Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications.

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

Rational Design of Nitride Phosphor-In-Glass with Robust Stability and Photoluminescence Performance.

Phosphor-in-glass represents a promising avenue for merging the luminous efficiency of high-quality phosphor and the thermal stability of a glass matrix. Undoubtedly, the glass matrix system and its preparation are pivotal factors in achieving high stability and preserving the original performance of embedded phosphor particles. In contrast to the well-established commercial Y3Al5O12:Ce3+ oxide phosphor, red nitride phosphor, which plays a critical role in high-quality lighting, exhibits greater structural instability during the high-temperature synthesis of inorganic glasses. A telluride glass with a refractive index (RI = 2.15@615 nm) akin to that of nitride phosphor (∼2.19) has been devised, demonstrating high efficiency in photon utilization. The lower glass-transition temperature plays a crucial role in safeguarding phosphor particles against erosion resulting from exposure to high-temperature melts. Phosphor-in-glass retains 93% of the quantum efficiency observed for pure phosphor. The assembled white light-emitting diodes module has precise color tuning capabilities, achieving an optimal color rendering index of 93.7, a luminous efficacy of 80.4 lm/W, and a correlated color temperature of 5850 K. These outcomes hold potential for advancing the realm of inorganic package and high-quality white light illumination.

Defect-induced deep red luminescence of CaGdAlO4-type layered perovskites: multi-cationic sites partial/full substitution and application in pc-LED and plant lighting.

A series of CaGdAlO4-type layered perovskite phosphors showing deep red luminescence (λem = 711 nm, λex = 338 nm) were synthesized via a solid-state reaction. A comprehensive analysis performed via photoluminescence, X-ray photoelectron spectroscopy, thermoluminescence, and fluorescence decay revealed that the deep red luminescence is related to oxygen defects and particularly oxygen interstitials. The defect-related luminescence was effectively regulated through partial substitution of multi-cationic sites (the Ca2+ site with Mg2+, Sr2+, and Ba2+; the Gd3+ site with La3+, Y3+, and Lu3+) and full substitution of Gd3+ with Y3+. Remarkably, a 383.3% stronger luminescence was obtained through partial substitution with Lu3+, and the quantum yield of luminescence reached 28.74%, which is higher than those values of most previously reported self-luminescent systems. A pc-LED device was fabricated using this phosphor, and the device was shown to have potential application in indoor plant cultivation.

Modulation of Bi3+ luminescence from broadband green to broadband deep red in Lu2WO6 by Gd3+ doping and its applications in high color rendering index white LED and near-infrared LED.

Phosphors that exhibit tunable broadband emissions are highly desired in multi-functional LEDs, including pc-WLEDs and pc-NIR LEDs. In this work, broadband emissions were obtained and modulated in the unexpectedly wide spectral range of 517-609 nm for (Lu0.99-xGdxBi0.01)2WO6 phosphors by tuning the Gd3+ content (x = 0-0.99). The effects of Gd3+ doping on phase constituents, particle morphology, crystal structure, and photoluminescence were systematically investigated. Broadband green emission was obtained from Gd3+-free (Lu0.99Bi0.01)2WO6 phosphors (x = 0), whose emission intensity was enhanced by 50% with 5 at% Gd3+ (x = 0.05). The phase transition happened when x > 0.50 and the broadband red-NIR emission was obtained when x = 0.75-0.99. Three luminescence centers were proved to be responsible for the broadband green emissions via crystal structure, spectral fitting and fluorescence decay analysis. A pc-WLED with a high color rendering index (Ra = 91.3), a stable emission color, and a low color temperature (3951 K) was fabricated from the (Lu0.94Gd0.05Bi0.01)2WO6 broadband green phosphor, and an LED device that simultaneously emits high color rendering index white light and NIR light was obtained with the (Gd0.99Bi0.01)2WO6 broadband red-NIR phosphor. Night vision and noninvasive imaging were also demonstrated using the latter LED device.

