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Coprecipitation with rare‐earth nitrate, ammonium sulfate, and ammonium hydroxide produced hydroxide‐type amorphous precursors incorporating sulfate and carbonate anions, from which [(Gd1−xLax)0.99Tb0.01]2O2SO4 and [(Gd1−xLax)0.99Tb0.01]2O2S (x = 0, 0.15, 0.3, 0.5, 0.65, 0.8, and 1) were obtained as two series of nanophosphors by calcination at 950°C in air and hydrogen, respectively. The detailed characterization by X‐ray diffractometer, scanning electron microscopy/transmission electron microscopy, Brunauer–Emmett–Teller, and particle sizing confirmed that solid solutions were directly formed and that the products have small crystallite size, unimodal size distribution, and high specific surface area, revealing the advantages of the synthesis method. Photoluminescence study revealed that La3+ admixture may significantly improve the 545 nm main emission of Tb3+ for both the phosphor series. Furthermore, the 545 nm main emission of [(Gd1−xLax)0.99Tb0.01]2O2SO4 was identified to have an excellent thermal stability, which retained over 90% of its room‐temperature intensity at 150°C (no quenching for Gd2O2SO4:Tb3+). The two series of phosphors were comparatively studied for their excitation and luminescence performances, as a function of temperature and La3+ content, and the results were rationalized by considering bandgap, crystal structure, UV absorption, and the character of chemical bonds. [ABSTRACT FROM AUTHOR]

Near-infrared emitting nano-sized particles of ZnGa2−x(Mg/Si)xO4:Cr3+ (x = 0–0.15, termed as ZGMSO:Cr3+) with persistent luminescence were prepared by sol-gel processing followed by calcination. The samples were tested by XRD, TEM, STEM, SAED, Raman, XPS, UV-Vis-NIR, TL, PLE/PL spectroscopy, and persistent luminescence decay analysis. Equimolar incorporation of Mg2+ and Si4+ ions did not change the spindle structure of ZnGa2O4 seriously. Most Mg2+ ions are more likely to occupy the sites in octahedron, but Si4+ ions are more likely to occupy the sites in tetrahedron in priority. A broader bandgap, up shift of conduction band minimum, and more anti-defects were found at a higher Mg2+/Si4+ doping concentration. ZGMSO:Cr3+ outputs near-infrared emission with a dominated band at 694 nm (2E → 4A2 transition of Cr3+), which can last longer than 48 h after the stoppage of UV irradiation. Mg2+/Si4+ doping contributes to a better near-infrared persistent luminescence, and the strongest and the longest NIR afterglow was observed at x = 0.05, owing to that the x = 0.05 sample has the deepest defects. The synthesized nanoparticles of ZGMSO:Cr3+ not only output intense NIR afterglow but also can be recharged by the red light of LED several times, indicating that they are the potential nano probes for bio imaging in living animals. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recently, study on Cr3+‐doped zinc gallate and zinc gallogermanate persistent phosphors has become a hot topic in persistent luminescence and bio imaging areas, because of their near infrared (NIR) emission and long afterglow. However, regulation of efficient traps and improvement of persistent luminescence through bottom‐up design are the key challenge. Here, we recommend a new paradigm of chemical unit co‐substitution with [Mg2+‐Ge4+] substituting for [Ga3+‐Ga3+] in ZnGa2O4, which contributes to the opposite charged and distorted octahedral defects of MgGa′ and GeGa· in pair around the CrN2 ions. The formed defect clusters of MgGa′‐CrN2‐GeGa·, which are closely related to the trap depth, can be accurately regulated through varying the doping content of Mg2+/Ge4+ in the resulting spinel solid solutions of ZnGa2−x(Mg/Ge)xO4:Cr3+ (x = 0–1.25). Moreover, the defect clusters cannot only store and recharge visible and UV radiations that contributes to the long lasting NIR persistent luminescence but also can enhance the NIR emission intensity at ~695 nm. The persistent luminescence induced by UV light excitation exhibits an improvement at a deeper trap depth, but it follows an opposite law through visible light excitation. The prepared nanoparticles have the advantages of intense NIR emission, long lasting afterglow, and excellent rechargeability for visible/UV radiations, so they are the potential nanoprobes for long‐term bio imaging in living animals. [ABSTRACT FROM AUTHOR]

A series of garnet-structured Li 6 Ca(La 0.99- x Yb x Er 0.01) 2 Nb 2 O 12 (0≤ x ≤0.05) phosphors were originally synthesized and examined for upconversion (UC) luminescence and optical temperature sensing under 978 nm laser excitation. It was identified that the optimal content of Yb3+ sensitizer is x =0.04 for Er3+ emission and the non-thermally coupled 2H 11/2 /4F 9/2 energy levels of Er3+ possess a superior capability of optical thermometry, whose maximum absolute sensitivity (~15.20 × 10−3 K−1 at 523 K) is generally ~1.7-6.1 times the values reported to date for most of other UC systems. The optimal Yb3+ content of Li 6 Ca(La 0.99- x Yb x Er 0.01) 2 Nb 2 O 12 is x =0.04 for Er3+ emission and the non-thermally coupled 2H 11/2 /4F 9/2 Er3+ levels were identified to be superior for optical thermometry, whose maximum absolute sensitivity is generally ~1.7-6.1 times those reported for most of other Yb3+/Er3+ codoped systems. Image, graphical abstract [ABSTRACT FROM AUTHOR]

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 (SA) 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 SA 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 SA 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. Phase-pure eulytite-type Sr3Y0.88(PO4)3:0.10Yb3+,0.02Ln3+ upconversion (UC) phosphors (Ln=Ho, Er, Tm) were synthesized via gel-combustion, whose property and mechanism of UC luminescence and the performance of optical temperature sensing with thermally and/or non-thermally coupled energy levels were thoroughly investigated. [ABSTRACT FROM AUTHOR]

Temperature‐sensitive luminescent materials have aroused great interest for practical applications in optical sensors. Layered rare‐earth hydroxides (LRHs) possess rich interlayer chemistry and adjustable composition; thus, they are the promising candidates for designing functional materials, usually through an ion exchange process. Herein, the intercalation of neutral TbIII complex rather than ion exchange was successfully performed in situ into the gallery of Y/Eu binary LRHs by using a hydrothermal process. Interestingly, the swollen LRHs are chameleon luminophores, exhibiting color emissions from green to pink that were tunable through variations in temperature ranging from 77 to 450 K. Because of the highly sensitive and temperature‐dependent emissions, novel optical temperature sensors for 1D and 2D thermal imaging were fabricated by employing the chameleon luminophores, which displayed luminescence capable of reversibly undergoing repeated thermocycles. The present work opens up new fields in layered inorganic materials. Playing to the gallery: The first intercalation of a neutral TbIII complex is successfully performed in situ into the gallery of layered rare‐earth hydroxides (LRH). Novel optical temperature sensors for 1D and 2D thermal imaging are fabricated by employing the allochroic swollen LRHs, which opens up new fields in layered inorganic materials. [ABSTRACT FROM AUTHOR]

