Luminescence Wavelength Research Articles

Synthesis and luminescence properties of substituted benzils

Photophysical properties of benzil (1,2-diphenylethane-1,2-dione) and its derivatives in the crystal state have recently attracted much attention. However, the study of substituted benzils has mostly been limited to para-substituted derivatives, which did not induce a significant effect on the emission wavelength compared to pristine benzil. The effects of ortho- and meta-substituents on the photophysical properties in the crystal state have not been investigated so far. Our recently developed organocatalytic pinacol coupling of substituted benzaldehydes allowed us to prepare various ortho-, meta-, and para-substituted benzil derivatives and to investigate their luminescence properties. Ortho- and meta-substituents affected the electronic states of benzils in the crystal state, resulting in differences in their luminescence properties. The luminescence wavelength and type, i.e., phosphorescence or fluorescence, were altered by these substituents. Fast self-recovering phosphorescence-to-phosphorescence mechanochromism by the para-CF3 substituent at room temperature was also discovered.

Introducing Relatively Isolated In/Out‐Gap Bands in Cs2XCl6 (X = Sn, Hf, Zr, Ti) via B‐Site Substitution: A Route to Brighter Luminescence and Tunable Emission Wavelengths (Advanced Optical Materials 21/2023)

Introducing Relatively Isolated In/Out‐Gap Bands in Cs₂XCl₆ (X = Sn, Hf, Zr, Ti) via B‐Site Substitution: A Route to Brighter Luminescence and Tunable Emission Wavelengths (Advanced Optical Materials 21/2023)

Introducing Relatively Isolated In/Out‐Gap Bands in Cs2XCl6 (X = Sn, Hf, Zr, Ti) via B‐Site Substitution: A Route to Brighter Luminescence and Tunable Emission Wavelengths

AbstractBoth theoretical and experimental approaches are utilized to investigate the fluorescence mechanism of B‐site substituted Cs2XCl6 (A2BX6‐type perovskite, X = Sn, Hf, Zr, Ti), aiming to enhance the luminescence and tune the emission wavelengths. Using Te‐monosubstituted Cs2SnCl6 as a model system, thecomputational discovery that the introduction of out‐gap and in‐gap bands by Te can significantly enhance its transition dipole moment is reported. This is further experimentally confirmed, showing a single emission peak resulting from the radiative transition between the out‐gap and in‐gap bands. The broadening of the emission peak is attributed to self‐trapped exciton (STE), while additional absorption/excitation peaks arise from composition segregation. Additionally, the high‐throughput first‐principles calculations indicate that substituting B‐sites of Cs2XCl6 with Se, Te, Po, As, Sb, and Bi may also significantly enhance their light emission with the introduced bands. Thus, fine‐tuning the emission wavelengths by controlling the position of out‐gap and in‐gap bands through cation selection is proposed. Furthermore, tunable white‐light emission is achieved with excellent color stability by adjusting the Te and Bi composition in co‐substituted Cs2SnCl6 material. The findings highlight the potential of utilizing out‐gap and in‐gap bands to tune luminescence in this perovskite family for advanced device applications, including white‐light‐emitting diodes (WLEDs).

Light Enhancement of Green Up-Conversion Emission from Er-Doped Silica Microspheres by Carbon Quantum Dot Coatings.

Combination of high quality cavity such as glass microsphere and emitting nano-particle coating layers can create novel strongly emitting devices. Herein, we demonstrate an erbium-doped silica microsphere coated by dual-emission carbon quantum dots, which have the sizes of 3-5nm, emitting green up-conversion with narrow line-width green light at wavelength of 537nm. The dual-emission carbon quantum dots fabricated by hydrothermal process and have luminescent emission wavelengths in the range of 410-550nm. The carbon quantum dot coated erbium silica microsphere is pumped at wavelength of 976nm through the optical fibre on which microsphere attached on the tip. The dual-emission carbon quantum dot layers attributed to the strong green up-conversion light enhancement similar coated noble metallic thin films, however the light enhancement from dual-emission carbon quantum dot coated erbium silica microsphere depended on the thickness of coating layers. This result is useful for making visible emitting micro-devices and photonic integrated circuits.

Thermodynamic characteristics of sodium ditungstate single crystal

The single crystal of Na2W2O7 has been grown by the low-temperature-gradient Czochralski technique. The thermo- dynamic properties (standard enthalpy of formation, lattice enthalpy and stabilization energy), the knowledge of which is necessary to improve the growth technology, have been measured using reaction calorimetry. It has been shown that in the Na2W2O7– Na2Mo2O7 series, the luminescence wavelength increases from 540 to 650 nm, respectively, along with a change in the lattice enthalpy from −49030 to −54730 kJ mol−1.

