Temperature-dependent Emission Research Articles

A novel borate phosphor Lu5Ba6B9O27:Ce3+ codoped with Sr2+/Tb3+ for NUV-white light emitting diode application.

At present, there are still challenges in developing highly efficient and thermally stable phosphors for ultraviolet/near ultraviolet-white light emitting diodes (UV/NUV-WLEDs). Herein, we use traditional high-temperature solid-state reactions to prepare blue-emitting phosphors Lu5-xBa6B9O27:xCe3+ (0.1% ≤ x ≤ 3.0%) and Lu4.975Ba6-ySryB9O27:0.5%Ce3+ (0% ≤ y ≤ 20%), and green-emitting phosphors Lu4.975-zBa6B9O27:0.5%Ce3+,zTb3+ (0% ≤ z ≤ 16%), abbreviated as LBB:xCe3+, LBB:0.5%Ce3+,ySr2+ and LBB:0.5%Ce3+,zTb3+, respectively. Upon 340 nm excitation, LBB:Ce3+ exhibits an asymmetric blue emission ranging from 360 nm to 480 nm. Furthermore, the emission intensity of LBB:0.5%Ce3+ increased 4.8-fold without a spectral shift through the partial substitution of Sr2+ for Ba2+. Through constructing the Ce3+ → Tb3+ energy transfer in the LBB structure, the temperature-dependent integral emission intensity at 483 K improved from only 25% to 68% of the intensity at 303 K due to the existence of fast energy transfer from Ce3+ to Tb3+. The related results indicate that LBB:xCe3+, LBB:0.5%Ce3+,ySr2+ and LBB:0.5%Ce3+,zTb3+ phosphors can be used for UV/NUV-WLEDs.

Luminescence and spectroscopic studies on Dy3+-Eu3+ doped SiO2-B2O3-ZnO-La2O3-BaO glass for WLED

A series of SiO2-B2O3-ZnO-La2O3-BaO (SBZLBa) glasses doped with Dy3+ and Eu3+ were synthesized using the melt-quenching technique. Their optical characteristics and potential applications in W-LED devices were investigated. The structural effects resulting from doping the glass with Dy3+ and Eu3+ ions were elucidated through infrared spectroscopy and an examination of the physical properties. The variations in emission intensity within the fluorescence spectrum validated the sensitizing effect of Dy3+ on Eu3+ within the glass matrix. By manipulating the transitions of both Dy3+ and Eu3+, the excitation wavelength was altered, enabling the realization of cool white, neutral white, and warm white luminescence, thus accommodating the diverse requirements for white light emission in lighting applications. After incorporating 1.0 mol% of Dy2O3 and 0.8 mol% of Eu2O3, respectively, the glass exhibited CIE coordinates of (0.3332, 0.3535), positioning it within the white light spectrum and in close proximity to the ideal white light coordinates of (0.33, 0.33). The SBZLBa-Dy2O3–0.8Eu2O3 glass exhibited a quantum yield of 5.98 %. It has been demonstrated through acid and alkali resistance tests that this glass possesses excellent chemical stability. Additionally, temperature-dependent emission spectra have revealed that the luminous intensity of the glass maintains over 85 % of its room temperature value at 185 °C, with Eα determined to be 0.2387 eV.

Approaching the emissivity of CMAS at high temperatures by convenient thermocouple-based infrared thermography

It remains a grand challenge to probe the emissivity of calcium-magnesium-alumina-silicates (CMAS) at high temperatures. Herein, an innovative thermocouple-based infrared thermography (TBIT) method that combines a double hot thermocouple system and infrared (IR) camera is proposed to enable convenient measurement for CMAS emissivity at temperature >800 °C. To improve the measurement accuracy, a heat transfer model accounting for the possible uncertainty in temperature measurement is also developed to correct the real sample temperature on the hot thermocouple. On this basis, the feasibility of the TBIT method is verified by using the platinum-rhodium alloy as the benchmark. As a proof-of-principle demonstration, four different sets of CMAS samples, i.e., blast furnace (BF) slag are considered with their temperature-dependent emissivities characterized experimentally. It is found that the BF-like CMAS features an emissivity of 0.5–0.9 at 800–1500 °C. This research provides a fast, accurate and low-cost experiment effort to probe CMAS emissivity at high temperatures, which enriches the thermophysical properties of the CMAS materials.

