Efficient Near-infrared Luminescence Research Articles

Efficient near-infrared luminescence in LiInO2:Cr3+ phosphor for light-emitting-diodes

Broadband near-infrared (NIR) spectroscopy produced by efficient and miniaturized NIR phosphor-converted light-emitting diodes (pc-LEDs) has been utilized in portable and mobile devices to realize a variety of applications such as bio-imaging, food-quality analysis, and night-vision. However, developing blue-light excitable NIR phosphor material with efficient emission around 900 nm remains a great challenge. Herein, an efficient LiInO2:Cr3+ phosphors with an emission peak of 897 nm and a full width at half maximum (FWHM) of 129 nm excited by 468 nm were successfully synthesized under a protective atmosphere. The optimized sample shows a particularly high absorption efficiency (AE = 57.8%) and an excellent internal quantum efficiency (IQE = 42.4%), resulting in a relatively high external quantum efficiency (EQE = 24.5%) compared to the developed phosphors with emission peak around 900 nm. Disappointingly, the emission intensity at 373 K of this material retains only 29.6% of that at room temperature, and the strong electron-phonon-coupling (EPC) effect should be responsible for the relatively poor thermal stability. Thus, this work demonstrated an attempt to develop efficient broadband NIR phosphors for spectroscopy applications, and also performed a comprehensive investigation to understand this material.

Efficient Near-Infrared Luminescence of Self-Assembled Platinum(II) Complexes: From Fundamentals to Applications.

ConspectusDesigning bright and efficient near-infrared (NIR) emitters has drawn much attention due to numerous applications ranging from biological imaging, medical therapy, optical communication, and night-vision devices. However, polyatomic organic and organometallic molecules with energy gaps close to the deep red and NIR regime are subject to dominant nonradiative internal conversion (IC) processes, which drastically reduces the emission intensity and exciton diffusion length of organic materials and hence hampers the optoelectronic performances. To suppress nonradiative IC rates, we suggested two complementary approaches to solve the issues: exciton delocalization and molecular deuteration. First, exciton delocalization efficiently suppresses the molecular reorganization energy through partitioning to all aggregated molecules. According to the IC theory together with the effect of exciton delocalization, the simulated nonradiative rates with the energy gap ΔE = 104 cm-1 decrease by around 104 fold when the exciton delocalization length equals 5 (promoting vibronic frequency ωl = 1500 cm-1). Second, molecular deuterations reduce Franck-Condon vibrational overlaps and vibrational frequencies of promoting modes, which decreases IC rates by 1 order of magnitude in comparison to the rates of nondeuterated molecules under ΔE of 104 cm-1. Although deuteration of molecules has long been attempted to increase emission intensity, the results have been mixed. Here, we provide a robust derivation of the IC theory to demonstrate its validity, especially to emission in the NIR region.The concepts are experimentally verified by the strategic design and synthesis of a class of square-planar Pt(II) complexes, which form crystalline aggregates in vapor deposited thin films. The packing geometries are well characterized by the grazing angle X-ray diffraction (GIXD), showing domino-like packing arrangements with the short ππ separation of 3.4-3.7 Å. Upon photoexcitation, such closely packed assemblies exhibit intense NIR emission maximized in the 740-970 nm region through metal-metal-to-ligand charge transfer (MMLCT) transition with unprecedented photoluminescent quantum yield (PLQY) of 8-82%. To validate the existence of exciton delocalization, we applied time-resolved step-scan Fourier transform UV-vis spectroscopy to probe the exciton delocalization length of Pt(II) aggregates, which is 5-9 molecules (2.1-4.5 nm) assuming that excitons mainly delocalized along the direction of ππ stacking. According to the dependence of delocalization length vs simulated IC rates, we verify that the observed delocalization lengths contribute to the high NIR PLQY of the aggregated Pt(II) complexes. To probe the isotope effect, both partially and completely deuterated Pt(II) complexes were synthesized. For the case of the 970 nm Pt(II) emitter, the vapor deposited films of per-deuterated Pt(II) complexes exhibit the same emission peak as that of the nondeuterated one, whereas PLQY increases ∼50%. To put the fundamental studies into practice, organic light-emitting diodes (OLEDs) were fabricated with a variety of NIR Pt(II) complexes as the emitting layer, showing the outstanding external quantum efficiencies (EQEs) of 2-25% and the remarkable radiances 10-40 W sr-1 m-2 at 740-1002 nm. The prominent device performances not only successfully prove our designed concept but also reach a new milestone for highly efficient NIR OLED devices.This Account thus summarizes our approaches about how to boost the efficiency of the NIR emission of organic molecules from an in-depth fundamental basis, i.e., molecular design, photophysical characterization, and device fabrication. The concept of the exciton delocalization and molecular deuteration may also be applicable to a single molecular system to achieve efficient NIR radiance, which is worth further investigation in the future.