Multiband Monochromatic Upconversion Emissions of Lanthanide Codoped Monolayer MoS2 Nanosheets for Lighting Applications

Upconversion materials have attracted much attention because of their broad application prospects in biomedicine and energy. Although various methods have been tried in nanoparticles and nanocrystals, it is still a challenge to realize monochromatic upconversion luminescence (UCL) in traditional lanthanide-doped materials. Two-dimensional transition metal chalcogenides (2D-TMDs) are a class of excellent luminescent semiconductors, offering a promising platform due to their chemical accessibility and physical sensitivity. However, multi-lanthanide doping, typically boosting the upconversion efficiency, has not been accomplished in monolayer TMD nanosheets. In this work, an optimized liquid precursor-assisted technique is designed to synthesize monolayer MoS2 nanosheets embedded with Er/Yb and Er/Ho by surmounting the precipitation of Ln3+-doped precursors, which is confirmed by structural characterization. The monolayer MoS2 can split the 4f configuration remarkably to produce diverse energy levels due to its strong Coulomb binding and spin–orbit coupling, as well as the unique asymmetric crystal field along the [001] direction. Hence, multiband monochromatic UCL from violet to near-infrared ranges was obtained on these codoped MoS2 nanosheets. This work provides an effective way to tune the luminescence performance and wavelength of 2D-TMD nanosheets as well as a strategy for the design of UCL nanomaterials for light applications as nanophotonic devices.

Template Pore Size and A‐Site Cation Management Dictate Luminescence Efficiency, Stability, and Wavelength in Confined Perovskite Nanostructures

AbstractA‐site cation composition is a useful lever in optimizing the photophysical properties and stability of metal halide perovskites (MHPs). Independent of this, straightforward preparative routes to MHP nanostructures that employ a single solid‐state template with modest thermal requirements are also in demand. Here both strategies are employed in the fabrication and evaluation of luminescence properties of mixed formamidinium/cesium (CsxFA1−xPbBr3) and methylammonium/cesium (CsxMA1−xPbBr3) nanostructures formed within confining mesoporous silica of 4 and 7 nm average pore diameters. Use of such small‐pore oxide‐terminated templates produce perovskite nanostructures in the strongly confined regime, with broadly tunable emission from green to sky blue. It is found that the smallest nanostructures that are formamidinium rich exhibit the largest photoluminescence quantum efficiency values, but such values diminish by more than 50% in a 10 day period. In contrast, the same nanostructures formed within a 7 nm porous template retain their efficiency values over the same time window. The likely origins of this size‐dependent behavior are discussed in terms of pore‐size‐dependent capillary forces. Such routes may ultimately lead to improved light‐emitting diode designs composed of controlled quantum‐confined perovskites of greater intrinsic stability than other emitters such as ligand‐based colloidal nanocrystals.

Photoluminescence from Cu / Mn: ZnSe quantum dots and their phase transformation in silicate glass

To realize the polychromatic and tunable luminescence of ZnSe quantum dots (QDs) in glass, Cu and Mn co-doped ZnSe QDs (Cu/Mn: ZnSe QDs) glass were prepared by melt quenching and subsequent heat treatment method. For the ZnSe QDs glass without Cu and Mn dopants, there is only intrinsic luminescence from ZnSe QDs observed. For Cu/Mn: ZnSe QDs glass, the band edge emission from ZnSe QDs is quenched and the broadband emission from Cu2+/Mn2+ ions is observed, which is resulted by the effective energy transfer from ZnSe QDs to Cu2+/Mn2+ ions. With the increase of heating temperature, the emission spectra of Cu/Mn: ZnSe QDs glass change from green to orange light, which is characteristic luminescence wavelengths of Cu2+ and Mn2+ ions, respectively. For the ZnSe QDs glass without Cu2+ and Mn2+ dopants, ZnSe QDs undergo a phase transformation from the cubic to the hexagonal structure at higher heating temperature (≥610 °C) than those of Cu/Mn: ZnSe QDs glass at 600 °C and Cu-doped ZnSe QDs glass at 580 °C, in addition, For Cu/Mn: ZnSe QDs glass, the phase transformation temperature drops to 600 °C. For Cu-doped ZnSe QDs glass, the phase transformation temperature is further reduced to 580 °C. However, for Mn-doped ZnSe QDs glass, there is no phase transformation. It indicated that Cu2+ promotes the phase transformation of ZnSe QDs.

Mechanically Responsive Circularly Polarized Luminescence from Cellulose-Nanocrystal-Based Shape-Memory Polymers.

