Search

The geometrical and electronic structures of Mn‐doped CaTiO3, CaZrO3, and CaSnO3 deep‐red emission phosphors are investigated both experimentally and theoretically. All the samples are synthesized with solid‐state reaction method by changing the concentration of the doped Mn ions. Crystal structures of the fabricated samples are examined with the powder X‐ray diffraction technique and valence states of the doped Mn ions are determined by measuring the Mn‐L3 X‐ray absorption near‐edge structure (XANES) spectra. Diffuse reflectance spectra are observed to study the change in electronic structures due to the Mn doping. First‐principles calculations are also carried out to investigate geometrical and electronic structures of Mn‐doped CaMO3, in which different types of electron–electron correlation functionals are employed. [ABSTRACT FROM AUTHOR]

Near‐infrared (NIR) phosphor‐converted light‐emitting diodes (pc‐LEDs) have sparked tremendous interest in NIR spectroscopy. However, conventional NIR pc‐LEDs with a narrow full‐width at half‐maximum (FWHM) and single‐emission block the detection scope and detection accuracy for NIR spectroscopy analysis. Herein, a multicenter strategy is developed for the preparation of blue‐light‐excitable Mg2SnO4:Cr3+,Ni2+ phosphors with NIR dual‐emission (λem = 830/1480 nm, total FWHM = 532 nm). Benefiting from the unique NIR dual‐emission, a ratiometric measurement system with a self‐calibration function is established for highly precise and nondestructive detection. For the first time, a good linear relationship with a detection limit of 0.22 wt.% is achieved for quantitative, non‐invasive detection of water/ethanol mixtures in the field of NIR spectroscopy applications. Additionally, a super‐broadband pc‐LED with a NIR output power of 16.1mW@300 mA is fabricated, demonstrating its applications in high‐penetration imaging and anticounterfeiting. These results provide an approach to achieving NIR dual‐emission phosphor, thereby opening a new avenue for exploring ratiometric NIR spectroscopy techniques. [ABSTRACT FROM AUTHOR]

Luminescence of monoclinic lithium metatitanate (Li2TiO3) powders activated with different quantities of Mn4+ is studied in detail. Its strong deep‐red emission arising from the Mn4+ 2Eg → 4A2g spin forbidden transition is centered at around 688 nm and is suitable for luminescence thermometry. Structural and electron paramagnetic resonance analyses show that Mn4+ ions are equally distributed in two almost identical Ti4+ sites in which they are octahedrally coordinated by six oxygen ions. Calculations based on the exchange charge model of the crystal field provided values of Racah parameters (B=760 cm−1, C= 2993 cm−1), crystal‐field splitting Dq= 2043 cm−1, and the nephelauxetic parameter β1=0.9775. The maximal quantum efficiency of 24.1% at room temperature is found for 0.126% Mn4+ concentration. Temperature quenching of emission occurs by a cross‐over via 4T2 excited state of the Mn4+ ions with T1/2=262 K and is quite favorable for the application in the lifetime‐based luminescence thermometry since relative changes in emission decay values are exceptionally‐large (around 3.21% at room temperature). We derived theoretical expressions for the temperature dependence of the absolute and relative sensitivities and discuss the influence of host material properties on lifetime sensitivities. [ABSTRACT FROM AUTHOR]

Abstract: The electronic, structural, and optical properties of 2 red phosphors, Rb2HfF6:Mn4+ and Cs2HfF6:Mn4+, are evaluated using the first‐principles and crystal field theory methods. The calculated trigonal splitting of the Mn4+ orbital triplets perfectly matches the experimental excitation spectra. The structural and electronic properties of the mixed compound RbCsHfF6 are also studied theoretically. In the mixed compound, the inversion center symmetry around the Hf site is removed. This symmetry lowering may result in an increase in the Mn4+2E→4A2 zero phonon line (ZPL) intensity, which is very weak in the 2 end members. This finding may be of interest for increasing the phosphor luminosity. It is believed that such a mechanism of local site symmetry lowering by preparing solid solutions may be used for other systems as well, to gain ZPL intensity and perhaps to minimize thermal losses, eventually leading to improved phosphor materials. [ABSTRACT FROM AUTHOR]