Abstract: Uniform spheres of (Yb0.98RE0.02)PO4 orthophosphate (RE=Ho, Er, and Tm, respectively) were synthesized via a homogeneous precipitation procedure mediated by SO42− anions. The as‐precipitated and 1100°C calcined products were determined via laser‐diffraction particle sizing to have the average diameters of ~2.04 ± 0.67 and 1.80 ± 0.93 μm, respectively. The upconversion luminescence of RE3+ under sensitization by the host Yb3+ was studied for the calcination products under 978 nm laser excitation, and it was found that the emissions are dominated by a red band at ~650 nm for Ho3+ (5F5 → 5I8 transition), similarly strong green (~515‐565 nm, 2H11/2/4S3/2 → 4I15/2 transition) and red (~640‐680 nm, 4F9/2 → 4I15/2 transition) bands for Er3+, and a near‐infrared band at ~800 nm for Tm3+ (3H4 → 3H6 transition). The number of laser photons needed to populate the emitting state was determined by varying the excitation power, and the possible photon reactions leading to the observed upconversion were discussed. [ABSTRACT FROM AUTHOR]

Submicron sized, monodispersed spheres of Mn2+, Yb3+/Er3+ and Mn2+/Yb3+/Er3+ doped α-NaYF4 were easily autoclaved from mixed solutions of the component nitrates and ammonium fluoride (NH4F), in the presence of EDTA-2Na. Detailed characterizations of the resultant phosphors were obtained using XRD, Raman spectroscopy, FE-SEM, HR-TEM, STEM, PLE/PL spectroscopy, and fluorescence decay analysis. Finer structure and better crystal perfection was observed at a higher calcination temperature, and the spherical shape and excellent dispersion of the original particles was retained at temperatures up to 600 °C. Under the 980 nm infrared excitation, the Yb3+/Er3+-doped sample (calcined at 400 °C) exhibits a stronger green emission centered at ∼524 nm (2H11/2→4I15/2 transition of Er3+) and a weaker red emission centered at ∼657 nm (4F9/2→4I15/2 transition of Er3+). A 200 °C increase in the temperature from 400 °C to 600 °C resulted in the dominant red emission originating from the 4F9/2→4I15/2 transition of Er3+, instead of the previously dominant green one. Mn2+ doping induced a remarkable more enhanced intensity at ∼657 nm and ∼667 nm (red emission area) than that at ∼524 nm and ∼546 nm (green emission area), because of the non-radiative energy transfer between Mn2+ and Er3+. However, a poor thermal stability was induced by Mn2+ doping. The observed upconversion luminescence of the samples calcined at 400 °C and 600 °C followed the two photon process and the four photon process, respectively. [ABSTRACT FROM AUTHOR]

The dicarboxylate anions of tartrate (C4H4O62−, Tar2−), malate (C4H4O52−, Mal2−), and succinate (C4H4O42−, Suc2−) were originally used as morphology/structure modifiers in the hydrothermal crystallization of YPO4, and both hexagonal (h-) and tetragonal (t-) structured crystals with multiform morphologies of high uniformity were selectively synthesized. The materials were characterized by the combined techniques of XRD, FE-SEM, TEM, FT-IR, TG, and optical spectroscopy, and the mechanisms of phase/morphology evolution were expatiated. It was clearly shown that Tar2− may induce an inverse phase transformation of YPO4 from the thermodynamically stable tetragonal structure (nanoparticles) to the metastable hexagonal structure (microprisms), and a series of controlled experiments exhibited that the performance of Tar2− was strongly affected by the experimental parameters of Tar2−/PO43−/Y3+ molar ratio, solution pH, hydrothermal temperature, and reaction time. In comparison with Tar2−, Mal2− induced the direct crystallization of h-YPO4 microprismatic crystals while Suc2− restricted the 1-D growth of t-YPO4 nanocrystals. For the samples calcined at 700 °C, the down-conversion photoluminescence of Eu3+ in h-YPO4 and t-YPO4 and the up-conversion luminescence of the (Yb/Er)3+ couple in t-YPO4 were also comparatively studied and elucidated in detail. [ABSTRACT FROM AUTHOR]

Red-emitting (La,Eu)2O2SO4 phosphors have been successfully prepared using the layered hydroxide of (La,Eu)2(OH)4SO4·2H2O as the precursor. The precursor compound was firstly crystallized via hydrothermal reaction (100 °C and pH = 9.0) as well-dispersed nanoplates, followed by dehydration and dehydroxylation in the 400–1200 °C temperature range in ambient air to yield (La,Eu)2O2SO4. The phosphors show intense red emissions originated from the f–f transitions of Eu3+, dominantly peaking at 617 nm, under O–Eu charge transfer excitation at 284 nm. The optimal Eu3+ content was experimentally determined to be 5 at.%, agreeing well with theoretical analysis, and the concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis indicates that a higher calcination temperature or Eu3+ content would decrease the lifetime of the 617 nm emission. [ABSTRACT FROM PUBLISHER]

Through restricting thickness growth by performing coprecipitation at the freezing temperature of ~4 °C, solid-solution nanosheets (up to 5-nm thick) of the Ln(OH)NO· nHO layered hydroxide (Ln = YRE; RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm, respectively) were directly synthesized without performing conventional exfoliation. In situ exchange of the interlayer NO with SO produced a sulfate derivative [Ln(OH)(SO)· nHO] of the same layered structure and two-dimensional crystallite morphology but substantially contracted d basal spacing (from ~0.886 to 0.841 nm). The sulfate derivative was systematically compared against its nitrate parent in terms of crystal structure and phase/morphology evolution upon heating. It is shown that the interlayer SO, owing to its bonding with the hydroxide main layer, significantly raises the decomposition temperature from ~600 to 1000 °C to yield remarkably better dispersed oxide nanopowders via a monoclinic LnOSO intermediate. The resultant (YRE)O nanophosphors were studied for their photoluminescence to show that the emission color, depending on RE, spans a wide range in the Commission Internationale de l'Eclairage (CIE) chromaticity diagram, from blue to deep red via green, yellow, orange, and orange red. [ABSTRACT FROM AUTHOR]