Crystal-Rigidifying Strategy in Hybrid Manganese Halide to Achieve Narrow Green Emission and High Structural Stability.

Although organic-inorganic hybrid Mn2+ halides have advanced significantly, achieving high stability and narrow-band emission remains enormously challenging owing to the weak ionic nature and soft crystal lattice of the halide structure. To address these issues, we proposed a cationic engineering strategy of long-range cation π···π stacking and C-H···π interactions to simultaneously improve the crystal structural stability and rigidity. Herein, two organic zero-dimensional (0D) manganese halide hybrids of (BACQ)2MnX4 [BACQ = 4-(butylamino)-7-chloroquinolin-1-ium; X = Cl and Br] were synthesized. (BACQ)2MnX4 display strong green-light emissions with the narrowest full width at half-maximum (fwhm) of 39 nm, which is significantly smaller than those of commercial green phosphor β-SiAlON:Eu2+ and most of reported manganese halides. Detailed Hirshfeld surface analyses demonstrate the rigid environment around the [MnX4]2- units originating from the interactions between [BACQ]+. The rigid crystal structure weakens the electron-phonon coupling and renders narrow fwhm of these manganese halides, which is further confirmed by temperature-dependent emission spectra. Remarkably, (BACQ)2MnX4 realizes outstanding structural and luminescence stabilities in various extreme environments. Benefiting from the excellent performance, these Mn2+ halides are used to assemble light-emitting diodes with a wide color gamut of 105% of the National Television System Committee 1931 standard, showcasing the advanced applications in liquid-crystal-display backlighting.

First Principles Study of Europium doped Gallium Nitride in Wurzite Structure

In the present work, we have successfully deposited Sb antimony doped tin dioxide (SnO2) thin films with Several advantages over well known LCD's including increased brightness and viewing angle. We are currently investigating Eu doped GaN as a potential red phosphor for TEFL display applications. Eu doped GaN films were grown by solid source molecular beam epitaxy on Si (111) substates. The material was optically characterized through temperature dependent emission spectroscopy using a He-Cd laser at 325 nm for above band gap excitation. A strong red emission was obtained at 622 nm, which corresponds to an Eu3+ inner 4f-shell transition from the 5D 0 to 7F2 state. Therefore, the observed thermal quenching of red Eu emission is assigned to a strongly temperature dependent pumping process.

Impact of the spatial structure of alkyl chains on properties of thiophene-substituted diketopyrrolopyrroles: Part II – Spectroscopic study

The study concerns the impact of a difference in geometry of the side alkyl chains of oligothiophene derivatives of diketopyrrolopyrrole (DPP) on their spectroscopic properties and aggregation in solutions, in Langmuir layers, and thin films. Using a combination of theoretical and experimental approaches, this study aims to explain the aggregating behaviour of thiophene-substituted DPP derivatives. Various methods were used to characterise the dyes, including absorption spectroscopy also with polarized light, fluorescence spectroscopy, Langmuir techniques, and time-dependent density functional theory (TD-DFT) calculations. The presented results emphasise a significant impact of side alkyl chains on DPP's molecular behaviour, notably evident in thin-layer structures. Interestingly, the deconvolution of the absorption spectra revealed three bands in the red region. Insightful analysis of temperature-dependent absorption, excitation, and emission fluorescence spectra indicates the co-existence of monomer, dimer, and a higher aggregate forms, most likely a tetrameric structures. Moreover, such a complexity of molecular organisation of dyes appears already in the solution. Differences in spectral properties of the dyes studied are robustly visible in changes in the spectra of the air–water interface, where the dye with the branched side group changes the mutual orientation in dimeric structures, leading to the formation of H-type aggregates, which was observed as an almost 20-nm spectral blue shift during Langmuir layer compression. The results presented highlight the need for care in interpretation of the intensity ratio of DPP spectra and spectral shift as the sole determinants of the aggregation state.