Systematic Crystallization of NH4Ln(MoO4)2 as a Family of Layered Compounds (Ln = La-Lu and Y), Derivation of Ln2Mo4O15, Crystal Structure, and Photoluminescence.

NH4Ln(MoO4)2 (Ln = La-Lu lanthanide, Y) was crystallized via hydrothermal reaction as a new family of layered materials, from which phase-pure Ln2Mo4O15 was successfully derived via subsequent annealing at 700 °C for the series of Ln elements excluding Ce and Lu. Detailed structure analysis revealed that the ionic size of Ln3+ decisively determined the crystal structure and Mo/Ln coordination for the two families of compounds. NH4Ln(MoO4)2 was analyzed to be orthorhombic (Pbcn space group, no. 60) and monoclinic (P2/c, no. 13) for the larger and smaller Ln3+ of Ln = La-Gd and Ln = Tb-Lu (including Y), respectively, where both the crystal structures have a layered topology featured by the alternative stacking of a [Ln(MoO4)2]- three-tier infinite anionic layer and interlayer NH4+. Four types of crystal structures were found for the Ln2Mo4O15 series, which are monoclinic (P21/a, no. 14) for Ln = La, triclinic (P1̅, no. 2) for Ln = Pr-Sm, triclinic (P1̅, no. 2) for Ln = Eu and Gd, and monoclinic (P21/c, no. 14) for Ln = Tb-Yb (including Y). The photoluminescence of NH4Ln(MoO4)2 (Ln = Eu, Tb) and Ln2Mo4O15:Eu3+ (Ln = La, Gd, Y) was thoroughly investigated in terms of spectral features, quantum efficiency, fluorescence decay, and CIE chromaticity. The thermal stability of luminescence was also studied for Ln2Mo4O15:Eu3+, and the observed charge-transfer excitation components were successfully correlated with the features of the Mo-O polyhedron/unit.

Remarkable structure and luminescence regulation of a Gd2LuAl5O12:Ce garnet phosphor with a Ca2+/Si4+ pair for high-quality w-WLED lighting.

Doping Gd2LuAl5O12:Ce with a Ca2+/Si4+ pair produced a series of Gd1.97-xLuCaxAl5-xSixO12:0.03Ce (x = 0.0-1.2) garnet new phosphors, and remarkable regulation of the crystal structure and Ce3+ luminescence was achieved. Rietveld refinement and spectral analysis revealed that greater incorporation of Ca2+/Si4+ led to a higher lattice rigidity by cell contraction, a narrower bandgap, a longer average bond length/less distortion of the [CeO8] dodecahedron and decreased centroid shift/crystal field splitting of the Ce3+ 5d energy level. A blue-shifted 4f-5d1 transition, a narrower emission band, improved thermal stability of luminescence and a shorter fluorescence lifetime were observed with increasing Ca2+/Si4+ content. Applying the yellowish-green-emitting Gd0.77LuCa1.2Al3.8Si1.2O12:0.03Ce optimal phosphor (x = 1.2), together with a commercial CaAlSiN3:Eu red phosphor, in 450 nm-excited LED lighting produced a low CCT of ∼3625 K and a high CRI/R9 of ∼95.2/94.8, indicating that the phosphor has application potential in high-performance w-WLED.

Site-selective and cooperative doping of Gd3Al5O12:Ce garnets for structural stabilization and warm WLED lighting of low CCT and high CRI.