Stimulus-responsive materials that display circularly polarized luminescence (CPL) have attracted great attention for application in chiral sensors and smart displays. However, due to difficulties in the regulation of chiral structures, fine control of CPL remains a challenge. Here, it is demonstrated that cellulose nanocrystal shape-memory polymers (CNC-SMPs) with luminescent components enable mechanically responsive CPL. The chiral nematic organization of CNCs in the material gives rise to a photonic bandgap. By manipulating the photonic bandgap or luminescence wavelengths of the luminescent CNC-SMPs, precise control of CPL emission with varied wavelengths and high dissymmetry factors (glum ) is achieved. Specifically, CPL emission can be switched reversibly by treating the luminescent CNC-SMPs with hot-pressing and recovery by heating. Pressure-responsive CPL with tunable glum values is ascribed to the pressure-responsive photonic bandgaps. Moreover, colorimetric and CPL-active patterns are created by imprinting desired forms into SMP samples. This study demonstrates a novel way to fabricate smart CPL systems using biomaterials.

Concentration-regulated multi-color fluorescent carbon dots for the detection of rifampicin, morin and Al3+

Carbon dots have many new and interesting phenomena, and the concentration dependent luminescence wavelength is an intriguing one. Herein, nitrogen-sulfur co-doped carbon dots (NSCDs) diluted to different concentrations, the high concentration of G-NSCDs (0.2 mg mL−1) with green fluorescence and the low-concentration of B-NSCDs (0.01 mg mL−1) with blue fluorescence were obtained. Further, it was found that the detection behaviors are different for different concentrations. The “turn-off” fluorescent sensor of G-NSCDs can specifically recognize rifampicin in a linear range of 0.2–20 μM with a detection limit of 56.6 nM employing the mutual effect of photo-induced electron transfer and dynamic quenching. Meanwhile, a “turn-off” B-NSCDs fluorescence sensor was constructed to effectively identify morin based on the internal filtration effect and static quenching, achieving a suitable linearity of 0.2–30 μM and a detection limit of 51.2 nM. Due to the strong chelation of morin and Al3+, a “turn-on” fluorescent probe for sequential detection Al3+ was fabricated based on B-NSCDs-morin system, obtaining a good linearity of 0.1–2.0 μM with a satisfactory detection limit of 45.8 nM. These interesting behaviors indicate that NSCDs are expected to become novel sensing materials for the monitoring of rifampicin, morin and Al3+ in organisms, which is beneficial for our health.

Interfacial self-assembly of Cd2+-tetraphenylethylene coordination polymers and their photophysical properties in Langmuir-Blodgett films

Molecular arrangement and orientation of tetraphenylethylene (TPE) unit in the highly ordered thin films and aggregates can effectively limit its conformation that results in strong effect on the excited energy transfer process and luminescent behaviors under irradiation. We report here an interfacial self-assembly of metal-TPE coordination polymer (CP) ultrathin films and their aggregate-induced emission (AIE) behaviors. After connected with pyridyl or benzimidazole substituents, the tetradentate TPEs as synthesized are used as the multidentate linkers to coordinate with the Cd2+ ions to produce aggregates in the solutions, and to form well-defined two- and three-dimensional organized Cd-TPE CP multilayers at the air-water interfaces by the Langmuir-Blodgett (LB) method. It is revealed that, in addition to the aggregation-induced emission, the following external factors have also large effects on the luminescence of TPEs, including the coordination bonding in the CPs, in plane and interlayer molecular interaction in the LB films; both of them can restrict the intramolecular motion or rotation of TPE unit. Because of these external effects, the emission lifetime of TPEs reaches to approximately 5–10 times longer in some Cd-TPE CP LB films than that in the solutions. Further, the luminescent emission wavelengths and colors of LB films can be tuned to some extent by the in-plane and interlayer molecular interaction. Finally, it is demonstrated that the luminescent emissions and colors of the Cd-TPPE CP LB films is selectively sensing to methanol and formic acid in the gas phase with good reversibility and reproductivity.

Highly Efficient Wavelength-Tunable Circularly Polarized Luminescence Film Constructed by Responsive Chiral Aggregation-induced Emission Luminophore.

Key Lab of Environment-friendly Chemistry and Circularly polarized luminescent (CPL) materials with multitudinous inherent advantages shows extensive application. In this work, we prepare a kind of highly efficient wavelength-tunable CPL free-standing films by responsive chiral aggregation-induced emission mesogen. Firstly, the pyridine-functionalized tetraphenylethene monomer (MPy) is designed and synthesized. Then, the different ration of the monomer MPy mixed with the liquid crystal (LC) reactive monomer (LC242) to fabricate a free-standing film by photopolymerization. The obtained film presents efficient CPL with a constant luminescence asymmetry factor (glum ) of +0.75, as well as sensitive wavelength tunability. Finally, this wavelength-tunable CPL film with both fluorescence and CPL modes is successfully applied in anti-counterfeiting and information encryption. This work provides a simple way to construct CPL apparatus with adjustable luminescence wavelength and high glum .