Double perovskite quantum dots Cs2AgInCl6: Tb3+/Sm3+/Bi3+ for dual-mode fluorescence temperature sensing

In this research, double perovskite quantum dots Cs2AgInCl6: Tb3+/Sm3+/Bi3+ are synthesized employing a high-temperature thermal injection method. The temperature-dependent emission spectra and the fluorescence decay curves of samples show the quantum dots can be applied to dual-mode temperature sensing employing fluorescence intensity ratio technique (between 656 nm (Sm3+) and 549 nm (Tb3+)) and fluorescence lifetime thermometry (549 nm (Tb3+)), achieving maximal relative sensitivities of 3.24%/K (351 K) and 0.68%/K (373 K), respectively. This study offers valuable insights into the temperature sensing capabilities of these quantum dots, which shows that these quantum dots are promising high-sensitivity dual-mode temperature sensing materials.

Unveiling highly sensitive Dy3+ doped BaMgAl10O17 phosphor’s thermoluminescence trap features and temperature dependent luminescence for solid state lighting applications

This article explores the structural, morphological, thermoluminescence, and temperature-dependent emission properties of novel Dy3+ doped BaMgAl10O17(BAM-Dy) phosphors. Structural studies reveal that the phosphor has a similar structure to β-alumina. Rod-shaped interlinked surface morphology is a notable characteristic of the BAM-Dy samples. Incorporation of Dy3+ ions lead to the formation of distinct emission peaks (485 nm, 577 nm, and 635 nm) in the PL emission spectra. The effect of dopant concentration on the light output is crucial, and the highest PL intensity is observed for 1.5 mol% of Dy3+ concentration. The potential use of BAM-Dy phosphors for Gamma radiation detection and measurement is tested through thermoluminescence studies, which reveal high sensitivity, low threshold dose values, and exceptional response to low gamma doses, making them suitable for dosimetry applications. The investigation of trap parameters provides useful information about the number of traps, trapping mechanism, and trap energies, which is essential for in-depth study of synthesized phosphors for γ dosimetry application. The study of the effect of temperature on the luminescence behaviour is crucial for the application of phosphors in the light-emitting field. The BAM-Dy samples exhibit excellent thermal stability even at 210 °C, making them suitable for use in the field of White LEDs.

Synthesis and optical properties of highly efficient Na7Mg13La(PO4)12:Eu3+ powders with excellent thermal stability

In the pursuit of efficient red-emitting phosphors, a series of red-emitting Na7Mg13La(PO4)12:Eu3+ phosphors was prepared using a high-temperature solid-state synthesis method. The phase purity was monitored using powder X-ray diffraction (XRD). The morphological features of the synthesized samples were evaluated by taking scanning electron microscopy (SEM) images. The optical properties of the synthesized polycrystalline samples were investigated by recording room-temperature and temperature-dependent (77–500 K interval) excitation and emission spectra, and photoluminescence (PL) decay curves. The calculated TQ1/2 values were above 420 K, regardless of the Eu3+ concentration, indicating the high thermal stability of the phosphors. The optimal Eu3+ concentration was 100 %, which indicated the absence of concentration quenching in the given host. Furthermore, the quantum efficiency of fully Eu3+-substituted compound reached 100 %, which is an excellent feature for practical phosphor applications.

LaBaMg(Ti0.5W0.5)O6:Mn4+ for plant growth lighting: Luminescence properties and synthesis