Synergistic doping of the metastable Gd3Al5O12:Ce garnet with a Ca2+/Hf4+ pair and Sc3+ to form Gd2.97-xCaxHfxScyAl3O12:0.03Ce (x = 0.5-2.0, y = 0.0-1.5, x + y = 2.0) solid solution was conducted for the structural stabilization and photoluminescence manipulation. The site selection of Ca2+/Hf4+/Sc3+ dopants and the effects of doping on the crystal structure, local coordination, band structure and Ce3+ luminescence were revealed in detail with the results of XRD, Rietveld refinement, TEM, and UV-Vis/photoluminescence spectroscopy. A decrease in Ca2+/Hf4+ and an increase in the Sc3+ content were observed to shrink the lattice, widen the bandgap of the garnet host, red-shift the excitation/emission wavelength, broaden the emission band and shorten the fluorescence lifetime of Ce3+. The spectral changes were rationalized by considering the local coordination and crystal field splitting of the Ce3+ 5d energy level. Application of typical Gd0.97Ca2Hf2Al3O12:0.03Ce (x = 2.0, y = 0) cyan and Gd2.47Ca0.5Hf0.5Sc1.5Al3O12:0.03Ce (x = 0.5, y = 1.5) greenish-yellow phosphors in w-WLED lighting produced low correlated color temperatures of ∼3842 and 3514 K, high color rendering indices of ∼88 and 93 and favorable luminous efficacies of ∼32.9 and 14.7 lm/W under the excitation of 395 nm n-UV and 450 nm blue LED chips, respectively.

Doping Pb2+ in LaAlO3 to generate dual emission centers and an optical storage container for visible and near infrared persistent luminescence.

Defects play an important role in luminescence, not only as non-radiative transition centers to decrease the luminescence intensity, but also as useful centers for improving luminescence. Phosphors with unique characteristics can be designed by using effective defects combined with the luminescence center. Here, a novel phosphor of LaAlO3:Pb2+ was synthesized by a solid state reaction. Two kinds of defects, which are and Pb'La, were constructed by incorporation of Pb2+ into LaAlO3. Under UV excitation at 285 nm, the sample outputted a broad cyan emission at 460 nm that is related to the 3P1-1S0 transition of Pb2+, along with a weak near infrared (NIR) emission at 735 nm. However, only NIR emission at 735 nm can be found upon 211 nm excitation. The defect levels of and Pb'La in the band gap are evidenced to be the contributor for the NIR output. Heating the sample resulted in a weakened cyan emission and an enhanced NIR output. Because the defects of and Pb'La also act as the electron and hole traps, the sample outputted cyan and NIR afterglows after removing the irradiation source. Since the optical signal of LaAlO3:Pb2+ is sensitive to the excitation wavelength, temperature, and duration time, the multimodal luminescent phosphor may be used as a potential anti-counterfeiting material.

KLn(MoO4)2 micro/nanocrystals (Ln = La-Lu, Y): systematic hydrothermal crystallization, structure, and the performance of doped Eu3+ for optical thermometry.

Systematic crystallization of KLn(MoO4)2 double molybdate micro/nanocrystals was achieved in this work for the family of lanthanide elements (excluding Pm) and Y via hydrothermal reaction under the optimized conditions of pH = 7, Mo/Ln molar ratio R = 5 and 200 °C, with which the intrinsic influence of lanthanide contraction on phase preference, crystallite morphology (size/shape) and crystal structure was clearly revealed. Extended synthesis also produced KLa1-xEux(MoO4)2 (KLM:xEu) and KY1-yEuy(MoO4)2 (KYM:yEu) red phosphors, and detailed spectral analysis found that the layered structure of orthorhombic KYM allows Eu3+ to have a high quenching content of ∼70 at% (y = 0.7) and higher quantum efficiency and thermal stability of luminescence. Application also indicated that the KYM:0.7Eu optimal phosphor has the potential for optical temperature sensing with the thermally coupled 5D0 and 5D1 energy levels of Eu3+.

Malate-aided selective crystallization and luminescence comparison of tetragonal and monoclinic LaVO4:Eu nanocrystals.

