Energy Transfer Bridge Research Articles

Mn2+/Er3+‐Codoped Cs2AgInCl6 Double Perovskites with Dual Emission and Photochromism Properties for Anti‐Counterfeiting Application

AbstractHighly transparent inorganic photochromic materials have several promising applications, especially for anti‐counterfeiting application. Enriching and enhancing the luminescent properties of perovskite by doping transition metals and rare earth elements into the host is a feasible and attractive route. Codoping of Mn2+ and Er3+ can realize novel anti‐counterfeiting properties with upconversion emission and photochromic ability within a double perovskite structure of Cs2AgInCl6.The Cs2AgInCl6: Mn2+, Er3+ single crystal can be observed in a reversible color variation from yellow to dark violet by implementing under 365, 520 nm illumination or thermal treatment. In addition, the crystal emits red and green light under the excitation of 365 nm ultraviolet and 980 nm laser, respectively. The introduction of Mn2+ endowed Cs2AgInCl6 with photochromic ability, and Mn2+ acted as a bridge for energy transfer from host excitons to Er3+, facilitating emission in the visible region. Er3+ achieve upconversion luminescence in the material through its abundant energy levels and acting synergistically with Mn2+. Herein, the Cs2AgInCl6:Mn2+, Er3+ combines various optical properties and has applications for specific anti‐counterfeiting demands.

Luminescence performance and energy transfer mechanism investigation of RE3+ (Eu3+/Tb3+/Ce3+)-doped Y2O3 phosphors

Tb3+ can serve as a bridge for energy transfer between Ce3+ and Eu3+, overcoming the MMCT quench existing in Eu3+–Ce3+.

Investigation on optical properties of borate Sr3Y2B4O12: Ce/Tb/Sm and its application in wLEDs

Several series of near-ultraviolet (n-UV) convertible white Ce/Tb/Sm-tridoped borate Sr3Y2B4O12 (SYBO) via Ce → Tb → Sm energy transfer (ET) have been successfully obtained by solid-state reaction under reducing atmosphere. The reason why picks Ce/Tb/Sm ions is based on the facts that these lanthanide ions are all extensively used ions in inorganic phosphors and emitting typically in blue, green and red region, respectively, that could be easily mixed and regulated to obtain warm white light within a single phase matrix. The structure, determined from XRD and analysed based on the Rietveld method, shows Y and Sr have 8-fold and 10-, 9- and 8-fold coordination, respectively, and all dopants are more inclined to enter Y sites as compared with Sr sites due to different degrees of radius ratio and charge among the dopants, Y and Sr. The ET mechanism is detailed studied via photoluminescence and decay lifetimes, where the obvious spectral overlap of the PLE for Tb/Sm and PL of Ce with systematic relatively decrease and increase of PL peaks of Ce, Tb/Sm, respectively, clearly indicate the ET occurs. Further, according to spectral studies on codoped (Ce/Tb, Ce/Sm and Tb/Sm) and tridoped phosphors, the Tb acts actually as the ET bridge to better connect Ce and Sm due to ET directly from Ce to Sm is difficult to achieve. Finally, the near-ideal white light from optimal SYBO:Ce/Tb/Sm with color coordinates of (x = 0.328, y = 0.343) and Ra = 86 was observed under n-UV excitation indicates this kind of phosphors could be potentially applied in solid-state lighting.

To achieve tunable-color emission in a novel tri-doped phosphate sulfate phosphor: Tb3+ as the energy transfer bridge

A Tb3+ bridge can overcome the MMCT and realize the sensitization of Eu3+ ions.