Efficient Near‐Infrared Luminescence in Lanthanide‐Doped Vacancy‐Ordered Double Perovskite Cs2ZrCl6 Phosphors via Te4+ Sensitization

All-inorganic lead-free perovskite-derivative metal halides have shown great promise in optoelectronics, however, it remains challenging to realize efficient near-infrared (NIR) luminescence in these materials. Herein, we report a novel strategy based on Te4+ /Ln3+ (Ln=Er, Nd, and Yb) co-doping to achieve efficient NIR luminescence in vacancy-ordered double perovskite Cs2 ZrCl6 phosphors, which are excitable by a low-cost near-ultraviolet light-emitting diode (LED) chip. Through sensitization by the spin-orbital allowed 1 S0 →3 P1 transition of Te4+ , intense and multi-wavelength NIR luminescence originating from the 4f→4f transitions of Er3+ , Nd3+ , and Yb3+ was acquired, with a quantum yield of 6.1 % for the Er3+ emission. These findings provide a general approach to achieve efficient NIR emission in lead-free metal halides through ns2 -metal and lanthanide ion co-doping, thereby opening up a new avenue for exploring NIR-emitting perovskite derivatives towards versatile applications such as NIR-LEDs and bioimaging.

Efficient Near‐Infrared Luminescence in Lanthanide‐Doped Vacancy‐Ordered Double Perovskite Cs2ZrCl6 Phosphors via Te4+ Sensitization

AbstractAll‐inorganic lead‐free perovskite‐derivative metal halides have shown great promise in optoelectronics, however, it remains challenging to realize efficient near‐infrared (NIR) luminescence in these materials. Herein, we report a novel strategy based on Te4+/Ln3+ (Ln=Er, Nd, and Yb) co‐doping to achieve efficient NIR luminescence in vacancy‐ordered double perovskite Cs2ZrCl6 phosphors, which are excitable by a low‐cost near‐ultraviolet light‐emitting diode (LED) chip. Through sensitization by the spin‐orbital allowed 1S0→3P1 transition of Te4+, intense and multi‐wavelength NIR luminescence originating from the 4f→4f transitions of Er3+, Nd3+, and Yb3+ was acquired, with a quantum yield of 6.1 % for the Er3+ emission. These findings provide a general approach to achieve efficient NIR emission in lead‐free metal halides through ns2‐metal and lanthanide ion co‐doping, thereby opening up a new avenue for exploring NIR‐emitting perovskite derivatives towards versatile applications such as NIR‐LEDs and bioimaging.

Efficient near-infrared luminescence and energy transfer mechanism in Ca3Al2O6: Ce3+, Yb3+ phosphors

Solar cells have been extensively studied as a means of green energy converters in recent decades, especially the silicon solar cells. However, the energy efficiency of crystalline solar cells is very low, which is due to the reason that they have a good absorption in 800–1100 nm region but a bad absorption in 300–500 nm region. Based on this, a series of Ce3+-Yb3+ codoped Ca3Al2O6 samples are synthesized by the conventional solid state method in reduced atmosphere. Energy transfer process from Ce3+ to Yb3+ is affirmed by the characterizations of photoluminescence, photoluminescence excitation spectra and decay curves in different temperatures. The photoluminescence intensity and lifetime of Ce3+ decrease with the increase of Yb3+ content. And as the temperature increases, the energy transfer efficiency increases. These results demonstrated that the near-infrared luminescence from 2F5/2 to 2F7/2 transition of Yb3+ is implemented via a multi-phonon assisted energy transfer process in the Ce3+-Yb3+ ions pair. These phosphors exhibit broadband absorption in the ultraviolet region with efficient near-infrared emission (centering at 976 nm), which has better spectral response for crystalline Si solar cells. The obtained results illustrated that the phosphors have potential applications as spectral conversion materials to enhance the performance of crystalline Si solar cells.