With malate (Mal2-) as a new type of chelate, tetragonal (t-) and monoclinic (m-) structured LaVO4:Eu crystals (∼10-60 nm) were selectively crystallized as nanosquares and nanorods via a hydrothermal reaction at 200 °C for 24 h. The effects of the Mal2-:(La,Eu)3+ molar ratio, solution pH and Eu3+ content on the phase structure and crystal morphology were systematically investigated and elucidated. The competition between OH- and Mal2- toward rare earth ions was discussed to play a critical role in phase selection, and the t-phase can only be fabricated at pH ∼ 6-8 with the assistance of Mal2-. The optimal Eu3+ content for luminescence was determined to be ∼5 at% under the VO43- → Eu3+ energy transfer mechanism. Experimental comparison showed that t-(La0.95Eu0.05)VO4 (λex = 275 nm, λem = 620 nm) emits ∼5.3 times as strong as m-(La0.95Eu0.05)VO4 does (λex = 313 nm, λem = 616 nm), while theoretical analysis revealed that the 5D0 level of Eu3+ has a quantum efficiency of ∼80% for the former and ∼70% for the latter. Besides, the t- and m-(La0.95Eu0.05)VO4 nanocrystal phosphors were analyzed to have fluorescence lifetimes of ∼1.53 ± 0.01 and 2.28 ± 0.01 ms for their 620 and 616 nm red emissions, respectively.

New Mg2+/Ge4+-Stabilized Gd3MgxGexAl5-2xO12:Ce Garnet Phosphor with Orange-Yellow Emission for Warm-White LEDs (x = 2.0-2.5).

By stabilization of the Gd3Al5O12 garnet by replacing 80% or more of Al3+ with Mg2+/Ge4+ pairs, a series of new orange-yellow-emitting Gd3MgxGexAl5-2xO12:Ce (x = 2.0-2.5) phosphors were successfully developed for potential application in warm-white-light-emitting diodes (WLEDs). Rietveld structure refinement proved that Mg2+ first substitutes the octahedral Al3+ ion, followed by the replacement of the tetrahedral Al3+ together with Ge4+. The band structure of the x = 2.0 typical garnet was analyzed via density functional theory (DFT) calculations. The incorporation of an increasing content of Mg2+/Ge4+ was experimentally shown to narrow the band gap and expand the unit cell of the garnet host and blue shift the emission/excitation wavelength and shorten the fluorescence lifetime of Ce3+. The photoluminescence behaviors were rationalized by considering the influence of Mg2+/Ge4+ on the crystal structure, band structure, and local coordination. An LED lamp fabricated by combining the (Gd2.97Ce0.03)Mg2Ge2AlO12 optimal phosphor with a 450 nm-emitting InGaN blue LED chip exhibited a color-rendering index of 71.6, luminous efficacy of 16.1 lm/W, and a low correlated color temperature of 2201 K under a driving current of 20 mA, indicating that phosphor may have potential application in warm WLEDs.

On the role of Zr substitution in structure modification and photoluminescence of Li5+2xLa3(Ta1-xZrx)2O12:Eu garnet phosphors.

Solid-state reaction at 1000 °C produces a series of Li-stuffed Li5+2x(La1-yEuy)3(Ta1-xZrx)2O12 garnet phosphors (x = 0-1, y = 0.05-0.6) that exhibit favorable efficiency and thermal stability for red luminescence under either blue or n-UV light excitation, where the optimal composition was identified to be x = 0.5 and y = 0.4. The concentration quenching of luminescence was determined to occur via electric dipole-dipole interactions. Zr4+ substitution for Ta5+, accompanied by additional Li+ for charge compensation, was found via Rietveld structure refinement and Raman/UV-Vis spectroscopy to profoundly affect the tetrahedral and octahedral occupancies of Li, the symmetry of (La/Eu)O8 dodecahedron, and the bandgap of the host lattice and cation disorder, with which the systematically varying excitation and emission behaviors of Eu3+ were deciphered. The Li6(La0.6Eu0.4)3(Ta0.5Zr0.5)2O12 optimal phosphor showed quantum yields of ∼40 and 48% under 393 and 463 nm excitations, respectively, a fluorescence lifetime of ∼0.66 ms for its main emission at 610 nm, color coordinates of around (0.653, 0.347), and can retain as high as ∼85% of its room-temperature emission intensity at 423 K. The phosphor also exhibited a favorable performance for n-UV excited LED lighting.

A groundbreaking strategy for fabricating YAG:Ce3+ transparent ceramic films via sintering of LRH nanosheets on a sapphire substrate.