Remarkable luminescence regulation covering full visible wavelength range of zero-dimensional indium-based metal halides

Recently, there has been a lot of research into the use of zero-dimensional (0D) metal halides as new luminous materials. However, the wide-range tunability of luminescence properties by structural engineering need to be explored. Here, we report the vacuum solid-state reaction synthesis of a series of indium-based A3InX6 (A = K, Rb, or Cs; X = Cl, Br, or their mixture) 0D metal halide single crystals (SCs). Alkali metal substitution at A site leads to similar luminescence properties but very different stability, among which Rb3InCl6 was the most air stable. Halogen alloying at the X site of Rb3InX6 can produce a luminescence wavelength modulation from 436 to 505 nm. The luminescence wavelength was further extended by Sb3+ doping to the 509–622 nm region. Finally, due to the high luminescence tunability covering the full visible wavelength range, we achieved pure white light-emitting diodes utilizing a combination of Rb3InBr2Cl4 and Rb3InBr2Cl4:Sb3+ SCs. This work provides a strategy with simultaneous substitution, alloying, and doping to modulate the luminescence properties of 0D lead-free metal halides for a variety of applications.

Effective electroluminescence performance improvement of bis-tridentate iridium complexes by triptycene group modification

To inhibit concentration quenching, three new bis-tridentate iridium complexes modified with triptycene groups were successfully synthesized. The rigid sterically demanding triptycene endows these new complexes with high photoluminescence quantum yields (PLQYs) and low concentration quenching. In air, their PLQYs exceed 0.68 in poly(methyl methacrylate) (PMMA) films and 0.17 in neat powder form, which are significantly higher than that of the reference complex (0.57 and 0.03, respectively). At the same time, the thermal stability of the complex Ir1 is improved and the luminescence wavelength of the complex Ir1 is less affected by the modification of triptycene group. The doped OLED device based on complex Ir1 exhibits excellent electroluminescent efficiencies of 80.1 cd A−1 and 24.0%, which are improved by more than 50% compared with that of reference device. More significantly, the maximum efficiencies of its non-doped device are 17.6 cd A−1, 7.4%, which are improved by more than 300% compared with that of reference device. These results indicate that the triptycene group is very effective functional group to inhibit the concentration quenching of bis-tridentate iridium complexes.

Controllability of luminescence wavelength from GeSn wires fabricated by laser-induced local liquid phase crystallization on quartz substrates

We examined the effects of the laser scan speed and power on the Sn fraction and crystallinity of GeSn wires of 1 μm width and 1 mm length fabricated by laser-induced local liquid phase crystallization on quartz substrates. The Sn fraction increased from 1% to 3.5% with an increasing scan speed from 5 to 100 μm s−1, corresponding to a luminescence wavelength of 1770–2070 nm. This result can be interpreted as the scan speed dependence of the non-equilibrium degree during crystal growth. The increase in the laser power reduced the Sn fraction and caused a blue shift in the luminescence wavelength. We discuss these phenomena based on the growth kinetics of zone melting.

Excitation-wavelength-dependent photochromic Bi3+/Ln3+(Eu3+, Er3+)-codoped phosphors for anticounterfeiting applications

Fluorescent powders exhibiting excitation dependence and luminescent discoloration are profoundly relevant for concealing information and enhancing optical antiforgery protection. In this study, Bi3+/Ln3+ (Eu3+, Er3+)-doped phosphors exhibiting multicolor luminescence and excitation wavelength dependence were synthesized. The Bi3+/Eu3+-codoped phosphors emitted blue, pink, lavender, and red lights under excitation from conventional ultraviolet (UV) sources. In addition to emitting blue light, the Bi3+/Er3+-codoped phosphors also transmitted upconversion-emission light from green to yellow under 980-nm laser excitation. Additionally, the luminous color of the Ca3Y2Ge3O12:0.01Bi3+, 0.2Er3+ phosphor changed from yellow to orange as the temperature increased. Combining the above luminous-color-change phenomena, the word-hiding experiment exhibited excellent realistic information hiding, with complex color transformation in the stamen and petal parts of the flower pattern. Furthermore, rapid multimodal and complex discoloration was achieved using easy-to-obtain light sources, confirming the potential of Bi3+/Ln3+ phosphors for anticounterfeiting applications.