With the need of food safety and high yield, new luminescent materials with promoting plant photosynthesis have attracted more and more attention. In this research, we synthesize the far-red-emitting LaBaMg(Ti0.5W0.5)O6:Mn4+ phosphor in air. We investigate the crystal structure and phase, particle morphology and size, and the luminescence properties. The samples show a broad excitation spectrum under monitored 704 nm due to the Mn4+ - O2− charge transfer (CT) and the transitions 4A2g → 4T1g, 2T2g, and 4T2g of Mn4+ in the range of 300 – 600 nm. The far-red emission of sample is observed with the emission spectrum (650 – 790 nm) is attributed to the Eg → 4A2g transitions. The chromaticity coordinates are (0.7329, 0.2671). The crystal field strength (Dq), the Racah parameters (B and C), and Dq/B values are ∼ 1972 cm−1, 596 cm−1, 3219 cm−1, and 3.31, respectively. 0.2 mol% is the optimal Mn4+ concentration. Emission spectra under excitation wavelength from 320 nm to 560 nm and time-resolved emission spectra confirm the only luminous center (Mn4+) in LaBaMg(Ti0.5W0.5)O6:Mn4+. Lifetime reduces with added Mn4+ concentration. The temperature-dependence emission spectra confirm that sample has a good thermo-stability. The thermal quenching phenomenon and luminous mechanism are analyzed. The luminescence properties of sample infer its application prospect in plant growth light-emitting diode (LED).

Observation of heat pumping effect by radiative shuttling

Heat shuttling phenomenon is characterized by the presence of a non-zero heat flow between two bodies without net thermal bias on average. It was initially predicted in the context of nonlinear heat conduction within atomic lattices coupled to two time-oscillating thermostats. Recent theoretical works revealed an analog of this effect for heat exchanges mediated by thermal photons between two solids having a temperature dependent emissivity. In this paper, we present the experimental proof of this effect using systems made with composite materials based on phase change materials. By periodically modulating the temperature of one of two solids we report that the system akin to heat pumping with a controllable heat flow direction. Additionally, we demonstrate the effectiveness of a simultaneous modulation of two temperatures to control both the strength and direction of heat shuttling by exploiting the phase delay between these temperatures. These results show that this effect is promising for an active thermal management of solid-state technology, to cool down solids, to insulate them from their background or to amplify heat exchanges.

The autoxidation of polyether-polyurethane open cell soft foam: An analytical aging method to reproducibly determine VOC emissions caused by thermo-oxidative degradation

We present a new method for investigating the oxidation and emission behavior of air-permeable materials. Employing this method, a differentiated statement can be made about the extent to which critical volatile organic compounds (VOCs) such as formaldehyde, acetaldehyde, and acrolein are contained in the material as impurities or formed by thermo-oxidative degradation of the polymer matrix in the use phase. The parameters affecting methods of VOC analysis are reviewed and considered for the developed method. The molecular mechanisms of VOC formation are discussed. Toxicological implications of the reaction kinetics are put into context with international guidelines and threshold levels. This new method enables manufacturers of cellular materials not only to determine the oxidative stability of their products but also to optimize them specifically for higher durability. Environmental ImplicationCellular materials are ubiquitous in the technosphere. They play a crucial role in various microenvironments such as automotive interiors, building insulation, and cushioning. These materials are susceptible to oxidative breakdown, leading to the release of formaldehyde, acetaldehyde, and acrolein. The ecotoxicological profiles of these compounds necessitate monitoring and regulation. The absence of reproducible and reliable analytical methods restricts research and development aimed at risk assessment and mitigation. This work significantly enhances the toolbox for optimizing the oxidative stability of any open-cell cellular material and evaluating these materials in terms of their temperature-dependent oxidation and emission behavior.

Confinement of Sustainable Carbon Dots Results in Long Afterglow Emitters and Photocatalyst for Radical Photopolymerization.

Sustainable carbon dots based on cellulose, particularly carboxymethyl cellulose carbon dots (CMCCDs), were confined in an inorganic network resulting in CMCCDs@SiO2. This resulted in a material exhibiting long afterglow covering a time frame of several seconds also under air. Temperature-dependent emission spectra gave information on thermally activated delayed fluorescence (TADF) and room temperature phosphorescence (RTP) while photocurrent experiments provided a deeper understanding of charge availability in the dark period, and therefore, its availability on the photocatalyst surface. The photo-ATRP initiator, ethyl α-bromophenylacetate (EBPA), quenched the emission from the millisecond to the nanosecond time frame indicating participation of the triplet state in photoinduced electron transfer (PET). Both free radical and controlled radical polymerization based on photo-ATRP protocol worked successfully. Metal-free photo-ATRP resulted in chain extendable macroinitiators based on a reductive mechanism with either MMA or in combination with styrene. Addition of 9 ppm Cu2+ resulted in Mw/Mn of 1.4 while an increase to 72 ppm improved uniformity of the polymers; that is Mw/Mn=1.03. Complementary experiments with kerria laca carbon dots confined materials, namely KCDs@SiO2, provided similar results. Deposition of Cu2+ (9 ppm) on the photocatalyst surface explains better uniformity of the polymers formed in the ATRP protocol.