Structure of a dimeric photosystem II complex from a cyanobacterium acclimated to far-red light

Photosystem II (PSII) is the water-splitting enzyme central to oxygenic photosynthesis. To drive water oxidation, light is harvested by accessory pigments, mostly chlorophyll (Chl) a molecules, which absorb visible light (400-700nm). Some cyanobacteria facultatively acclimate to shaded environments by altering their photosynthetic machinery to additionally absorb far-red light (FRL, 700-800nm), a process termed far-red light photoacclimation or FaRLiP. During far-red light photoacclimation, FRL-PSII is assembled with FRL-specific isoforms of the subunits PsbA, PsbB, PsbC, PsbD, and PsbH, and some Chl-binding sites contain Chls d or f instead of the usual Chl a. The structure of an apo-FRL-PSII monomer lacking the FRL-specific PsbH subunit has previously been determined, but visualization of the dimeric complex has remained elusive. Here, we report the cryo-EM structure of a dimeric FRL-PSII complex. The site assignments for Chls d and f are consistent with those assigned in the previous apo-FRL-PSII monomeric structure. All sites that bind Chl d or Chl f at high occupancy exhibit a FRL-specific interaction of the formyl moiety of the Chl d or Chl f with the protein environment, which in some cases involves a phenylalanine sidechain. The structure retains the FRL-specific PsbH2 subunit, which appears to alter the energetic landscape of FRL-PSII, redirecting energy transfer from the phycobiliprotein complex to a Chl f molecule bound by PsbB2 that acts as a bridge for energy transfer to the electron transfer chain. Collectively, these observations extend our previous understanding of the structure-function relationship that allows PSII to function using lower energy FRL.

Visible and infrared photoluminescence of Er-doped AlN films: Excitation of Er ions via efficient nonradiative energy transfer from the host level

Aluminum nitride (AlN) is a multifunctional semiconductor. AlN doped with rare earth ions has broad application prospects in monochromatic lighting, color display, laser medium, medical treatment, etc. In this paper, an Er3+-doped AlN film has been prepared by radio frequency magnetron sputtering and characterized by surface morphology, chemical composition and photoluminescence (PL), focusing on the emission mechanism of Er3+ in the AlN host. The films show PL in a wide range of the visible (540, 560 and 668 nm) and near-infrared (816, 869, 985 and 1534 nm) ranges. It has been found a certain energy transfer bridge between Er3+ and AlN defect-related optical transitions. At 532 nm excitation, VAl-ON vacancy-oxygen complex in the AlN host efficiently absorbs photons, then, nonradiative energy transfer (NRET) occurs from the defect levels to the levels of Er3+ since they are in resonance. Since there is a resonance of a donor emission level and an acceptor absorption level, Förster resonance energy transfer (FRET) occurs with the transfer efficiency about 51%. This results in a very strong enhancement of excitation of the 4f related PL. On the contrary, optical excitation at other energies results in a low intensity of the Er3+ PL. As a matter of facts, a strong absorption of the AlN host and the FRET-enabling resonance of donor-acceptor levels allow for a great enhancement of the PL efficiency of Er3+ ions. The results show that the impurity defect state of AlN has an important influence on the Er3+ luminescence efficiency.

Intense 2.85 μm mid-infrared emissions in Yb3+/Ho3+ codoped and Yb3+/Er3+/Ho3+ tridoped TBLL fluorotellurite glasses and their energy transfer mechanism

Yb 3+ /Ho 3+ codoped and Yb 3+ /Er 3+ /Ho 3+ tridoped TeO 2 –BaF 2 –LaF 3 –La 2 O 3 (TBLL) fluorotellurite glasses with low OH − absorption (0.026 cm -1 ), high glass transition temperature (434 °C) and low phonon energy (784 cm -1 ) were prepared. Their mid-infrared fluorescence properties and related energy transfer (ET) mechanism were studied under 980 nm excitation. A strong emission at 2.85 μm was realized in Yb 3+ /Ho 3+ codoped tellurite glass, which was attributed to the high-efficiency ET from Yb 3+ ions to Ho 3+ , and the ET efficiency was 91.1%. Further introduction of Er 3+ ions induced stronger 2.85 μm emission, and the ET efficiency was improved to 96.2%, ascribed to the establishment of more ET channels and Er 3+ ions playing the role of ET bridge between Yb 3+ and Ho 3+ ions. These results indicate that the Yb 3+ /Er 3+ /Ho 3+ tridoped tellurite glass could be a hopeful gain medium material for the ∼3 μm fiber laser.