In this paper, YAG:Ce microspheres were fabricated by a laser heating method. The microspheres are polycrystalline. The melting of the YAG:Ce powder due to the extremely high temperature provided by the laser heating may account for the fast synthesis of the transparent YAG:Ce microspheres. Due to the temperature gradient during cooling, equiaxed and columnar grains were found inside the microspheres. The equiaxed grains are always located at the outer part of the spheres where large under-cooling was created. However, columnar grains are always found at the inner part of powder where a steep temperature gradient presented during cooling. The average size of the equiaxied crystallites observed from the SEM images is about 5~\mu\m. The columnar crystallites are about 5~\mu\m wide and 20~\mu\m long. In the luminescence investigation, the optimum concentration of Ce^3+ was found to be 2 at%. Furthermore, transparent spheres of other chemical compositions are also possible to be fabricated by this method, indicating its wide range of potential applications. [ABSTRACT FROM PUBLISHER]

This study presents a facile and green route for the synthesis of (La0.95Eu0.05)2O2S red phosphors of controllable morphologies, with the sulfate-type layered hydroxides of Ln2(OH)4SO4·2H2O (Ln = La and Eu) as a new type of precursor. The technique takes advantage of the fact that the precursor has had the exact Ln:S molar ratio of the targeted phosphor, thus saving the hazardous sulfurization reagents indispensable to traditional synthesis. Controlled hydrothermal processing at 120 °C yielded phase-pure Ln2(OH)4SO4·2H2O crystallites in the form of either nanoplates or microprisms, which can both be converted into Ln2O2S phosphor via a Ln2O2SO4 intermediate upon annealing in flowing H2 at a minimum temperature of ∼ 700 °C. The nanoplates collapse into relatively rounded Ln2O2S particles while the microprisms retain well their initial morphologies at 1 200 °C, thus yielding two types of red phosphors. Photoluminescence excitation (PLE) studies found two distinct charge transfer (CT) excitation bands of O2− → Eu3+ at ∼ 270 nm and S2− → Eu3+ at ∼ 340 nm for the Ln2O2S phosphors, with the latter being stronger and both significantly stronger than the intrinsic intra-f transitions of Eu3+. The two types of phosphors share high similarities in the positions of PLE/PL (photoluminescence) bands and both show the strongest red emission at 627 nm (5D0 → 7F2 transition of Eu3+) under S2− → Eu3+ CT excitation at 340 nm. The PLE/PL intensities show clear dependence on particle morphology and calcination temperature, which were investigated in detail. Fluorescence decay analysis reveals that the 627 nm red emission has a lifetime of ∼ 0.5 ms for both types of the phosphors. [ABSTRACT FROM AUTHOR]

In the arena of advanced anti-counterfeit research, developing a multi-level, anti-counterfeit material with tunable luminescence is a hot topic. However, current research has mainly focused on the visible light signal, despite the fact that near-infrared is also suitable for optical anti-counterfeit applications. The importance of the near-infrared signal is because it is more difficult to observe than the visible light signal. Here, a new, persistent, luminescent, near-infrared material composed of Zn 2+ x Ga 4-2 x Sn x O 8 :0.5%Cr3+ (x = 0-0.4) has been synthesized using the sol-gel method. A new anti-site-like defect [ Zn Ga ′ - Sn Ga. ] appeared after incorporating both Zn2+ and Sn4+, along with an intrinsic, anti-site defect [ Zn Ga ′ - Ga Zn. ]. Specifically, the former and latter defects contributed to the deep and shallow traps, respectively. Introducing Zn2+ and Sn4+ resulted in a significant, two-fold enhancement of the NIR emission intensity. This led to an obvious improvement in its persistent luminescence. In the absence of light irradiation, the NIR emitted light lasted for several hours. If heated, the disappeared NIR signal reappeared and lasted for 10 min. Primarily due to both the shallow and deep traps, the prepared samples exhibited dynamic NIR luminescence behavior. This behavior then contributed to the dynamic display information. Collectively, these results indicate that persistent phosphors have great potential for use in advanced, optical anti-counterfeit materials, owing to their ability to afford higher security. [ABSTRACT FROM AUTHOR]

[Display omitted] • Y 2 Mo 4 O 15 : x Yb3+/ y Ho3+ UC phosphors were converted from a new type of precursor. • The process of phase and morphology evolution was unveiled. • Y 2 Mo 4 O 15 : x Yb3+/ y Ho3+ exhibits strong deep-red (630–670 nm) emission under 978 nm laser pumping. • The optimal contents of Yb3+ and Ho3+ were determined. • The photon process of UC luminescence was explained in detail. Hydrothermal reaction of Y(NO 3) 3 ·6H 2 O and (NH 4) 6 Mo 7 O 24 ·4H 2 O at 180 °C for 24 h was performed in this work via systematically varying the solution pH (4–10) and Mo/Y molar ratio (R, 2–5), which produced a NH 4 Y(MoO 4) 2 ·0.19H 2 O new compound that yielded phase-pure Y 2 Mo 4 O 15 upon calcination at 500–700 °C. The pH/R window for the compound to crystallize was determined to be 6–7/3 and 6–9/4–5. The products were characterized in detail by XRD, FTIR, elemental analysis, SEM, TEM, STEM and TG to understand chemical composition and the courses of phase/morphology evolution. Applying the above synthesis strategy successfully produced Y 2 Mo 4 O 15 : x Yb3+, y Ho3+ phosphors that exhibit strong deep-red (630–670 nm, 5F 5 → 5I 8 transition) and weak green (530–560 nm, 5F 4 /5S 2 → 5I 8) emissions under 978 nm laser pumping, where the optimal Yb3+ and Ho3+ contents were determined to be x = 0.20 for y = 0.01 and y = 0.03 for x = 0.10, respectively. Spectral analysis indicated that the up-conversion luminescence occurred via a two-photon process, with the red/green intensity ratio and also the emission color dependent on Yb3+ and Ho3+ contents, which were explained by considering ground state excitation, energy transfer, non-radiative relaxation and cross relaxation. [ABSTRACT FROM AUTHOR]