Temperature-dependent excitonic emission characteristics of highly crystallized carbon nitride nanosheets

Highly-crystallized carbon nitride (HCCN) nanosheets exhibit significant potential for advancements in the field of photoelectric conversion. However, to fully exploit their potential, a thorough understanding of the fundamental excitonic photophysical processes is crucial. Here, the temperature-dependent excitonic photoluminescence (PL) of HCCN nanosheets and amorphous polymeric carbon nitride (PCN) is investigated using steady-state and time-resolved PL spectroscopy. The exciton binding energy of HCCN is determined to be 109.26 meV, lower than that of PCN (207.39 meV), which is attributed to the ordered stacking structure of HCCN with a weaker Coulomb interaction between electrons and holes. As the temperature increases, a noticeable reduction in PL lifetime is observed on both the HCCN and PCN, which is ascribed to the thermal activation of carrier trapping by the enhanced electron–phonon coupling effect. The thermal activation energy of HCCN is determined to be 102.9 meV, close to the value of PCN, due to their same band structures. Through wavelength-dependent PL dynamics analysis, we have identified the PL emission of HCCN as deriving from the transitions: σ*–LP, π*–π, and π*–LP, where the π*–LP transition dominants the emission because of the high excited state density of the LP state. These results demonstrate the impact of high-crystallinity on the excitonic emission of HCCN materials, thereby expanding their potential applications in the field of photoelectric conversion.

Ultrastable Copper Iodide Hybrid with Intrinsic Greenish White-Light Emission by Incorporating an Anionic Inorganic Functional Unit into an Extended Structure.

Incorporating a functional unit into the multidimensional coordination polymer skeleton is an efficient way to improve the stability of materials and expand their application. In this paper, anionic copper iodide inorganic functional modules are incorporated into one-dimensional extended chains by using a unique bidentate cationic organic ligand. Benefiting from the ionic extended structure, the resulting hybrid possesses a remarkable stability with a decomposition temperature as high as 300 °C. Meanwhile, the hybrid material exhibits intrinsic greenish white-light emission with a high photoluminescent quantum yield of 70%. The emission was investigated by temperature-dependent emission spectra, which proved to be the result of the synergistic effect of two energy states. The novel synthetic strategy provides an efficient route for the development of functional organic metal halides.

Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands.

The reaction of two equivalents of N,N'-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (H2bppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda)2. Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (ΦPL = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature. TADF emission is strongly quenched by 3O2 and shows highly temperature-sensitive emission lifetimes of hundreds of microseconds. The lifetime of the lowest energy singlet excited state, S1, was established by transient absorption spectroscopy and shows rapid deactivation (τ = 142 ps) by prompt fluorescence and intersystem crossing to the triplet state, T1. Time-dependent density functional theory (TD-DFT) calculations predict moderate ligand-to-metal charge transfer (LMCT) contributions of 25-30% for the S1 and T1 states. A comparison of Zr(bppda)2 to related zirconium pyridine dipyrrolide complexes, Zr(PDP)2, revealed important electronic structure changes due to the eight-coordinate ligand environment in Zr(bppda)2, which were correlated to differences in the photophysical properties between the two compound classes.

Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Pt-S Bond-Enabled Temperature-Dependent Phosphorescence in S-Heteroaryl Tetradentate Pt(S^C^N^O) Complexes.