Near-Infrared Luminescence in Trinuclear Mixed-Metal Chalcogenolate Complexes of the Types [M2Ti(EPh)6(PPh3)2] (M = Cu, Ag; E = S, Se) and [Na(thf)3]2[Ti(SPh)6

The optical properties of four new trinuclear chalcogenolato bridged metal complexes [Ag2Ti(SPh)6(PPh3)2], [Na(thf)3]2[Ti(SPh)6], [Cu2Ti(SePh)6(PPh3)2], and [Ag2Ti(SePh)6(PPh3)2] have been investigated by absorption and photoluminescence spectroscopy as well as time-dependent density functional theory (TDDFT) calculations and compared to the results published recently for [Cu2Ti(SPh)6(PPh3)2]. All of these compounds are distinguished by efficient near-infrared luminescence at ∼880-1200 nm in the solid state at low temperatures, which remains quite intense for the copper-titanium complexes at ambient temperature with PL quantum yields of 9.5 and 4.8% at λPL = 1090 and 1240 nm for [Cu2Ti(EPh)6(PPh3)2], E = S, Se, respectively. According to the calculations, a peculiar feature of the lowest-energy electronic transitions in these complexes is their high localization on the metal and chalcogen atoms, with negligible contributions of the "external" ligand groups. Correspondingly, the type of atoms in the M2TiE6 (M = Cu, Ag, Na) core structure determines optical properties such as the absorption and emission wavelengths and PL lifetime.

Flexible, Transparent, and Hazy Cellulose Nanopaper with Efficient Near-Infrared Luminescence Fabricated by 2D Lanthanide (Ln = Nd, Yb, or Er) Metal-Organic-Framework-Grafted Oxidized Cellulose Nanofibrils.

Three-dimensional (3D) bulk materials, such as metal-organic frameworks (MOFs) and inorganic phosphors, show the properties of large backscattering and stress concentration, which result in low mechanical and inferior transmittance when these materials are hydridized with a polymer matrix. Inspired by the "reinforcement" effects of two-dimensional (2D) materials, such as grapheme, C3N4, MoS2, and Mxene, it was interesting to examine a 2D lanthanide (Ln)-based MOF-grafted natural polymer (nanocellulose) with the goal of achieving light emission, transparency, and good mechanical properties. A series of near-infrared (NIR) luminescent cellulose nanopapers were prepared via 2D Ln-MOF-grafted (2,2,6,6-tetramethylpiperidin-1-yl)oxyl-oxidized cellulose nanofibrils (tCNFs; Ln = Nd, Yb, or Er). In addition to efficient NIR luminescence, these Ln nanopapers exhibited good flexibility, transparency (>90%), and mechanical properties (>28 MPa). Notably, the haze of these nanopapers was increased by 93-95% from 26% due to compositing with 2D Ln-MOFs, which prevented dense packing among the cellulose and formed air cavities in the nanopaper, inducing internal light scattering and improving optical haze. Moreover, these flexible Ln nanopapers exhibited efficient NIR luminescence, which, together with optical haze and transparency, offered an opportunity for utilization in paper-based anticounterfeiting, NIR-light-emitting diodes, or light softening devices.

Efficient near-infrared luminescence from bis-cyclometalated iridium(iii) complexes with rigid quinoline-derived ancillary ligands

Five new near-infrared (NIR) phosphorescent bis-cyclometalated iridium(iii) complexes, partnering highly conjugated cyclometalating ligands with quinoline-derived ancillary ligands, have been developed. These complexes have peak NIR luminescence wavelengths from 711 to 729 nm, with photoluminescence quantum yields ranging from 0.042 to 0.36.

Covalently-bonded grafting of [Ln3(Benzimidazole)4]-arrayed (Ln = Tb, Nd, Yb or Er) complex monomers into PNBE (poly(norbornene)) with highly luminous color-purity green-light or efficient NIR luminescence

Within series of Ln3-grafted polymers Poly({[Ln3(L)4(NO3)6]·(NO3)·(H3O)2}-co-NBE) (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; Ln = Nd, 4; Ln = Yb, 5; Ln = Er, 6 or Ln = Gd, 7) obtained from ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with each of allyl-functionalized complex monomers {[Ln3(L)4(NO3)6]·(NO3)·(H3O)2} (HL = 4-allyl-2-(1H-benzo[d]imidazol-2-yl)-6-methoxyphenol), PNBE-assisted effective energy transfer renders Poly(3-co-NBE) Tb3+-centered highly luminous color-purity green-light with an attractive quantum yield of 87% and efficient near-infrared (NIR) luminescence (ΦNdL = 0.61%; ΦYbL = 1.47% and ΦErL = 0.03%) for Nd3+-, Yb3+- or Er3+-grafted polymers.