High-brightness laser lighting requires high luminous efficacy and high thermal performance of luminescent materials. In this study, we designed and fabricated single-phase YAG:Ce ceramics with differential grain sizes by combining the coarse commercial phosphor and fine powder of precusor. The large YAG:Ce grains mainly contribute to excellent luminescence properties. The small YAG:Ce grains not only change the direction of light propagation to improve the luminous efficiency but also effectively increase the Ce3+ content to improve the absorption of blue light, which significantly further enhance the luminescence properties compared with the second phase in the YAG:Ce-base composite ceramics. The luminescent ceramic with 40 wt% large grains sintered under 1550 °C has the highest luminous efficacy of 398.5 lm/W. Compared with the Al 2 O 3 –YAG:Ce composite ceramic, the single-phase YAG:Ce ceramic effectively increased the absorption of blue light to enhance the luminescence properties without the adverse effects caused by the transverse scattering of light in the Al 2 O 3 phase. After encapsulating the ceramic onto a radiator, a high luminous flux of 7697.6 lm under the blue-laser excitation of 3.0 A (54.6 W) was obtained. These indicated its broad application prospects in high-power solid-state laser lighting. [ABSTRACT FROM AUTHOR]

Long persistent luminescence materials developed to commercial standards are primarily concentrated in the blue and green regions, with only a few in the red region. Red, as one of the three basic colors, can be mixed in various proportions with blue and green to yield various colors. The development of red persistent phosphors has a broader application potential but remains a challenge. A solid-state reaction method was used to synthesize new red persistent luminescent materials of Ba 1- x Sr x Ga 2 O 4 :Sm3+ (x = 0–0.09). In BaGa 2 O 4 , both Sr2+ and Sm3+ preferentially occupy the Ba2+ site rather than the Ga3+ site. When exposed to UV light at 254 nm, the phosphors emit the characteristic red emission of Sm3+ at wavelengths ranging from 500 nm to 750 nm. After removing the UV light source, an intense red afterglow that lasted more than 1400 s was observed. The red afterglow signal reappears after a heating process. Doping Sr2+ reduces the trap depth and improves the red persistent luminescence significantly. Because the escaped electrons from traps compensate for the emission loss of Sm3+ during the heating process, the red phosphors have unimaginably luminescent thermal stability. Thus, the emission intensity at 200 °C is 1.6 times that at room temperature. The prepared red persistent phosphors show multimode luminescence, with the output signal being time and temperature sensitive, indicating that they are potential luminescent materials for anti-counterfeiting applications. Finally, a building-block strategy for advanced anti-counterfeiting applications of dynamic display information is proposed, with red persistent phosphors serving as an important component combined with upconversion phosphors of NaYF 4 :Yb3+, Tm3+, and green persistent phosphors of SrAl 2 O 4 :Eu2+, Dy3+. [ABSTRACT FROM AUTHOR]

Uniform phosphor mono-spheres have received continuously increasing attention owing to their excellent luminescence properties. Submicron/near micron-sized Lu 2 O 3 :Eu mono-spheres were successfully prepared by a facile and modified homogeneous precipitation technique from corresponding single-source precursor of Lu(OH)CO 3 :Eu⋅ n H 2 O, without the assistance of any dispersants. The sizes of the precursor spheres can be tuned in the range of 56–790 nm via controlling the primary particle nucleation and particle growth in the homogeneous precipitation. After calcination at 1000 °C, the synthesized precursor spheres (165–790 nm) were converted to Lu 2 O 3 :Eu (110–630 nm) without changing their original spherical shape and excellent dispersion. The particle size-dependent photoluminescence properties of Lu 2 O 3 :Eu mono-spheres were investigated in detail. Enhanced photoluminescence intensity, shorter lifetime, higher external quantum efficiency and almost the same CIE chromaticity coordinates were observed for a particle size of 480 nm. Moreover, temperature-dependent photoluminescence spectra indicated the obtained phosphor mono-spheres have good thermal stability. [ABSTRACT FROM AUTHOR]

In the case of spark plasma sintered (SPSed) oxides, it is known that carbon contamination and oxygen vacancies are introduced during the sintering process due to the SPS characteristic of a carbon-rich environment. The introduction of carbon contamination and oxygen vacancies had a direct effect on the transmittance, and the annealing process mostly recovered the low transmittance of sintered bodies. It also affected the luminescence characteristics. The luminescence intensity of sintered bodies, which was very low due to carbon contamination and oxygen vacancies, could be dramatically improved through the annealing process. In the specimens with longer holding times during SPS, the grain size was increased, and the porosity was also significantly reduced, resulting in higher intensity improvements. Through the SPS process, the sintered body was effectively densified, and the annealing could compensate for the drawback of SPS and enable better luminescence properties. [ABSTRACT FROM AUTHOR]

[Display omitted] • (Gd 0.95 Eu 0.05) 2 O 2 SO 4 monospheres and nanoplates were selectively synthesized from a new type of precursor. • The mechanism and kinetics of composition/phase/morphology evolution were clarified. • The monosphere phosphor emits ∼ 1.35 times as strong as nanoplates. • The monosphere phosphor has a high thermal stability of luminescence (∼81% at 150 °C) Rare-earth oxysulfates (RE 2 O 2 SO 4) attracted attention for large-capacity oxygen storage, low-temperature magnetism and luminescence, whose preparation mostly involves toxic SO x gases and/or complicated procedures. In the phosphor field, monospheres are preferred for a number of applications due to their better luminescence and high packing density. With the simple reactants of RE(NO 3) 3 , Na 2 CO 3 and (NH 4) 2 SO 4 for hydrothermal reaction, dispersed monospheres and nanoplates were selectively synthesized for the recently discovered RE 2 (OH) 2 CO 3 SO 4 · n H 2 O (RE = Gd 0.95 Eu 0.05 , REOCSH) layered compound precursor, from which RE 2 O 2 SO 4 phosphors mostly retaining their precursor morphologies were facilely derived via calcination in air at 800 °C, without involving SO x. Solution pH was found to decisively determine the chemical composition and crystallization kinetics of the initial precipitate, and the possible mechanisms of phase/morphology evolution during hydrothermal treatment were proposed by comparatively investigating the temperature-course and time-course of REOCSH formation under the typical pH values of 6 and 7. It was revealed that (Gd 0.95 Eu 0.05) 2 O 2 SO 4 monospheres emit ∼1.35 times as strong as nanoplates (λ ex = 257 nm, λ em = 617 nm) and may retain as high as ∼81% of the room-temperature intensity at 150 °C. The phosphor monospheres were also analyzed to have a fluorescence lifetime of ∼1.32 ms at room temperature and an activation energy of ∼0.19 eV for the thermal quenching of luminescence. [ABSTRACT FROM AUTHOR]

