in the yellow-orange-red range belonging to the 4G5/2 → 6H5/2, 6H7/2, 6H9/2 transitions of Sm3+ ions. Photoluminescence spectra (excitation and emission) and decay kinetics of the Mn2+ and Sm3+ ions in the Li2B4O7:Mn,Sm glass are interpreted in comparison with corresponding results for Li2B4O7:Mn and Li2B4O7:Sm glasses. Energy transfer processes Sm3+→Mn2+, Mn3+, and Mn2+→Mn3+ in the studied glass are considered.

Modulation of trap distribution by optimizing Mn2+ doping in CsCdCl3 crystals toward enhanced afterglow performance

Exploring efficient and stable long-persistent luminescence (LPL) materials is of great value for promoting their advanced applications. Here, the metal halide CsCdCl3:Mn2+ crystals with tunable afterglow properties and good stability were grown by a facile solution method. Upon ultraviolet excitation, CsCdCl3:Mn2+ crystals exhibited a bright orange emission at 590 nm from the d–d transition of Mn2+ ions. Mn2+ doping concentrations matter for the LPL performance. By optimizing the doping amount of Mn2+, an enhanced afterglow duration up to 12 000 s was achieved, compared with undoped sample, originating from a trap redistribution. The deep traps in CsCdCl3:0.1Mn2+ crystal that provide little contribution to the LPL at room temperature shifted to shallow levels, thus synergistically enhancing the afterglow intensity and duration. Based on the variable afterglow durations by tuning Mn2+ doping concentrations, a multi-dimensional information storage encryption model was designed. This work gives deep understanding in doping effect on the afterglow and provides examples for the development of multi-dimensional information encryption.

Tuning Ag+ and Mn2+ doping in ZnS:Ag,Mn embedded polymers for flexible white light emitting films

Flexible Light Emitting Diodes are versatile lighting solutions that offer bendable and adaptable illumination possibilities. A soft, flexible white luminescent film (1 mm) shows promise for foldable electroluminescent devices and applications. This film was fabricated using ZnS:Ag and Mn. Under different excitation wavelengths, the phosphors emit blue light due to Ag+ luminescence centers and red light from the d-d transition of Mn2+. The blue emission is greatly suppressed at high Mn2+ doping levels, requiring reduced Ag+ doping in co-doped ZnS:Ag,Mn compared to solo-doped ZnS:Ag samples. By adjusting Ag+ and Mn2+ concentrations, the ZnS:Ag(1%),Mn(0.2%) phosphors show a proper intensity ratio of blue and red emissions, making them a promising candidate for future white light applications.

Scintillation Performance of Mn(II)‐Doped Cs2NaBiCl6 Double Perovskite Nanocrystals for X‐Ray Imaging Applications

AbstractLead‐free halide perovskite‐based X‐ray scintillators with high light yield (LY) and low detection limit (LOD) have become a growing subject of research interest due to their promising application in a wide range of areas, from security to healthcare. Herein, a modified hot injection method is employed to synthesize Mn(II)‐doped Cs2NaBiCl6 double perovskite nanocrystals (DPNCs) and to examine their scintillating properties for application in X‐ray imaging and detection. The Mn(II)‐doped Cs2NaBiCl6 DPNCs exhibit a broad orange photoluminescence (PL) band at 586 nm with a PL quantum yield of 10.6%, attributed to the 4T2g(4G) → 6A1g(6S) transition of Mn2+. Temperature‐dependent PL and time‐resolved PL spectra of 4.04% Mn(II)‐doped Cs2NaBiCl6 demonstrate that the orange emission intensity initially reaches a maximum and subsequently decreases, while the decay lifetimes monotonically decrease with increasing temperature. This inconsistency can be due to the effect of the [MnCl6]4− octahedra and electron‐phonon coupling at elevated temperatures. Further, 0.05 mm thick Cs2NaBiCl6:4.04%Mn@poly(methyl methacrylate) scintillator film is synthesized with an LY of 28,350 photons MeV−1 and a LOD of 45.2 nGyair s−1. Additionally, this film demonstrates good X‐ray imaging performance with a spatial resolution of 14.76 line pairs (lp) mm−1 and shows exceptional stability under prolonged X‐ray exposure.

Comparative study of optical and dosimetric properties of Mn-doped CaF2

Mn-doped CaF2 has been used as a thermoluminescence detector. On the other hand, dosimetric properties of Mn-doped CaF2 transparent ceramics have not been thoroughly investigated. In this study, transparent ceramics (TC) of Mn-doped CaF2 were fabricated, and the optical and thermally stimulated luminescence (TSL) properties were investigated in comparison with Mn-doped CaF2 single crystal (SC) and opaque ceramics (Cer). The transmittance at 500 nm of the TC, SC, and Cer specimens was 58, 91, and 0%, respectively. All the specimens showed a PL peak at 490 nm with 340, 400, and 450 nm excitations, originating from d-d transitions of Mn2+ ions. The emission and excitation spectra changed with X-ray irradiation, and this phenomenon was attributed to optically stimulated luminescence. All the specimens mainly had a TSL glow peak at 300 °C. The TC specimen exhibited a higher TSL intensity than the SC and Cer specimens.