Abstract: The electronic, structural, and optical properties of 2 red phosphors, Rb2HfF6:Mn4+ and Cs2HfF6:Mn4+, are evaluated using the first‐principles and crystal field theory methods. The calculated trigonal splitting of the Mn4+ orbital triplets perfectly matches the experimental excitation spectra. The structural and electronic properties of the mixed compound RbCsHfF6 are also studied theoretically. In the mixed compound, the inversion center symmetry around the Hf site is removed. This symmetry lowering may result in an increase in the Mn4+2E→4A2 zero phonon line (ZPL) intensity, which is very weak in the 2 end members. This finding may be of interest for increasing the phosphor luminosity. It is believed that such a mechanism of local site symmetry lowering by preparing solid solutions may be used for other systems as well, to gain ZPL intensity and perhaps to minimize thermal losses, eventually leading to improved phosphor materials. [ABSTRACT FROM AUTHOR]

Structural and thermal stability are two essential conditions in phosphor research, which are related to the structure of the host and the position of 4T 2 energy lever in Mn4+-activated phosphors. Here, Mn4+-activated CaGdAlO 4 phosphor with superior structural stability was synthesized through systematically screening the aluminate family of ABAlO 4 (A = Mg, Ca, Sr, Ba; B Sc, Lu, Y, Gd, La). Sr2+ was subsequently introduced to modulate the 4T 2 state level of Mn4+ for achieving better thermal stability in CaGdAlO 4 :Sr2+,Mn4+ phosphor. The luminescence quenching temperature T 1/2 show a parabolic trend with the increasing of Sr2+ dopant in Ca 1-y GdAlO 4 :ySr2+, Mn4+ phosphors, and change from 403 K to 426 K and 387 K in CaGdAlO 4 :Mn4+, Ca 0.4 GdAlO 4 :0.6Sr2+,Mn4+ and SrGdAlO 4 :Mn4+ three samples, respectively. The corresponding crystal-field calculations confirm that a certain amount of Sr2+ doping can improve the 4T 2 state of Mn4+ and obtain better thermal stability in the phosphor. All the samples have deep-red emission located at 712 nm, which matches well with the absorption spectra of green vegetables. This deep-red light accelerate morphological formation and increase vegetable biomass. This work is expected to stimulate more exploration of Mn4+-doped oxide phosphors with better structural and thermal stability for emerging applications of agricultural lighting. [ABSTRACT FROM AUTHOR]

Highlights: [•] The evidences of multisite structure of Ce3+ dopant in LuAG scintillation material. [•] The evidences of the lattice expansion of LuAG under influence of RE antisites. [•] Estimated concentration of antisite defects equals to 1.2% of the Al3+ sites. [ABSTRACT FROM AUTHOR]