Realizing broadband spectral conversion in novel Ce3+,Cr3+,Ln3+ (Ln = Yb, Nd, Er) tridoped near-infrared phosphors via multiple energy transfers

The solar spectral converters mainly involve the energy transfer between two codoped ions. Here, we report a series of Ce3+, Cr3+, Ln3+ (Ln = Yb, Nd, Er) tridoped Gd3Sc2Ga3O12 (GSGO) phosphors with improved absorption and increasing near infrared (NIR) emission. We observed the multiple energy transfer behaviors of Cr3+→Ln3+, Ce3+→Ln3+, Ce3+→Cr3+, and Ce3+→Cr3+→Ln3+ in GSGO matrix. When Ce3+ is introduced into the GSGO:Cr3+,Ln3+ phosphors, the energy transfer of Ce3+→Cr3+→Ln3+ has been realized by utilizing the energy transfer bridge of the Cr3+ ion. Consequently, GSGO:Ce3+,Cr3+,Ln3+ can absorb almost all ultraviolet and visible (UV–Vis) light and produce strong NIR light thanks to the synergistic effect of Ce3+→Cr3+→Ln3+, improving the photovoltaic conversion efficiency of c-Si solar cells. Our results show that the prepared GSGO:Ce3+,Cr3+,Ln3+ have the potential application in the solar spectral material for c-Si solar cells. Meanwhile, the strategy of multiple energy transfers gives a new way to design the spectral conversion materials with wider absorption for c-Si solar cells.

Smart design of exquisite multidimensional multilayered sand-clock-like upconversion nanostructures with ultrabright luminescence as efficient luminescence probes for bioimaging application.

Afacile scalable approach ispresented for the rational design of multidimensional, multilayered sand-clock-like UCNPs (denoted as UCCKs) bounded with high index facets, with a tunable Nd3+ content, and without a template or multiple complicated reaction steps. This was achieved using the seed-mediated growth and subsequent longitudinal direction epitaxial growth with the assistance of oleic acid and NH4F. The as-formed UCCKs composed of aninner layer (NaYF4:Yb,Er,Ca), anintermediate layer (NaYF4:Yb,Ca), and anouter layer (NaNdF4:Yb,Ca). The outer shell, enriched with Nd3+ sensitizer, augmented the near-infrared (NIR) photon absorption, whereasthe intermediate shell, enriched with Yb3+, acted as a bridge for energy transfer from Nd3+ to Er3+ emitter in the inner core alongside with precluding any deleterious energy back-transfer from Er3+ or quenching effect from Nd3+. These unique structural and compositional properties of UCCKs endowed the UCL intensity of UCCKs by 22 and 10 times higher than that of hexagonal UCNP core (NaYF4:Yb,Er,Ca) and hexagonal UCNP core-shell (NaYF4:Yb,Er,Ca@NaYF4:Yb,Ca), respectively. Intriguingly, the UCL intensity increased significantly with increasing the content of Nd3+ in the outer shell. The silica-coated UCCKs were used as excellent long-term luminescence probes for the in vitro bioimaging without any noteworthy cytotoxicity. The presented approach may pave the road for controlling the synthesis of multidimensional UCCKs for various applications. Graphical abstract We developed novel multidimensional multilayered sand-clock-like upconversion nanostructures composed of a spherical inner core (NaYF4:Yb,Er,Ca), hexagonal intermediate shell (NaYF4:Yb,Ca) and two up-down outer shell (NaNdF4:Yb,Ca) with controllable Nd3+ as anefficient and safe probe for bioimaging applications without any quenching effect.