Highly Efficient and Flexible Scintillation Screen Based on Organic Mn(II) Halide Hybrids toward Planar and Nonplanar X‐Ray Imaging

AbstractThe urgency for cost‐effective, high‐resolution, flexible X‐ray imaging detectors is generating great demand for scintillators with low‐temperature processability, high scintillation yield, and negligible afterglow. X‐ray imaging materials are currently dominated by inorganic scintillators in the form of rigid films and bulk crystals, which have inherent limitations including high‐temperature, complex synthesis, and considerable challenges toward advanced nonplanar imaging. Here, high‐performance and flexible X‐ray scintillators based on novel zero‐dimensional (0D) (BTPP)2MnX4 (BTPP = benzyltriphenylphosphonium; X = Cl, Br) halides are reported. They emit bright green light originating from the 4T1‐6A1 transition of Mn2+ under X‐ray excitation. In particular, (BTPP)2MnBr4 single crystals exhibit excellent air‐ and radiation‐stability, a high scintillation yield of 53 000 photons MeV−1, a low detection limit of 89.9 nGyair s−1, and an ultralow afterglow comparable to commercial Bi4Ge3O12 (BGO) single crystals. Moreover, the (BTPP)2MnCl4@polydimethylsiloxane (PDMS) flexible scintillation screens achieve a high spatial resolution of 14.1 lp mm−1 and realize high‐quality imaging results of nonplanar objects. This study demonstrates that the flexible scintillation screens based on low‐dimensional Mn(II) hybrid halides have significant potential for low‐dose and high‐resolution X‐ray imaging applications.

Metallic (Cum)n+ quantum nanoclusters through the lithium metaphosphate network: Efficient energy transfer to Mn2+ ions for white LED

Metallic (Cum)n+ nanoclusters are superior to their (Aum)n+ and (Agm)n+ counterparts in the aspect of being relatively cheap for wide industrial demands. However, further improvements are still needed, especially in terms of the generation of (Cum)n+ nanoclusters. Herein, (Cum)n+ has been successfully generated with Mn2+ ions into 2.5MnO·47.5Li2O·50P2O5 (MnP), 2.5CuO·47.5Li2O·50P2O5 (CuP) and 2.5MnO·2.5CuO·45Li2O·50P2O5 (CuMnP) matrices. This generation has been demonstrated by XRD, XPS, TEM, SEM, AFM, UV–Vis and PL analyses. MnP displays an amorphous nature with red light emission under an excitation wavelength of 409 nm due to the 4T1(G)→6A1(S) transition of Mn2+ ions. CuP and CuMnP exhibit the formation of spherical nanoclusters with a size less than 10 nm. These nanoclusters are attributed to (Cum)n+, which exhibit tunable emission from blue to white to red light as the excitation wavelength changes from 270 to 360 nm. When MnP, CuP and CuMnP are subjected to 380 °C for 4, 1 and 1 h, respectively, the LiPO3 crystalline phase has evolved. This is associated with the reduction of (Cum)n+ to plasmonic (Cu°)n nanoparticles, and therefore crystallization-induced photoluminescence weakening. This demonstrates that the lithium metaphosphate glassy matrix provides an efficient emission as compared to the corresponding LiPO3 crystalline phase. Overall, in the CuMnP matrix, there is an efficient energy transfer from (Cum)n+ to Mn2+ as the 1Eg excited level of (Cum)n+ is higher than the 4A1/4E energy levels of Mn2+ ions. This synergistic Mn2+/(Cum)n+ combination has resulted in the generation of a rare earth-free platform promised for white LED applications.

Scalable Synthesis of Lead‐Free Tetramethylammonium Manganese Halides for Highly Efficient Backlight Displays

AbstractLead‐free halides have emerged as clean candidates for lighting and display applications because of their superior optoelectronic properties and environmental friendliness. As for the commercialization, the simple synthetic process, scaled production, low‐cost, and excellent performance are the upmost factors. In this work, lead‐free tetramethylammonium manganese halides are quantitatively synthesized using a mechanochemical approach, in which [(CH3)4N]2MnCl4 powders show green emission with a photoluminescence quantum yield (PLQY) of 21% and (CH3)4NMnCl3 powders possess red emission with a PLQY of 51%, arising from the intrinsic 4T1(4G) → 6A1(6S) d‐d transition of Mn2+. To further boost the green emission efficiency, the composition engineering strategies by Br/Cl substitution and excess organic halide compensation are developed, achieving a high PLQY of 98% for the obtained [(CH3)4N]2MnBr4 powders. Furthermore, white light emitting diode (WLED) devices are fabricated by combining green [(CH3)4N]2MnBr4 powders with red (CH3)4NMnCl3 powders or single crystals, which exhibit a high luminous efficacy (98.06 or 142.40 lm W−1), wide color gamut (over 100 % of NTSC in CIE 1931), and good operating stability (maintained above 80% efficiency after 176 h). This work suggests ball‐milling as a mass synthesis method for metal halides and provides a new Mn2+‐based phosphor for white LEDs in backlight display applications.