Here, we proposed a groundbreaking strategy for fabricating YAG:Ce3+ transparent ceramic films via a novel interface reaction of LRH nanosheets with a sapphire substrate without a tedious process. The incorporation of Gd3+ greatly enhanced the emission intensity of the ceramic film by ∼11.3 times. The prepared transparent ceramic film with a high transmittance of ∼97% is a promising photo-converter for WLEDs.

Upconversion luminescence and favorable temperature sensing performance of eulytite-type Sr3Y(PO4)3:Yb3+/Ln3+ phosphors (Ln=Ho, Er, Tm).

Phase-pure eulytite-type Sr3Y0.88(PO4)3:0.10Yb3+,0.02Ln3+ upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er3+), 657 nm red (Ho3+) and 476 nm blue (Tm3+) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 µs, respectively. It was shown that (1) the Er3+ doped phosphor has a better overall performance of temperature sensing with thermally coupled 2H11/2 and 4S3/2 energy levels, whose maximum absolute (S A) and relative (SR ) sensitivities are ~5.07 × 10-3 K-1 at 523 K and ~1.16% at 298 K, respectively; (2) the Ho3+ doped phosphor shows maximum S A and SR values of ~0.019 K-1 (298-573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of 5F5/(5F4,5S2) and 5I4/5F5, respectively; (3) the Tm3+ doped phosphor has a maximum S A of ~12.74 × 10-3 K-1 at 573 K for the non-thermally coupled 3F2,3/1G4 energy levels and a maximum SR of ~1.74% K-1 at 298 K for the thermally coupled 3F2,3/3H4 levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors.

Morphology Tailoring of ZnWO4 Crystallites/Architectures and Photoluminescence of the Doped RE3+ Ions (RE = Sm, Eu, Tb, and Dy).

Tartrate (Tar2-) was originally employed in this work as a chelating/structure-directing agent for hydrothermal crystallization of ZnWO4, where the decisive roles of Tar2-/Zn2+/WO42- molar ratio, solution pH (7-10), and the use of ethylene glycol (EG) cosolvent in phase/morphology evolution were deciphered in detail. It was unambiguously manifested that Tar2- may remarkably retard the intrinsically preferred [001] growth of ZnWO4, transform 1D nanorods to 0D nanoparticles and then to 2D platelets, and meanwhile induce face-to-face alignment of the platelets to form spheroidal, ellipsoidal and snowflakelike 3D architectures, where the 2D crystallites were revealed to develop via oriented attachment (colattice) of non-(00l) facets. A lower solution pH and excessive WO42- were clearly shown to enhance and offset the effect of Tar2-, which led to ellipsoidal assemblies of substantially larger 2D crystallites and suppressed 2D growth/3D assembly of ZnWO4 crystallites, respectively. With the spheroidal architectures for example, doping ZnWO4 with RE3+ yielded (Zn0.98RE0.02)WO4 phosphors (RE = Sm, Eu, Tb, and Dy, respectively) that show luminescence overlapped from the typical linelike and broad-band (∼350-700 nm) emissions of RE3+ and WO6, respectively. The luminescence color of the sample was found to drift away from the blue corner of the CIE chromaticity diagram with RE3+ doping and to be dependent on the type of RE3+.

Grafting of terbium(iii) complexes onto layered rare-earth hydroxide nanosheets to fabricate novel optical fiber temperature sensors.