First-principles calculations are carried out to study the native point defects and dopants (Ce3+, Sm3+) in Li(Y/Lu)SiO 4 for revealing the mechanism of the optical excitation energy storage properties. The calculated excitation and emission energies, the Stokes shifts as well as the positions of 4 f and 5 d levels of Ce3+ relative to host band edges show great consistent with the experimental results. The calculated formation energies reveal that the Li vacancies (V Li) and the antisite defects Li Y and Y Li (or Li Lu and Lu Li) are always much more energetically favorable than Y or Lu vacancies (V Y or V Lu) and O vacancies (V O) in Li(Y/Lu)SiO 4 under reductive atmospheres. Moreover, according to the calculated charge transition levels of the native point defects and the dopants, the antisite defects Y Li (or Lu Li) and the dopants Sm3+ (Sm Y or Sm Lu) are deemed as electron traps that provide suitable charge transition levels for information storage in Li(Y/Lu)SiO 4. Based on our calculations, a mechanism diagram of charge carrier storage and recombination during irradiation and thermal or optical readout is constructed for the storage phosphors Li(Y/Lu)SiO 4 :Ce3+,Sm3+. • The energy spectrum of Ce3+ ion in Li(Y/Lu)SiO 4 is correctly predicted. • Dominant defects and their trap levels are identified with the calculation. • Mechanism of information storage in Li(Y/Lu)SiO 4 :Ce3+,Sm3+ is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-referenced thermal history forensics is demonstrated with Eu3+:YVO 4 luminescence. • Ratio of Eu3+ 5D 0 →7F 2 and 5D 0 -7F 1 emissions strongly depends on the phosphor size. • Thermal history imaging is demonstrated over the 400 – 900 °C range. • Thermal history reading does not depend on the duration of temperature exposure. We demonstrate the thermal history forensic measurements founded on the emission intensity ratio of Eu3+-doped yttrium vanadate. An increase in phosphor's crystallite size with annealing temperature is observed, causing a significant and permanent increase in the emission intensity and symmetry ratio (ratio of Eu3+ 5D 0 → 7F 1 and 5D 0 → 7F 2 emissions). This ratio is used as a forensic indicator of the maximal temperature to which phosphor was exposed. Additionally, we demonstrated that irreversible change in the symmetry ratio after exposure to high temperatures is insensitive to the exposure time. Finally, it is shown that thermal history readings can be performed at any temperature. The applicative potential of the proposed approach was confirmed in the proof-of-concept experiment on a steel plate covered with phosphor and exposed to high temperatures. [ABSTRACT FROM AUTHOR]

The luminescense properties of Ce3+ ions in Ca 2 BO 3 Cl were studied upon excitation in the 3–20 eV range. It is shown that because of the presence of different charge compensating defects, the various types of centers involving Ce3+ are formed in Ca 2 BO 3 Cl. Based on the results obtained, the values of the crystal field splitting and the centroid shift of the Ce3+ 5d configuration for locally uncompensated Ce3+ centers were determined and compared with those of Ce3+ ions in some other inorganic compounds. The DFT calculations were utilized to study the band structure of Ca 2 BO 3 Cl, the 4f→5d transitions of Ce3+ ions and the intrinsic defects of this compound. The calculated band gap of Ca 2 BO 3 Cl (7.22 eV) is consistent with the experimental value of 7.35 eV, and the 4f→5d transition energies for Ce3+ ions on the two sevenfold coordination sites confirm spectral assignments based on the luminescent measurements. The experimental results and first-principles calculations show that the introduction of Na+ hardly influences the luminescence properties of Ce3+-doped Ca 2 BO 3 Cl. The possible processes occurring in Ca 2 BO 3 Cl:Eu2+, Ce3+ persistent phosphors are also discussed based on the combined theoretical and experimental results. • Several types of Сe3+-related centers are observed. • At low Ce3+ concentrations, locally uncompensated Ce3+ centers prevail. • The calculated band gap of Ca 2 BO 3 Cl agrees with the experimental value of 7.35 eV. • VRBE diagram implies the involvement of the CB in the PersL charging process. [ABSTRACT FROM AUTHOR]