Methanol‐Induced Crystallization of Chiral Hybrid Manganese (II) Chloride Single Crystals for Achieving Circularly Polarized Luminescence and Second Harmonic Generation

AbstractChiral hybrid Mn (II)‐based halides have attracted great interest in the optoelectronic field due to their low cost, non‐toxicity, abundant structural diversity, and excellent photoluminescence, chiroptical, and nonlinear optical characteristics. Here, chiral hybrids (R/S‐MBA)MnCl3·CH3OH (MBA = C6H5CH(CH3)NH3+) and (R/S‐NPA)Cl·H2O and (R, S‐NPA)Cl (NPA = C10H7CH(CH3)NH3+) single crystals are successfully obtained using methanol (CH3OH) as an induced‐crystallization reagent by slow evaporation method. Interestingly, (R/S‐MBA)MnCl3·CH3OH single crystals with obvious circular dichroism (CD) characteristics exhibit the strong red emission characteristics originating from the d‐d transition of Mn2+ cation, while (R/S‐NPA) Cl·H2O and (R, S‐NPA)Cl exhibit blue emission originating from the organic NPA group. Based on their chiral space group P21 (no.4), (R/S‐MBA)MnCl3·CH3OH single crystals show excellent circularly polarized luminescence (CPL) with a relatively high luminescence dissymmetry factor (glum) value, which is equivalent to that of reported Mn (II)‐based metal halides. Also, (R/S‐NPA)Cl·H2O and (R/S‐MBA)MnCl3·CH3OH exhibit the obvious second harmonic generation (SHG) response. This work not only deepens the understanding of the role of methanol‐induced crystallization in improving the quality and growth habits of Mn (II)‐based halide hybrid single crystals, but also provides guidance for further structural design, crystal growth, and optoelectronic applications of multi‐functional chiral hybrid Mn (II)‐based halide materials.

White‐light emission and red scintillation from Mn2+ ions single‐doped aluminum‐silicate glasses

AbstractA series of Mn2+ single‐doped 0.2Gd2O3‐0.2Al2O3‐0.6SiO2 (GAS: xMn2+) glasses with Si3N4 as reducing agent were prepared. The presence of [SiO4‐x] defects and Mn2+ ions was determined from the absorption and excitation spectra of the glasses. With the increase of Mn2+ concentration, the intensity of blue emission decreases, while the intensity of red emission increases. The color coordinate of GAS: 6Mn2+ glass is (0.264, 0.226). The lifetime of the glasses was tested. Under the monitoring of 440 nm, the fast components (τf) are between 17 and 85 μs, and the slow components (τs) are between 200–650 μs. The former belongs to [SiO4‐x] defects, and the latter is [4E(G), 4A1(G)]→6A1(S) transition of Mn2+ ions. Under the monitoring at 630 nm, the τf are between 110 and 300 μs, and the τs are between 680 and 1220 μs, which are due to 4T1(G)→6A1(S) transition of Mn2+ ions and Mn2+ pairs, respectively. The energy transfer mechanism of [SiO4‐x] defect→Mn2+ ions are explained. The efficient [SiO4‐x] defect →Mn2+ ions energy transfer process was demonstrated by time‐resolved photoluminescence, and the energy transfer efficiency is over 85%. The maximum photoluminescence quantum yield (PL QY) of the glasses can reach 15.87%. The thermal activation energy of the glasses was calculated. In addition, X‐ray excited red luminescence spectra and the mechanism of the glasses were investigated.

INVESTIGATION OF PHOTOLUMINESCENCE OF ZnSxSe1-x AND ZnSxSe1-x:Mn NANOCRYSTALS OBTAINED BY COMBUSTION SYNTHESIS FOR OPTOELECTRIC DEVICES

The photoluminescence spectra of ZnSxSe1-x and ZnSxSe1-x : Mn nanocrystals obtained by combustion synthesis for all compositions with the parameter step x = 0.2 were registered. The movement of the maximum of the integral photoluminescence spectrum in ZnSxSe1-x and ZnSxSe1-x : Mn nanocrystals towards higher energies, depending on the parameter x, was noted. It was noticed that in the range of values x = 0.2÷0.4 there is an abrupt change in the half-width of the integral photoluminescence spectrum in ZnSxSe1-x and ZnSxSe1-x : Mn nanocrystals and the signal intensity; this may be due to the crystal lattice transformation. The parameters of the individual photoluminescence spectra of ZnSxSe1-x : Mn nanocrystals were determined by one experimental measurement based on the Tikhonov method and the derivative spectroscopy method. The nature of the individual photoluminescence bands is discussed. The difference between the integral (sum of individual bands) and experimental spectrum arises from the presence of an additional individual band of low intensity in the experimental spectrum. This individual band is located in the region of E = 2.48 eV and is associated with the electronic transitions in Mn2+ ions in the ZnS lattice.