A series of well-dispersed (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres, with an average diameter of ∼1.2 μm, have been originally prepared via two-phase interfacial precipitation and subsequent calcination. Characteristics of the as-synthesized and calcination products were investigated by the combined techniques of XRD, FE-SEM, TEM, FT-IR and TG-DSC. Under 275 nm excitation, tuning the emission color from blue (0.17, 0.02) to green (0.30, 0.56) was realized via varying the Tb3+ content and through Ce3+ → Tb3+ energy transfer. The optimal content of Tb3+ was found to be ∼15 at% (x = 0.15), and the energy transfer was determined to occur via electric dipole-dipole interaction. Moreover, both the emissions of Ce3+ and Tb3+ present gradually higher thermal stability with increasing Tb3+ content owing to enhanced energy transfer. The (Ce 0.85 Tb 0.15)PO 4 microspheres, which possess the highest absolute quantum efficiency (∼60.1%) across the series and excellent thermal stability (activation energy for thermal quenching of luminescence: ∼0.312 eV), may potentially serve as a single-phase green phosphor for solid-state lighting and field-emission display. Multi-color luminescent (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres were successfully fabricated via gel/solution interfacial precipitation and subsequent calcination. Image 1 • (Ce 1- x Tb x)PO 4 (x = 0–1) microspheres were obtained via interfacial precipitation. • The formation mechanism of (Ce 1- x Tb x)PO 4 spheres was proposed. • Ce3+.→ Tb3+ energy transfer was analyzed to occur via dipole-dipole interaction • (Ce 0.85 Tb 0.15)PO 4 has favorable thermal stability for Tb3+ luminescence. [ABSTRACT FROM AUTHOR]

Abstract Eulytite-type Ba 3 La 1- x (PO 4) 3 : x Ce3+ (x = 0–0.10) and Ba 3- y La 0.97 (PO 4) 3 :0.03Ce3+, y Mn2+ (y = 0.05–0.30) phosphors were first synthesized via gel-combustion and subsequent calcination in an Ar/H 2 atmosphere at 1250 °C. Photoluminescence properties of the phosphors were thoroughly studied, including excitation, emission, emission color, thermal stability and the process of Ce3+ → Mn2+ energy transfer. The Ba 3 La(PO 4) 3 : x Ce3+, y Mn2+ phosphor series simultaneously exhibited the near-ultraviolet emission of Ce3+ (∼370 nm, 4 f 05 d 1 → 4 f 15 d 0 transition) and the orange-red emission of Mn2+ (∼591–605 nm, 4T 1 → 6A 1 transition) upon exciting the Ce3+ ions with ∼276 nm UV light. Owing to Ce3+ → Mn2+ energy transfer most probably occurring via dipole-dipole interaction, gradually enhanced Mn2+ while weakened Ce3+ emission was resulted at a higher Mn2+ content, with which the emission color can be adjusted from blue through reddish-purple and ultimately to orange red. The efficiency of the energy transfer was analyzed to reach its maximum of ∼43.2% at y = 0.30. It was shown that the Ba 3 La 1- x (PO 4) 3 : x Ce3+ and Ba 3- y La 0.97 (PO 4) 3 :0.03Ce3+, y Mn2+ phosphor series both have favorable thermal stabilities, whose activation energy for thermal quenching of luminescence was calculated to be ∼0.28 ± 0.02 eV for Ce3+ in the former while ∼0.22 ± 0.01 eV for Ce3+ and ∼0.21 ± 0.01 eV for Mn2+ in the latter system. Increasing temperature did not alter the emission wavelength of Ce3+ but gradually blue-shifted that of Mn2+ from ∼602 to 583 nm with increasing temperature from 25 to 200 °C. Graphical abstract Image 1 Highlights • Gel-combustion produced Ce3+ and Ce3+/Mn2+ doped Ba 3 La(PO 4) 3 phosphors. • Photoluminescence properties of the phosphors were thoroughly analyzed. • The mechanism and efficiency of Ce3+.→Mn2+ energy transfer were determined. • Favorable thermal stabilities were demonstrated for the phosphors. [ABSTRACT FROM AUTHOR]

Spherical particles of (Y 1- x Eu x )BO 3 ( x = 0–0.20, ∼0.8–1.5 μm in diameter) have been converted from (Y 1- x Eu x )(B(OH) 4 )CO 3 precursors synthesized via homogenous precipitation processing. Detailed characterizations of the samples were achieved by combined techniques of XRD, Raman, FE-SEM, HR-TEM, PLE/PL, and fluorescence decay analysis. Through homogenous precipitation processing in the absence of EG, orthorhombic (Y,Eu)(B(OH) 4 )CO 3 cubic particles were obtained owing to their crystal habit. Proper EG addition leads to the formation of spherical particles, but nano-sized amorphous particles were resulted from the excessive EG content. Longing reaction time or elevating the reaction temperature induced the appearance of cubic ones. Calcining (Y,Eu)(B(OH) 4 )CO 3 at 700 °C yielded hexagonal structured (Y,Eu)BO 3 phase with the space group of P 6 3 / m , but another hexagonal structured (Y,Eu)BO 3 phase (space group: P 6 3 / mmc ) was obtained with the calcination temperatures of 800–1000 °C. The spherical shape and excellent dispersion of the original particles can be well retained up to 800 °C. Upon UV excitation, the (Y 1- x Eu x )BO 3 ( x = 0–0.20) spheres exhibited a typical Eu 3+ emission with the orange emission at 592 nm from the 5 D 0 - 7 F 1 magnetic dipole transitions of Eu 3+ ions taking the dominant role. Space-group vibrations between in 700 °C-phase and 800–1000 °C phase resulted in the blue shift of CTB center, but they did not significantly affect the lifetimes. A higher Eu content ( x = 0.01–0.10) leaded more Eu 3+ ions occupying the non-centrosymmetric site instead of S 6 one, thus inducing enhanced emission of 5 D 0 → 7 F 2 transition, larger asymmetry factor, and red shift of the CIE chromaticity coordinates. However, the asymmetry factor remains nearly constant with the x value up to 0.20. The fluorescence lifetime is similar (5.3 ± 0.3 ms) up to 8 at% of Eu 3+ , followed by decreases at higher Eu 3+ contents. [ABSTRACT FROM AUTHOR]