Optical sensors of temperature possess the unique advantages of contactless measurement and large-scale imaging. Developments have been rapidly made in optical fiber sensors due to their high sensitivity, short response time, and electromagnetic immunity, and being easy to handle and light weight. Therefore, novel optical sensors of temperature based on optical fibers were fabricated to explore their application in special environments, such as poisonous, sparkless, currentless, and gelid ones. The present study is the first report of successful intercalation of neutral Y(iii) complexes in situ into the gallery of Y/Eu binary layered rare-earth hydroxides by hydrothermal processing without replacing the nitrate ions. The swollen layered rare-earth hydroxides were then exfoliated into ultrathin nanosheets ∼2 nm thick through dispersion in formamide. Grafting of Tb(iii) complexes onto the exfoliated nanosheets yielded novel temperature sensor films <100 nm thick, which exhibited color emissions from green to pink tunable through temperatures ranging from 77 to 360 K under ultraviolet excitation. Due to the highly sensitive and temperature-dependent emission, an optical fiber-based temperature sensor was fabricated by employing these novel allochroic films, which showed luminescence that could reversibly undergo repeated thermocycles. These optical fiber sensors have the potential to open up new fields in material functionalities via nanostructure manipulation and functionalized optical fiber engineering.

Dietary isoflavones or isoflavone-rich food intake and breast cancer risk: A meta-analysis of prospective cohort studies.

BACKGROUND & AIMS: Previous studies implied that dietary isoflavone intake may reduce the risk of developing breast cancer, but some have shown ambiguous results. This study aimed to systematically evaluate and summarize available evidence on the effect dietary isoflavone intake has on the risk of developing breast cancer. METHODS: PubMed, Embase, and the Cochrane Library were searched for prospective cohort studies published through April 2017 that evaluated the effect of dietary isoflavone intake on the development of breast cancer. RESULTS: Sixteen prospective cohort studies, involving 11,169 breast cancer cases and 648,913 participants, were identified and included in our data analysis. The pooled relative risk (RR) of breast cancer was 0.99 for high versus low intake of isoflavones (95% confidence interval [CI], 0.91-1.09; P = 0.876) and 0.99 for moderate versus low intake of isoflavones (95%CI, 0.92-1.05; P = 0.653), with insignificant heterogeneity (P = 0.187 for high versus low, and P = 0.192 for moderate versus low). While a moderate consumption of soy-based foods did not significantly affect breast cancer risk, a high intake of soy-based foods associated with a lower risk of developing breast cancer. Considering specific foods, an increased the risk of developing breast cancer was seen with a moderate intake of formononetin, but no significant associations were found between breast cancer risk and other isoflavone-rich diets. CONCLUSIONS: The present meta-analysis indicates that women with a high dietary intake of soy foods may experience a statistically significant reduction in breast cancer risk. However, moderate formononetin consumption may increase the risk of developing breast cancer.

Zn3Ga2Ge2O10:Cr3+ Uniform Microspheres: Template-Free Synthesis, Tunable Bandgap/Trap Depth, and In Vivo Rechargeable Near-Infrared-Persistent Luminescence.

Near-infrared (NIR) emitting persistent phosphors of Cr3+-doped zinc gallogermanate have emerged for in vivo bioimaging with the advantage of no need for in situ excitation. However, it is challenging to synthesize well-dispersed and uniform spherical particles with high brightness, high resolution, and distinguished NIR long afterglow. In this work, Zn3Ga2Ge2O10:Cr3+ (ZGGC) monospheres were directly synthesized by a facile hydrothermal method with the assistance of citric anions (Cit3-), which emit an NIR emission at ∼696 nm and exhibit excellent NIR-persistent luminescence with rechargeability. Controlled experiments indicated that the shape evolution of the ZGGC product is significantly affected by Cit3-, solution pH, and the duration and temperature of hydrothermal reaction. Furthermore, compositional influence on the crystal structure, bandgap, trap depth, and luminescence characteristics of ZnyGa2Ge2O10-δ:Cr3+ (y = 2.8, 3.0, 3.2) were investigated in detail, which allows us to construct an energy level diagram of the ZGGC host, Cr3+ ions, and electron traps. It was found that the bandgap and conduction-band minimum (CBM) are significantly affected by the Zn content, while the valence-band maximum (VBM) is not. The y = 3.0 sample exhibited the best persistent luminescence, owing to its deepest defects. The ZGGC-NH2 prepared through surface functionalization of ZGGC spheres showed distinguished NIR long afterglow, low toxicity, and great potential for in vitro cell imaging and in vivo bioimaging in the absence of excitation. Moreover, the persistent luminescence signal from the ZGGC-NH2 can be repeated in vivo through in situ recharge with external excitation of a red LED lamp, indicating that the ZGGC-NH2 is suitable for applications in long-term in vivo imaging.