Single- and dual-band emission CaNb2O6:Mn2+: Synthesis and luminescence properties

Now free rare earth ions doped materials have attracted a lot of attention. In this work, CaNb2O6:Mn2+ with a pure phase is synthesized by solid-state method in the reducing atmosphere. The crystal structure and luminescence properties of host (CaNb2O6) and CaNb2O6:Mn2+ are investigated. Host (CaNb2O6) under excitation ultraviolet (UV) light emits blue light. CaNb2O6:Mn2+ can show tunable emission from blue to white. Under excitation 260 nm, blue emission of CaNb2O6:Mn2+ is observed owing to the 4T1(4G) → 6A1(6S) transition of Mn2+. When the excitation wavelength is 314 nm, CaNb2O6:Mn2+ emits white light due to the 4T1(4G) → 6A1(6S) transition of Mn2+ and the 6A1(6S)4T1(4G) → 6A1(6S)6A1(6S) transition in Mn2+ - Mn2+ dimers. We measure the concentration dependent spectra of CaNb2O6:Mn2+ and make sure the optimal Mn2+ doping concentration (∼0.8 mol%). We infer that the concentration quenching mechanism is the electric multipolar interaction between nearest-neighbor ions. Based on the temperature dependent spectra of CaNb2O6:Mn2+, we came to the conclusion that CaNb2O6:Mn2+ has a good thermal stability. We analyze the concentration and thermal quenching mechanisms and explain the luminous mechanism by the Tanabe-Sugano energy level diagram of Mn2+ ion. This research results provide a framework for creating Mn2+-doped luminescent materials.

Structural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate

AbstractStructural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate were investigated in detail. The complete solid solution of MgP2O6–MnP2O6is confirmed as monoclinic space groupC2/c. The dynamic luminescence was studied by changing the Mn2+content (0–100 mol%) and temperature (10–300 K). There is a good chemical homogeneity in Mg1−xMnxP2O6(x = 0–1.0), which can be supported by the linearly varying cell size and the gradually changing vibration spectrum. However, the optical properties of the solid solution do not show a continuous change trend, that is, an obvious inflection point appeared whenx = 0.5. Mg1−xMnxP2O6(x = 0.1–0.5) shows a dominant O2− → Mn2+charge transfer (CT) absorption in the near UV region and feeble d–d transitions of Mn2+in visible wavelength region. However, Mg1−xMnxP2O6(x = 0.6–1.0) presents a strong d–d absorption transition and nearly disappeared CT band. The changing trend of optical absorption is also maintained in the excitation and emission of the solid solutions. In Mg1−xMnxP2O6(x = 0.1–0.5), (Mn, Mg)O6octahedron has slight distortion, and the effective luminescence only occurs when CT band excitation is used. In contrast, in Mg1−xMnxP2O6(x = 0.6–1.0), (Mn, Mg)O6octahedron is highly distorted, and only excitation at d–d transition produces effective luminescence. This research highlights the critical role of MnO6octahedral distortions in the luminescence properties of Mn2+activators. The research provides a reference for developing optical materials.

Temperature dependent luminescence properties of Mn2+ ions for site preference of NaCa2GeO4F: Mn2+, Fe3+ phosphor

Optical thermometry offers numerous advantages in the field of temperature detection, such as contactless operation, rapid response time, excellent spatial resolution, and wide detection range. Here, a novel optical thermometry strategy based on distinct temperature-dependent luminescence behaviors of Mn2+ ions at distinct crystal sites of NaCa2GeO4F host matrix is explored. NaCa2GeO4F: Mn2+ phosphor exhibits asymmetry broadband emission for the d-d transitions of Mn2+ ions selectively occupying the cation sites. Accordingly, a tunable color from yellow to red is realized thanks to the modulation of site-occupation preference of Mn2+ ions at distinct sites via additionally incorporating Fe3+ ions, and a distinct temperature-dependent luminescence behavior is endowed for the variation of the local environment of Mn2+ ions, which realizes a satisfied relative temperature sensitivity. Our results indicate that the NaCa2GeO4F: Mn2+, Fe3+ phosphor is a potential candidate for optical thermometry.