Lactic-acid enhanced solvothermal crystallization, color-tunable photoluminescence, and thermal stability of h-LaPO4:Ce3+, Tb3+, Sm3+ nanocrystals

Color-tunable photoluminescence of h-(La0.93−xCe0.05TbxSm0.02)PO4 nanocrystals.

Energy Transfer and Multicolor-Tunable Emissions of Sr3La6(SiO4)6:Ce3+, Tb3+, Eu3+

Multicolor-tunable materials have attracted extensive interest due to their unique advantages in applications of lighting and displays. In this paper, energy transfer from Ce3+ to Tb3+ occurred and the effective energy transfer efficiency (ηETE) of Ce3+-Tb3+ has been calculated to be as high as 36%. To obtain multicolor-tunable emissions, Eu3+ ions were successfully introduced into Ce3+–Tb3+ codoped Sr3La6(SiO4)6 samples. Furthermore, an energy transfer process from Ce3+ to Eu3+ ions has also been demonstrated by an energy transfer bridge of Tb3+. Meanwhile, we achieved the precise adjustment of purple, green, orange and red emissions of Sr3La6(SiO4)6: Ce3+, Tb3+, and Sr3La6(SiO4)6: Ce3+, Tb3+, Eu3+. In addition, Sr3La6(SiO4)6: Ce3+, Tb3+, Eu3+ phosphors exhibited a good thermal stability: their integrated emission intensities at 450 K still kept more than 90% of their initial intensity at room temperature. Therefore, these results might provide a novel multicolor-tunable phosphor for lighting and display application.

Largest Enhancement of Broadband Near-Infrared Emission of Ni2+ in Transparent Nanoglass Ceramics: Using Nd3+ as a Sensitizer and Yb3+ as an Energy-Transfer Bridge

An ultrabroadband near-infrared (NIR) emission of Ni2+ is demonstrated in a highly transparent nanoglass ceramic (nano-GC) containing Ga2O3 nanocrystals with an 808 nm excitation of Nd3+. It is als...

Investigation on structure and optical properties of down-conversion aluminosilicate phosphors CaAl2Si2O8: Ce/Tb/Yb

A series of Ce3+, Tb3+ and Yb3+ tri-doped feldspar CaAl2Si2O8 (CASO) phosphors have been successfully synthesized at ∼ 1350 °C under reducing atmosphere. Optical properties of these phosphors have been investigated as a function of doping concentrations by using fluorescence spectra and decay lifetime analysis in detail. The XRD patterns and structure refinements indicate that the dopants do not change the phase structure of host lattice. For Ce3+/Tb3+/Yb3+ all occupied at Ca2+ sites, charge compensation requires cationic vacancies (VCa//) to maintain electrical neutrality instead of oxygen at interstitial site (Oi2−) because the phosphors were synthesized under reducing atmosphere. The near ultraviolet (n-UV) converted to near-infrared (NIR) emission of the aluminosilicate phosphors have achieved via Ce3+ → Tb3+ → Yb3+ resonant energy transfer (ET), enabling their potential application as down-conversion (DC) converter in Si-based solar cells. The role of Tb3+ is acting as ET bridge to connect Ce3+ and Yb3+ ion pairs. Through adjusting optimal doping concentrations, these NIR DC phosphors can exhibit excitation bands in n-UV region and strong NIR emissions.

Broadband-excited and efficient blue/green/red-emitting Ba2Y5B5O17: Ce3+, Tb3+, Eu3+ phosphors using Tb3+-bridged Ce3+-Eu3+ energy transfer

A series of broadband-excited and color-tunable Ba2Y5B5O17: Ce3+, Tb3+, Eu3+ phosphors were synthesized using Ce3+-Tb3+-Eu3+ energy transfer and their luminescent properties have been comprehensively studied. The Tb3+ ions act as an energy transfer bridge between Ce3+-Eu3+ ion pairs, which can alleviate metal-mediated charge transfer (MMCT) quenching. Therefore, the Eu3+ linear red emission was efficiently sensitized by Ce3+ broad excitation band through a Tb3+ bridge. The emitting color of Ba2Y5B5O17: Ce3+, Tb3+, Eu3+ phosphors could be tuned from blue through green and finally to red with increasing Tb3+/Eu3+ content. By analyzing the variation of the emission intensity and decay lifetime of the sensitizer, it was found that the energy-transfer mechanism of Ce3+-Tb3+ and Tb3+-Eu3+ is dipole-quadrupole and exchange interactions, respectively. The phosphors exhibit high-efficient and blue-green-red color-tunable emission (QE > 40 %) and good thermal stability against temperature quenching (T50 > 473 K).