Phase-pure (Y 1- x Eu x ) 2 WO 6 ( x = 0.2–0.11) red phosphors (average crystallite size ∼66 nm) in a monoclinic structure have been calcined at 1300 °C from their precursors autoclaved from the mixed solutions of rare-earth nitrate and sodium tungstate dihydrate (Na 2 WO 4 ·2H 2 O) at 180 °C and pH∼10, instead of the commonly adopted pH values of 3–7, without the use of any surfactant. The materials were characterized in detail by the combined techniques of XRD, FT-IR, FE-SEM, TEM, EDS, and optical spectroscopy to reveal (1) the phase structure, morphology, and spatial cation distribution of the hydrothermal product, (2) the course of phase and morphology evolution that leads to the targeted tungstate phosphor, and (3) the effects of Eu 3+ content on photoluminescence properties, including excitation/emission, asymmetry factor of luminescence ( 5 D 0 → 7 F 2 / 5 D 0 → 7 F 1 intensity ratio), fluorescence lifetime, and CIE chromaticity coordinates. Through energy transfer from the [WO 6 ] 6− ligands to Eu 3+ , the (Y 1- x Eu x ) 2 WO 6 phosphors exhibit sharp 5 D 0 → 7 F J ( J = 0–4) emissions upon UV excitation into the O 2- -W 6+ charge transfer band peaked at 327 nm, with the red emission at 611 nm being the most prominent ( 5 D 0 → 7 F 2 transition of Eu 3+ ). The optimal Eu 3+ content was determined to be ∼9 at.% ( x = 0.09), and concentration quenching of luminescence was analyzed to be owing to exchange interaction. The emission color moves closer to the red region in the CIE chromaticity diagram with increasing Eu 3+ doping, while fluorescence lifetime of the 611 nm emission, analyzed to be around 1.05 ± 0.05 ms, shows weak dependence on the Eu 3+ content. [ABSTRACT FROM AUTHOR]

Uniform spheres are highly desired for the fabrication of advanced ceramics and as phosphor for lighting and display. Green emitting (Y 0.95− x Gd x Tb 0.05 ) 2 O 3 phosphor spheres were successfully synthesized in this work via homogeneous precipitation, with particular emphases on size enlargement of the particles and the effects of particle size, Gd 3+ incorporation and calcination on photoluminescence. Ammonium nitrate (NH 4 NO 3 ) was originally used to effectively enlarge the precursor particles from ∼150 ± 10 to 590 ± 43 nm, whose effects were found to tend to saturate at NH 4 NO 3 :rare-earth = 1:1 molar ratio. Size enlargement up to ∼630 ± 57 nm has also been achieved via a self-seeded growth approach. The optimal Gd 3+ content for luminescence was determined to be 2 at% ( x = 0.02) for the phosphors, and the spin-allowed 7 F 6 → 7 D J Tb 3+ excitation at ∼278 nm successively lowers at a higher Gd 3+ content or calcination temperature owing to bandgap narrowing of the host lattice. Intensity of the 543 nm green emission steadily improves with increasing temperature of calcination or particle size, and the lifetime of the 543 nm emission, affected by particle size and calcination, falls in the range of ∼1.75–2.81 ms. The phosphors have similar color coordinates of around (0.32, 0.56), irrespective of the Gd content, particle size, and calcination temperature. [ABSTRACT FROM AUTHOR]

[(Gd 0.8 Lu 0.2 ) 0.9− x Tb 0.1 Eu x ] 3 Al 5 O 12 ( x = 0–0.1) garnet phosphors have been calcined from their coprecipitated carbonate precursors at 1300 °C. Detailed materials characterizations are done via XRD, FE-SEM, BET, particle sizing, PL/PLE, and fluorescence decay analyses. The phosphors, with excellent dispersion and uniform particle size and shape, simultaneously exhibit the characteristic Tb 3+ and Eu 3+ emissions with the strongest peaks located at 545 nm (green) and 592 nm (orange red) under the optimal excitation wavelength of 275 nm, which correspond to the 5 D 4 → 7 F 5 and 5 D 0 → 7 F 1 transitions of Tb 3+ and Eu 3+ , respectively. The emission intensities of both Tb 3+ and Eu 3+ remarkably vary with increasing Eu 3+ incorporation, and, as a consequence, the emission color can be readily tuned from approximately green to orange-red. At the optimal Eu 3+ concentration of x = 0.03, the energy transfer efficiency was calculated to be ∼83.2% and the mechanism of energy transfer was analyzed to be electric dipole–dipole interactions. The processes of energy migration among the optically active Gd 3+ , Tb 3+ , and Eu 3+ ions are discussed in detail. Fluorescence decay analysis found rapidly decreasing lifetime for the Tb 3+ emission, conforming to the Tb 3+ → Eu 3+ energy transfer, and the probability of energy transfer is calculated. The [(Gd 0.8 Lu 0.2 ) 0.9− x Tb 0.1 Eu x ] 3 Al 5 O 12 solid-solutions developed in this work may serve as a new type of phosphor that hopefully meets the requirements of various lighting, optical display, and scintillation applications. [ABSTRACT FROM AUTHOR]

The metastable garnet lattice of Yb/Er co-doped Gd 3 Al 5 O 12 (GdAG:Yb/Er) has been effectively stabilized by doping with significantly smaller Lu 3+ to form (Gd,Lu)AG:Yb/Er solid solutions. The phase-pure (Gd,Lu)AG:Yb/Er garnet particles have been successfully achieved by calcining their respective precursors synthesized via carbonate co-precipitation. Partially replacing Gd 3+ with Lu 3+ up to 50 at% ( x =0.5) not only lowers the temperature of garnet crystallization, but also raises the theoretical density of the material. The resultant [(Gd 1− x Lu x ) 0.948 Yb 0.05 Er 0.002 ]AG ( x =0.1–0.5) powders, with good dispersion and fairly uniform particle morphology, exhibit strong green (~510 to 590 nm, 2 H 11/2 , 4 S 3/2 → 4 I 15/2 transitions of Er 3+ ) and red (~635 to 700 nm, 4 F 9/2 → 4 I 15/2 transition of Er 3+ ) emissions under 978 nm laser excitation. The Lu 3+ incorporation effect on the visible emission color and intensity of Er 3+ , as well as the dependence of emission intensity on pumping power were all discussed in detail. The up-conversion phosphor of Yb/Er codoped (Gd,Lu)AG garnet developed in this work may potentially be used as a new type of luminescent material. [ABSTRACT FROM AUTHOR]