In studying the design of novel phosphors and solid-state laser materials, luminescence with a characteristically long lifetime originates from f - f emissions (infrared, visible and ultraviolet). However, due to high demand for novel luminescence materials which excite in the ultraviolet (UV) and vacuum ultraviolet (VUV) ranges, the interconfigurational f - d transition has been of great interest. In this work, we investigated the 4 f n - 4 f n -15 d transition energy of trivalent lanthanide ions in LiYF 4 and CaF 2 host crystals (LiYF 4 : Ln3+ and CaF 2 : Ln3+) without referring to any empirical parameters. These crystals are considered to be promising fluoride hosts for solid-state laser crystals. LnF 8 5− atomic clusters were built based on the crystal structures of LiYF 4 and CaF 2. The relativistic MO calculations were done using the relativistic Discrete Variational Xα (DV-Xα) algorithm. The relativistic version of discrete variational multi-electron method (DVME) algorithm was used to calculate the multiplet energies. We considered the effect of lattice relaxation by a simple estimation using Shannon's crystal radii. Given that the theoretical transition energies are typically underestimated due to the underestimation of the corresponding effects, the absolute transitional energies have received corrections based on one-electron calculations utilizing the Slater's transition-state technique. The in-depth study indicates that the lattice-relaxation effect does not substantially impact LiYF 4 : Ln3+, but greatly affects the transitional energy of heavy lanthanides doped in CaF 2 from 4 f n - 4 f n -15 d. The energy corrections based on Slater's transition-state method are necessary to improve the accuracy of our calculations. By a combination of these two methods, the transition energies of 4 f n - 4 f n -15 d of LiYF 4 : Ln3+ and CaF 2 : Ln3+ agree very well with the experimental data. This research is important to providing guidance in the search for new lanthanide-based phosphors in UV or VUV regions. [Display omitted] • The 4 f n - 4 f n -15 d transition energies of LiYF 4 :Ln3+ and CaF 2 :Ln3+ have been studied. • Effect of lattice relaxation was simply estimated based on Shannon's crystal radii. • Energy corrections utilizing Slater's transition-state method were considered. • The lattice relaxation greatly affects the transitional energy of heavy CaF 2 :Ln3+. • The energy corrections are necessary to improve the accuracy. [ABSTRACT FROM AUTHOR]

[Display omitted] • A precisely space-separated design strategy of donor-acceptor was proposed. • Intense red emitting borosilicate glass doped with CsPbCl 3 and Mn2+ ion was developed. • The external quantum yield of Mn2+ enhances 9.5 times after codoped with CsPbCl 3. • Only Mn2+ ions that are very close to CsPbCl 3 QDs participate in efficient energy transfer. • Energy coupling mechanism based on space distance/energy transfer rate was proposed. Optical ions doped transparent glasses have attracted more and more attention because of their potential application in photonic applications. Unfortunately, optically active dopants occupy at non-crystalline coordination environment, which leads to their poor luminescence efficiency. Therefore, how to enhance luminescence efficiency of optically active dopants in glasses remains a great challenge. Here, we proposed a precisely space-separated strategy of donor-acceptor and successfully developed an intense red emitting composite borosilicate glass co-doped with CsPbCl 3 quantum dots and Mn2+ ions. By rationally controlling post heat-treatment, CsPbCl 3 QDs acting as donor were uniformly precipitated in glass and Mn2+ ions acting as acceptor are close to CsPbCl 3 QDs but not inside CsPbCl 3 QDs. Benefitted from high absorption efficiency of CsPbCl 3 QDs and efficient energy transfer from CsPbCl 3 QDs to Mn2+ ions in glasses, Mn2+ ions give an intense red broadband emission at 650 nm, 11 times as intense as the one without CsPbCl 3 QDs. The optimal external quantum yield of the as-synthesized composite borosilicate glass is estimated to be 28.5%, 9.5 times as large as 3% for the one without CsPbCl 3 QDs. The precise space-separation and energy transfer rate dependent non-radiative energy coupling mechanism was reasonably proposed to explain how CsPbCl 3 QDs highly absorb energy, efficiently transfer it and finally feeding Mn2+ ion. These results demonstrate that the strategy of using microcrystalline with high absorption efficiency as donor, for instance, CsPbX 3 QDs, to pump optical activator ions as acceptor, for instance, Mn2+ ion in glass may be very promising for developing high luminescent performance ions-doped transparent glasses. [ABSTRACT FROM AUTHOR]