Enhancing temperature sensing behavior of NaLuF4:Yb3+/Er3 via incorporation of Mn2+ ions resulting in a closed energy transfer

A strategy to improve the sensitivity of NaLuF4:Yb3+/Er3+ is elaborated via incorporation Mn2+ ions, which results a closed energy transfer between Er3+ and Mn2+ ions (4S3/2 (Er3+) → 4T1 (Mn2+) → 4F9/2 (Er3+)). The NaLuF4:Yb3+/Er3+ and NaLuF4:Yb3+/Er3+/Mn2+ phosphors are prepared by a hydrothermal method. Notably, incorporation Mn2+ for NaLuF4:Yb3+/Er3+ phosphor rusults in enhancing the red to green intensity ratio, which acts as a bridge for energy transfer between 4S3/2 and 4F9/2 levels of Er3+. The temperature sensing behaviors of two phosphors are investigated in the 295–595 K range using a ratiometric technique under 980 nm excitation. Based on thermally (2H11/2 and 4S3/2) and non-thermally (4F9/2 and 4S3/2) coupled levels of Er3+, the influences of this energy transfer are discussed in detail. The sensitivity of NaLuF4:Yb3+/Er3+ doping with Mn2+ ions based on non-thermally coupled levels is much higher than that without Mn2+ ions based on both thermally and non-thermally coupled levels in the 295–525 K range. The maximum sensitivity is 10.99 × 10−3 K−1 at 295 K for NaLuF4:Yb3+/Er3+/Mn3+ phosphor. These meaning results indicate that incorporation Mn2+ ions in NaLuF4:Yb3+/Er3+ phosphor is an effective method for enhancing sensitivity in the 295–525 K range.

Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808 nm

As alternatives to Yb3+-sensitized up-conversion (UC) materials excited at 980nm, Nd3+-sensitized UC phosphors irradiated by 808nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from 5F5→5I8 and 5F4/5S2→5I8 transitions of Ho3+ appeared in Nd3+/Yb3+/Ho3+ tri-doped NaLa(MoO4)2 through successive energy transfer Nd3+→Yb3+→Ho3+ under 808nm excitation, in which Yb3+ ions were proven to be the energy transfer bridge between Nd3+ and Ho3+ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb3+, pulse width of the excitation laser and the addition of Ce3+ ion, which depends on the different population pathways to the green and red emitting states of Ho3+. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.

A bridge role of Tb3 + in broadband excited Sr3Y(PO4)3:Ce3 +, Tb3 +, Sm3 + phosphors with superior thermal stability

In this work, we report on a comprehensive study about the bridge role of Tb3+ in broadband excited Sr3Y(PO4)3:Ce3+, Tb3+, Sm3+ phosphors. With Tb3+ acting as an energy transfer bridge, Ce3+→(Tb3+)n→Sm3+ energy transfer process was utilized to circumvent Ce3+-Sm3+ metal-metal charge transfer (MMCT) quenching in Sr3Y(PO4)3 host. Sm3+ was efficiently sensitized by the broad absorption band (4f1→5d1 transition) of Ce3+ in near-ultraviolet spectral region. The color tones of Sr3Y(PO4)3:Ce3+, yTb3+, zSm3+ phosphors were tuned from blue through green and finally to orange with increasing Tb3+/Sm3+ doping concentration. Furthermore, energy transfer mechanisms from Ce3+ to Tb3+ (dipole-dipole mechanism) and Tb3+ to Sm3+ (exchange interaction) as well as the corresponding energy transfer efficiencies (higher than 90%) are systematically investigated. Sr3Y(PO4)3:0.02Ce3+, 0.90Tb3+, 0.02Sm3+ phosphor shows a thermal stability up to 493K, superior to that in analogous reports. The quantum efficiency of Sr3Y(PO4)3:0.02Ce3+, 0.90Tb3+, 0.02Sm3+ phosphor with 315nm excitation was calculated to be 60%.