Downshifting by energy transfer in Eu3+/Yb3+ codoped Ba4La6(SiO4)6O glass ceramics

We report on an efficient near-infrared downshifting in Eu3+/Yb3+ codoped glass ceramics containing Ba4La6(SiO4)6O crystals. The structural and luminescence properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), static and dynamic photoemission and excitation spectroscopy. After crystallization, the doping ions are found to be selectively incorporated into the precipitated oxyapatite crystals on La3+ sites, contributing to the remarkably enhanced visible emission of Eu3+ under 394nm excitation. The Eu3+/Yb3+ codoped glass ceramics additionally exhibits efficient near-infrared luminescence of Yb3+ around 1000nm upon photon excitation of Eu3+ within the 300–550nm range. The reduced visible emission and decay time of 5D0 state with Yb3+ codoping further confirm the energy transfer from Eu3+ to Yb3+, which is promoted due to the shortened distance between Eu3+ and Yb3+ within crystals. The maximum energy transfer efficiency is evaluated to be 61%. It is revealed that energy transfer process occurs predominantly through the cross relaxation of Eu3+(5D0) + Yb3+(2F7/2) → Eu3+(7F6) + Yb3+(7F5/2).

All-inorganic water-dispersible silicon quantum dots: highly efficient near-infrared luminescence in a wide pH range

We report a novel method to prepare silicon quantum dots (Si-QDs) having excellent stability in water without organic-ligands by simultaneously doping phosphorus and boron. The codoped Si-QDs in water exhibit bright size-tunable luminescence in a biological window. The luminescence of codoped Si-QDs is very stable under continuous photoexcitation in water.

Bismuth-sensitized efficient near-infrared luminescence from ytterbium in zeolites

Yb–Bi co-doped zeolites are prepared by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. We observe two strong near-infrared (NIR) emission bands overlapping in the range 930–1480 nm, corresponding to the electronic transitions of bismuth-related active centres (BiRAC) and Yb3+ ions, respectively. In the obtained products, the excitation wavelength of Yb3+ is extended to the range 420–850 nm, and the lifetime reaches 665 µs. In the zeolite matrix, Bi ions exist as BiRAC and Bi compound agglomerates. The former act as a sensitizer of Yb3+ ions, and the latter act as a blockage to seal the pores of zeolites, which enables Yb3+ ions to show efficient NIR emission even if the zeolites contain a large amount of coordinated water. The excellent optical and structural properties make these NIR-emitting nanoparticles promising in applications as biological probes.

Efficient near-infrared luminescence and energy transfer in Nd-Bi codoped zeolites

ABSTRACTWe prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970∼1450 nm, corresponding to the electronic transitions of Nd3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd3+ in the visible region, and the lifetime of Nd3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes.

Efficient near-infrared luminescence and energy transfer in erbium/bismuth codoped zeolites

We have shown that tunable and highly efficient broadband near-IR (NIR) luminescence can be realized in erbium/bismuth codoped zeolites. The emission covers the ranges of 930-1450nm and 1450-1630nm. The intensity ratio of the two bands can be tuned by adjusting the concentration of erbium and the excitation wavelength. Steady-state and time-resolved photoluminescence (PL), and PL excitation measurements indicate that two kinds of emitters coexist in the pores of zeolites, and that NIR active bismuth simultaneously acts as a sensitizer of erbium. The present results demonstrate an important rational strategy for the design of a tunable NIR-emitting zeolite-based nanosystem.

Polygermyne: Germanium sheet polymers with efficient near-infrared luminescence

ABSTRACTThe structural, optical and electronic properties of the Ge sheet polymer poylgermyne are summarized. Prepared via topotactic transformation of Zintl-phase CaGe2, (GeH)n forms a layered crystal in a tr6 stacking sequence with a distance of 5.65 Å between adjacent layers. The photoluminescence at 1.3 eV is excited nearly resonantly with a Stokes shift of 0.2 eV. Together with band structure calculations this shows that polygermyne has a direct band gap.