This study presents the rare examples of S-heteroaryl tetradentate Pt(S^C^N^O) luminescent complexes (PtSZ and PtSZtBu) containing a Pt-S bond. The presence of the Pt-S bond allows the novel Pt(S^C^N^O) complexes to exhibit temperature-dependent phosphorescent emission behavior. The PtSZtBu exhibits dual-emission phenomena and biexponential transient decay spectra above 250 K, indicating the presence of two minimal excited states in the potential energy surface (PES) of the T1 state. Through complementary experimental and computational studies, we have identified changes in orbital composition between Pt(dxy)-S(px) and Pt(dyz)-S(pz) in excited states with increasing temperature. This results in two energy minima, enabling the excited states to decay selectively and radiatively at different temperatures. Consequently, this leads to remarkable steady-state and transient emission spectra changes. Our work not only provides valuable insights for the development of novel Pt-S bond-based tetradentate Pt(II) complexes but also enhances our understanding of the distinctive properties governed by the Pt-S bond.

Optical and photoluminescence properties of trivalent rare earth ions doped LiMgPO4

Trivalent rare-earth-activated luminescent materials have attracted a lot of attention due to their fascinating optical properties and broad range of applications. In this study, polycrystalline Sm and Eu-doped LiMgPO4 luminescent materials were synthesized using a solid-state reaction technique. The crystalline structures, morphological features, and optical characteristics of the synthesized materials were thoroughly investigated using x-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Field-Emission Scanning Electron Microscopy (FE-SEM) and UV–vis spectroscopy. The Rietveld refinement analysis confirmed the phase purity of synthesized phosphors. In addition, the strain induced owing to the incorporation of trivalent rare-earth ions and crystallite sizes of each synthesized material was estimated using the Williamsons-Hall (W-H) and modified Debye-Sherrer equations. The estimated results of the microstrain were reported to be 0.0010, 0.0023 and 0.0020. Subsequently, as a consequence of distinct peak profile options, the projected average crystallite size by both approaches was distinct. The UV–vis spectroscopy analysis reveals that Sm and Eu doped materials exhibit absorption bands around 402 nm and 396 nm and depicts the declining band gap values. The Photoluminescence (PL) spectra at 402 nm and 395 nm excitation wavelengths exhibited the distinctive emissions of both Sm3+ (4G5/2 → 6H7/2) and Eu3+ (5D0 → 7F2) ions emanating due to the intra-configurational f - f and 4 f − 4 f transitions. Finally, the CIE diagram explicitly demonstrates that the Sm and Eu-modified materials reveal their exceptional color purity. McCamy’s approach was used to determine various parameters of trivalent rare-earth doped materials. The correlated color temperature ( TCCT ) and their coordinates TCCT (ζ, β) was found to be 2287 K, 1900 K, 0.281, 0.632, and 0.302, 0.681 respectively. Temperature-dependent emission spectra exhibit excellent color and thermal stability at high temperatures. The obtained results in this study indicate that the synthesized luminescent materials can potentially be used in white light-emitting diode applications.

Temperature sensing of novel Tb3+/Ho3+/Bi3+ co-doped lead-free double perovskite Cs2AgInCl6 nanocrystals

Up to now, the research field of application of lanthanide ions doped lead-free double perovskite Cs2AgInCl6 nanocrystals (NCs) was relatively limited, even less in temperature sensing. Here, Tb3+/Ho3+/Bi3+ ions were successfully doped into Cs2AgInCl6 NCs by hot-injection. The temperature sensing performance of co-doped NCs by using the fluorescence intensity ratio (FIR) was studied through the temperature-dependent emission spectra. By analyzing the influence of ions' doping concentration on temperature sensing performance, the optimal doping concentration of co-doped Cs2AgInCl6 NCs was determined to be 7 % Tb3+, 20 % Ho3+ and 1 % Bi3+. The highest absolute and relative sensitivities reach 1.48 K−1 and 2.48 %/K, respectively. We provide a new doping scheme of lead-free double perovskite NCs which have good temperature sensing performance. This co-doped NCs have great potential application value in non-contact temperature sensing in nanoscale.