Utilizing Tb3 + as the energy transfer bridge to connect Eu3 +-Zn2GeO4 host: Realization of efficient Eu3 + red emission

A series of Zn2GeO4:Tb3+, Eu3+ phosphors were prepared by a high temperature solid state reaction technique. The luminescent properties and energy transfer (ET) processes of phosphors were investigated by the X-ray diffraction (XRD), diffuse reflection, thermoluminescence spectra, photoluminescence spectra and decay curves. Under the ultraviolet (UV) radiation, Zn2GeO4 host presents a broad emission band from 350 to 600nm, and the emission band at 430nm is originated from the Vo′, Zni·, VGe and VZn″ native defects. Eu3+ doped Zn2GeO4 has low absorption in the near-UV and blue region, and there is no ET from host to Eu3+ ions. However, the ET from Zn2GeO4 to Eu3+ may be realized by utilizing Tb3+ as the ET bridge to connect Eu3+ and Zn2GeO4 host. Zn2GeO4:Tb3+, Eu3+ exhibits a broad absorption band in the range of 250–450nm, which could be excited by near-UV or blue LED chip. Moreover, the transformation process of crystal structure and defects were investigated by the thermoluminescence and photoluminescence spectra of Zn2GeO4:Tb3+, Eu3+.

Effect of Mn2+ ions on the enhancement red upconversion emission and energy transfer of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics

The effects of Mn2+ ions on the enhancement red upconversion emission intensity of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics were investigated. The ratio I698nm/I478nm significantly increases about ten-fold with the increase of Mn2+ concentrations up to 4.0mol.%. The red upconversion emission of Mn2+/Tm3+/Yb3+ tri-doped transparent glass-ceramics is greatly enhanced, due to constitution of the energy transfer bridge. The upconversion mechanism, the energy transfer and back energy transfer processes between the (1G4→3H6), (3F2→3H6) transitions of Tm3+ ions and the ∣2F7/2, 4T1〉→∣2F7/2, 6A1〉 transitions of Mn2+–Yb3+ dimer were discussed.

Blue upconversion of Tm3+ using Yb3+ as energy transfer bridge under 1532 nm excitation in Er3+, Yb3+, Tm3+ tri-doped CaMoO4

Nano-sized CaMoO4 phosphors tri-doped with Er3+, Yb3+ and Tm3+ ions were successfully synthesized by sol-gel method. Intense blue emission from Tm3+ ions was observed upon excitation of 1532 nm infrared light in Er-Yb-Tm system, while this blue upconversion could not be achieved with the absence of Yb3+ ions in Er-Tm co-doped sample. In order to understand this upconversion process, the upconversion spectra in these samples were investigated, and the possible mechanism was proposed based on experimental results. It showed that two different energy transfer from Er3+ to Tm3+ existed simultaneously in Er-Yb-Tm system, the one-step direct energy transfer from Er3+ to Tm3+, and the two-step Er3+→Yb3+→Tm3+ energy transfer. In particular, the 1G4 state of Tm3+ could only be populated from the 3H4 state by cross-relaxation with an excited Yb3+ ion, producing blue emission of Tm3+. In this upconversion process, Yb3+ ions acted as an energy transfer bridge between Er3+ and Tm3+, which also meant that the upconversion of other rare-earth ions under the excitation of 1532 nm was possible with the presence of Er3+ and Yb3+.