Gd2O2SO4:Eu3+ spherical phosphor was successfully synthesized through a simple hydrothermal synthesis routine from commercially available Gd2(SO4)3·8H2O, Eu2(SO4)3·8H2O and urea as the starting materials. The as-synthesized products were characterized by XRD, SEM, FT-IR, DTA–TG–DTG and photoluminescence (PL) spectra. It is found that the phase and morphologies of the precursors are strongly dependent on m value, namely, the molar ratio of urea to Gd2(SO4)3. The optimal m value is 2. DTA–TG–DTG, FT-IR and XRD analyses show that the optimal precursor is composed of amorphous Gd2(OH)2CO3SO4·H2O phase and can be converted into pure Gd2O2SO4 phase at a temperature higher than 800°C for 2h in air. SEM observation shows that the pure Gd2O2SO4 phosphor particles are spherical in shape and well dispersed, with a particle size range of about 1–3μm. PL spectra reveal that the strongest emission peak for Gd2O2SO4:Eu3+ spherical phosphor is located at 620nm under 270nm light excitation, which corresponds to the 5D0 → 7F2 transition of Eu3+ ions. The quenching concentration of Eu3+ ions is 15mol% and the concentration quenching mechanism is the exchange interaction for the 5D0 → 7F2 transition of Eu3+ ions. [ABSTRACT FROM AUTHOR]

A series of garnet-type Li 6 CaLa 2(1- x) Nb 2 O 12 : x RE phosphors (LCLN: x RE, RE = Pr, Sm, Tb and Dy) were prepared via sol-gel processing and subsequent calcination for the first time, with the course of phase evolution and the characteristics of the LCLN host and RE3+ luminescence being investigated in detail. It was found that ∼900–1000 °C is a suitable temperature for precursor calcination to produce the garnet phase and LCLN has a relatively low phonon energy (∼725 cm−1) and a relatively wide bandgap (∼4.53 eV) for luminescence. The LCLN:0.012Pr, LCLN:0.04Sm, LCLN:0.06 Tb and LCLN:0.06Dy typical phosphors were analyzed to have dominant excitation/emission bands at ∼278/489, 265/614, 268/549 and 264/581 nm, emission colors of white, orange, green and yellowish white, and fluorescence lifetimes of ∼0.43, 0.74, 0.90 and 0.44 ms, respectively. Temperature-dependent photoluminescence found that the four phosphors maintained ∼28, 37, 45 and 56% of their room-temperature intensities at 423 K, with activation energies for thermal quenching of ∼0.37, 0.29, 0.34 and 0.25 eV, respectively. The results demonstrated that the Li-stuffed LCLN garnet could be a suitable host for UV excitable multicolor phosphors. • ∼900–1000 °C is an appropriate temperature for precursor calcination to derive Li 6 CaLa 2 Nb 2 O 12 (LCLN) garnet. • The LCLN host is suitable for luminescence purposes. • The photoluminescence of Pr3+, Sm3+, Tb3+ and Dy3+ activators was comprehensively elaborated in LCLN. • The concentration quenching of Sm3+ luminescence in LCLN is dominantly resulted from electric dipole-dipole interaction. [ABSTRACT FROM AUTHOR]

Abstract: Autoclaving the rare-earth nitrate/NH4OH reaction system under the mild conditions of 120–200°C and pH 6–13 have yielded four types of well-crystallized compounds with their distinctive crystal shapes, including Ln2(OH)5NO3·nH2O (Ln=Y and Eu) layered rare-earth hydroxide (hexagonal platelets), Ln4O(OH)9NO3 oxy-hydroxyl nitrate (hexagonal prisms and microwires), Ln(OH)2.94(NO3)0.06·nH2O hydroxyl nitrate (square nanoplates), and Ln(OH)3 hydroxide (spindle-shaped microrods). The occurrence domains of the compounds are defined. Ammonium nitrate (NH4NO3) as a mineralizer effectively widens the formation domains of the NO3 − containing compounds while leads to larger crystals at the same time (up to 0.3mm). Crystallization mechanisms of the compounds and the effects of NH4NO3 were discussed. Optical properties (PLE/PL) of the four phases were characterized in detail and were interpreted from the different site symmetries of Eu3+. The compounds convert to cubic-structured (Y0.95Eu0.05)2O3 by annealing at 600°C while retaining their original crystal morphologies. The resultant phosphor oxides of diverse particle shapes exhibit differing optical properties, in terms of luminescent intensity, asymmetry factor of luminescence and fluorescence lifetime, and the underlying mechanism was discussed. [Copyright &y& Elsevier]

Abstract: (Y0.95Eu0.05)2O3 red phosphor particles with three distinctive morphologies of submicron spheres (up to 180nm), microflowers (up to 10μm) and microplates (up to 50×10μm) have been converted from their respective precursors autoclaved (100–180°C, 12h) from mixed solutions of the component nitrates and hexamethylenetetramine [(CH2)6N4]. The three types of precursors were found to have the approximate compositions M(OH)CO3·H2O for the sphere (M=Y and Eu), M4O(OH)9NO3 for the flower and M2(CO3)3·3H2O for the plate, and their formation domains were defined. Both X-ray diffraction and photoluminescence analysis indicated that a calcination temperature of ⩾800°C is needed to attain a homogeneous (Y0.95Eu0.05)2O3 solid solution and thus improved luminescence. Morphology-confined crystal growth of (Y0.95Eu0.05)2O3 was observed from the microplates, yielding a significantly higher exposure of the (400) facets at elevated temperature. The three types of phosphors exhibited a substantial morphology-dependent photoluminescence (PL)/photoluminescence excitation (PLE) behavior, but did not differ much in the positions of the PLE/PL bands or in the asymmetry factor [I(5D0 → 7F2)/I(5D0 → 7F1)] of the luminescence. Upon UV excitation into the charge transfer band at ∼240nm the microplates showed the strongest red emission at ∼613nm (the 5D0 → 7F2 transition of Eu3+) at a calcination temperature of 1000°C, whose intensity was ∼2.49 and 1.57 times those of the flowers and spheres, respectively. Fluorescence decay analysis yielded similar lifetimes of ∼1.5±0.1ms for the 613nm emission of the three morphologies, suggesting that the differing luminescence was largely morphology-dependent, rather than defect-dependent. [Copyright &y& Elsevier]