Multi-Color Luminescent m-LaPO4:Ce/Tb Monospheres of High Efficiency via Topotactic Phase Transition and Elucidation of Energy Interaction.

Monoclinic (m-) structured (La0.96- xCe0.04Tb x)PO4 phosphor monospheres ( x = 0-0.12) of excellent dispersion and morphology uniformity were calcined (≥600 °C) from their precipitated precursor spheres (∼2.0 µm) of a hexagonal (h-) structure for efficient and multicolor luminescence. The h → m phase transition, driven by dehydration, was originally proposed to proceed in a topotactic manner, which involves displacement of the RE-O polyhedra (RE: rare-earth) along the a/ b axis and slight expansion of the {010} and {100} interplanar spacings of the hydrated h-phase to form the {120} and {100} planes of the anhydrous m-phase, respectively. Analysis of the energy process involving the optically active Ce3+ and Tb3+ ions found efficient Ce3+ → Tb3+ energy transfer occurring via electric dipole-quadrupole interaction, whose efficiency reached the highest value of ∼44.48% at x = 0.10. The Tb3+ codoped phosphors simultaneously displayed the characteristic emissions of Ce3+ (∼313 nm) and Tb3+ (∼545 nm) upon exciting the Ce3+ ions with 275 nm UV light, with which the emission color was finely tuned from dark blue to green by increasing the Tb3+ content. Fluorescence decay analysis found decreasing and almost constant lifetime values for the Ce3+ and Tb3+ emissions at a higher Tb3+ content, respectively, and the phosphor presented the highest external quantum efficiency of ∼84.67% at x = 0.10. The excellent luminescent performance and morphology uniformity may allow the monospheres to find application in lighting and display technologies.

NaLaW2O7(OH)2(H2O): Crystal Structure and RE3+ Luminescence in the Pristine and Annealed Double Tungstates (RE = Eu, Tb, Sm, and Dy).

Hydrothermal reaction of La(NO3)3 and Na2WO4·2H2O at 100 °C and pH 8 resulted in the formation of new compound NaLaW2O7(OH)2(H2O), as confirmed by the X-ray diffraction results, chemical composition, Fourier transform infrared, thermogravimetric/differential thermal analysis, and transmission electron microscopy analyses. The crystal structure was determined in the triclinic system (space group P1̅), with lattice constants a = 5.8671(2) Å, b = 8.2440(2) Å, and c = 9.0108(3) Å, axis angles α = 93.121(2)°, ß = 75.280(2)°, and γ = 94.379(2)°, and cell volume V = 420.03(2) Å3. The structure contains two-dimensional layers of -(W1O6)-(W1O6)-(W2O6)-(W2O6)-(W1O6)-(W1O6)- and -LaO9-LaO9- chains alternating in the a-b plane, which are linked together through NaO6 octahedral trigonal prisms by edges to form a three-dimensional net. Dehydration of the compound proceeds up to a low temperature of ∼350 °C and results in the formation of technologically important NaLa(WO4)2 double tungstate, which is thus a unique precursor for the latter. Na(La,RE)W2O7(OH)2(H2O) and Na(La,RE)(WO4)2 solid solutions separately doped with the practically important activators for which RE = Eu, Tb, Sm, and Dy were also successfully synthesized and investigated for their structural features and photoluminescence properties, including excitation, emission, quantum yield, emission color, and fluorescence decay kinetics. The compounds were shown to exhibit dominantly strong red (∼616 nm for Eu3+; λex = 395 or 464 nm), green (∼545 nm for Tb3+; λex = 278 or 258 nm), deep red (∼645 nm for Sm3+; λex = 251 nm), and yellow (∼573 nm for Dy3+; λex = 254 nm) emission upon being irradiated with the peak wavelengths of their strongest excitation bands.