New Observations on Concentration‐Regulated Carbon Dots

Carbon dots have many new and interesting phenomena and the concentration‐dependent luminescence wavelength is an intriguing one. Luminescent carbon dots have recently gained interest due to their new and interesting phenomena such as its concentration‐dependent peak emission. While there have been reports and discussions on this phenomenon, the mechanism continues to be poorly understood. Herein, new observations on nitrogen–sulfur codoping carbon dots (NSCDs) diluted at different concentrations show that the high concentration of G‐NSCDs (0.2 mg mL−1) emits green fluorescence while the low concentration of B‐NSCDs (0.01 mg mL−1) emits blue fluorescence. It is found that the carbon dot size changes with the particle concentration: the high concentration of G‐NSCDs is about 37 nm in size while the low concentration of B‐NSCDs is only about 1.8 nm in size. Therefore, it is clearly demonstrated that the emission wavelength is related to the particle size. These interesting behaviors open a door for the exploration of new materials with novel potential.

Tuning the luminescence of thin nanocrystalline CsPbBr-=SUB=-3-=/SUB=- perovskite films during the in situ anion exchange reaction

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3-x)Ix and CsPbBr(3-y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode. Keywords: inorganic perovskite nanocrystals, anion exchange, thin films, photoluminescence.

Recent advances in the design of afterglow materials: mechanisms, structural regulation strategies and applications.

Afterglow materials are attracting widespread attention owing to their distinctive and long-lived optical emission properties which create exciting opportunities in various fields. Recent research has led to the discovery of many new afterglow materials featuring high photoluminescence quantum yields (PLQY) and lifetimes of up to several hours under ambient conditions. Afterglow materials are typically categorized according to their luminescence mechanism, such as long-persistent luminescence (LPL), room temperature phosphorescence (RTP), or thermally activated delayed fluorescence (TADF). Through rational design and novel synthetic strategies to modulate spin-orbit coupling (SOC) and populate triplet exciton states (T1), luminophores with long lifetimes and bright afterglow characteristics can be realized. Initial research towards afterglow materials focused mainly on pure inorganic materials, many of which possessed inherent disadvantages such as metal toxicity or low energy emissions. In recent years, organic-inorganic hybrid afterglow materials (OIHAMs) have been developed with high PLQY and long lifetimes. These hybrid materials exploit the tunable structure and easy processing of organic molecules, as well as enhanced SOC and intersystem crossing (ISC) processes involving heavy atom dopants, to achieve excellent afterglow performance. In this review, we begin by briefly discussing the structure and composition of inorganic and organic-inorganic hybrid afterglow materials, including strategies for regulating their lifetime, PLQY and luminescence wavelength. The specific advantages of organic-inorganic hybrid afterglow materials, including low manufacturing costs, diverse molecular/electronic structures, tunable structures and optical properties, and compatibility with a variety of substrates, are emphasized. Subsequently, we discuss in detail the fundamental mechanisms used by afterglow materials, their classification, design principles, and end applications (including sensing, anticounterfeiting, and photoelectric devices, among others). Finally, existing challenges and promising future directions are discussed, laying a platform for the design of afterglow materials for specific applications.

Изменение люминесценции тонких нанокристаллических пленок перовскита CsPbBr-=SUB=-3-=/SUB=- в ходе реакции анионного обмена in situ

Inorganic perovskite CsPbX3 nanocrystals (PNCs), where X is a halide anion, are currently promising materials for a wide range of optoelectronic devices. One of the key tasks to be solved before they are used in practice is to obtain stable thin PNC films whose luminescence wavelength could be finely tuned. The chemical composition of CsPbX3 PNCs is the main parameter determining their band gap width and, hence, the position of their photoluminescence maximum. Variation of the PNC composition in the course of their synthesis or postsynthetic treatment in solution makes it possible to obtain CsPbBr(3–x)Ix and CsPbBr(3–y)Cly materials emitting in the entire visible spectral range. In addition, these PNCs are more structurally stable than CsPbCl3 and CsPbI3 ones. However, most exchange reactions in solution reported in published studies are spontaneous and poorly controllable. In this study, the anion exchange reaction is proposed to be carried out directly on the formed thin film of CsPbBr3 incorporated in the matrix of a copolymer of methyl and lauryl methacrylates. The exchange reactions with octadecylammonium iodide and PbI2 leading to a shift of the photoluminescence maxima to longer wavelengths by 130 and 137 nm within 15 and 6 min, respectively. The study also shows the possibility of carrying out an ion exchange reaction on a substrate mimicking the real structure of a light-emitting diode.