● Multiform (Y 0.95 Eu 0.05)PO 4 crystals were attained via hydrothermal reaction. ● Increasing MA content leads to a tetragonal (t-) to hexagonal (h-) phase transition. ● A higher pH or PO 4 3- content favors the crystallization of t-(Y 0.95 Eu 0.05)PO 4. ● The (Y 0.95 Eu 0.05)PO 4 phosphors showed structure/morphology-dependent luminescence. [Display omitted] With maleic acid (MA) as an original and efficient structure/morphology modifier, tetragonal (t-) and hexagonal (h-) structured (Y 0.95 Eu 0.05)PO 4 nano/microcrystals with the diverse morphologies of nanoparticles, nanospindles, nanosquares, nanodisks and microprisms have been successfully synthesized via hydrothermal reaction at 180 °C for 24 h. The systematic study demonstrated that solution pH, MA/(Y 0.95 Eu 0.05)3+ molar ratio and PO 4 3-/(Y 0.95 Eu 0.05)3+ molar ratio are three crucial factors that synergistically determine phase structure and crystal shape/size of the product, and the underlying mechanisms were proposed. Photoluminescence of the (Y 0.95 Eu 0.05)PO 4 crystals was revealed to be strongly morphology/structure dependent, which was discussed in detail in terms of excitation, emission, asymmetry factor of luminescence, quantum yield, fluorescence decay, emission color and thermal stability. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the synthesis and luminescence properties of rare earth doped BiPO4:Ce,Tb nanorods which were prepared via a solvothermal method. The nanorods are of hexagonal structure and they have intense luminescence. In Ce3+/Tb3+ co-doped nanorods, there is energy transfer from Ce3+ to Tb3+ which enhances the luminescence of Tb3+. These materials may find applications in solid state lighting and radiation detection. [Copyright &y& Elsevier]

Perovskite-type microspheres of LaAlO 3 : x Mn4+, y Ge4+ have been fabricated through thermal decomposition of the amorphous precursors autoclaved from the nitrates and ethylene glycol in the prescence of citric acid. LaAlO 3 : x Mn4+ spheres emit broad and bright near infrared (NIR) emission ranging from 680 nm to 750 nm with the maximum at around 730 nm. The quenching concentration for Mn4+ in LaAlO 3 is found at x = 0.1%. In the absence of light source, the spheres emit intense NIR afterglow for 10 min at room temperature, mainly due to the formation of [Mn Al defects. Doping Ge4+ does not significantly change the morphology, crystal structure, band gap, and thermal stability of LaAlO 3 :Mn4+ sample, but it induces stronger asymmetry of MnO 6 and more isolated Mn4+ ions, which thus contributes to greatly enhanced NIR emission intensity by 260%. Ge4+ ions occupying Al site leads to the formation of positive [Ge Al defects, which are closely related to the trap concentration rather than the trap depth. Incorporation of Ge4+ gives rise to the improved persistent luminescence, and the most intense afterglow is found at y = 0.6%. The spheres exhibit repeatable afterglow by a proper heat processing in the absence of light source, indicating their potential application in optical data storage. Image 1 • Perovskite-type microspheres of LaAlO 3 :Mn4+/Ge4+ were originally synthesized. • Doping Ge4+induced a greatly enhanced NIR emission intensity by 260%. • Incorporation of Ge4+ gave rise to the improved persistent luminescence. • The spheres exhibited repeated illumination by heating without light source. [ABSTRACT FROM AUTHOR]

• Air-calcined TbAG:Eu phosphor exhibits red luminescence of Eu3+ (∼575–725 nm) mostly via Tb3+ → Eu3+ energy transfer. • The optimal Eu3+ content of air-calcined TbAG:Eu is about 3 at.%. • ∼63% of the Eu in (Tb 0.97 Eu 0.03)AG was reduced to Eu2+ by calcination in hydrogen at 1500 °C. • Hydrogen-reduced TbAG:Eu exhibits cyan luminescence, with chromaticity coordinates of around (0.286, 0.381), by Tb3+, Eu3+ and Eu2+. • Forward and backward energy transfer among Tb3+, Eu2+ and Eu3+ was suggested to occur via electron exchange interaction. Calcination of coprecipitated precursors at 1500 °C in air produced (Tb 1- x Eu x) 3 Al 5 O 12 garnet phosphors (x = 0.0025-0.05) that exhibit dominant excitations via 4f8 → 4f75d1 (E 1-4) and 7F 6 → 5D 3,4 transitions of Tb3+ and negligible excitation of Eu3+. Exciting the phosphors with 275 nm light (E 2 transition of Tb3+) produced the typical 5D 0 → 7FJ red emissions of Eu3+. Annealing the x = 0.03 sample in hydrogen at 1500 °C reduced ∼62.8% of Eu3+ to Eu2+ and yielded a cyan phosphor that simultaneously exhibits the luminescence of Eu3+ (red), Tb3+ (green) and Eu2+ (broad-band, 400–725 nm) under 327 nm excitation (E 1 transition of Tb3+). The (Tb 0.97 Eu 0.03)AG optimal phosphors calcined in air and hydrogen were assayed to have external/internal quantum efficiencies (in percentage) of ∼23.2/24.2 and 18.6/23.7, respectively. Luminescence features of the two types of phosphors were investigated in detail, and the energy transfer among Tb3+, Eu2+ and Eu3+ ions was discussed. [ABSTRACT FROM AUTHOR]

• Li 6 CaLa 2 Nb 2 O 12 (GCN) garnet was identified to be a favorable host for efficient red luminescence of Eu3+. • The optimal Eu3+ content is ~35 at.% relative to La3+. • The GCN:Eu phosphor is efficiently excitable with either blue or NUV light. • The GCN:0.35Eu optimal phosphor has an excellent thermal stability and favorably high quantum yield. Li 6 CaLa 2 Nb 2 O 12 garnet is known as an electrolyte for Li+-batteries. The sol–gel processing of this work yielded a series of phase pure Li 6 CaLa 2(1− x) Nb 2 O 12 : x Eu3+ garnet phosphors (LCLNG: x Eu; x = 0–0.40) that are efficiently excitable with either near-ultraviolet (NUV, ~350–400 nm) or blue (~450–475 nm) light to produce dominantly strong 610 nm red emission. Increasing Eu3+ substitution for La3+ (larger x) led to smaller cell constant and lower symmetry of the (La/Ca)O 8 dodecahedron, as revealed via Rietveld structure refinement, and meanwhile narrower bandgap. The excitation/emission behaviors and high quenching concentration of Eu3+ (x = 0.35) were interpreted for the phosphor series by considering bandgap energy, (La/Ca)O 8 distortion and local arrangement of atoms. The LCLNG:0.35Eu optimal phosphor was analyzed to have absolute quantum yields of ~51% (λ ex = 393 nm) and 65% (λ ex = 463 nm), fluorescence lifetime of ~0.70 ms and color coordinates of around (0.65, 0.35) at room temperature and to be able to retain as high as ~85% of its room-temperature intensity at 423 K for the 610 nm emission. Application of LCLNG:0.35Eu further indicated that this phosphor has the potential to be used in NUV-excited LEDs. [ABSTRACT FROM AUTHOR]