Temperature-dependent Luminescence Research Articles

The influence of Ce3+ codoping on upconversion in nanocrystalline NaYF4:Yb3+,Tm3+

Usually, to obtain multicolor upconversion in lanthanides, materials with different codopants, different size, chemical composition or compositional architecture are required. However, designing a material whose emission color can be tuned in-situ by an external stimulus, such as temperature, excitation pulse duration or photoexcitation density, is of great interest for many applications, but still remains a challenge. The possible solution for this issue can be achieved by intentional codoping the luminescent materials with optically active ions which can disturb or compete with other energy transfer processes, and in consequence lead to changes in relative emission intensity, thus the dominant emission color. Here we synthesized and investigated colloidal luminescent Yb3+ and Tm3+ doped NaYF4 nanoparticles which were codoped with optically active Ce3+ ions, whose relative emission intensity ratios between 1D2→3F4 (at 450 nm), 1G4→3H6 (at 475 nm), 1G4→3F4 (at 650 nm), and 3H4→3H6 (at 800 nm) were significantly dependent from external stimulus – namely temperature and/or excitation pulse length. Our results shows two fold increase in 450/800, 470/800 and 650/800 luminescence intensity bands ratios (LIR) only after incorporation of Ce3+ ions to the material, and even three-fold increase in those LIR after changing the excitation conditions (i.e. pulse width). Moreover, temperature dependent luminescence properties revealed relative sensitivity of 4%/K for the 450/800 and 470/800 bands ratio and almost 5.5%/K for the 650/800 band ratio close to 0 °C. By switching to physiological range of temperatures, the thermal sensitivity decreased to around 2%/K for the 450/800 and 470/800 bands ratio and to over 2.5%/K for 650/800 bands ratio, which should be considered as significant values and suitable for temperature sensing in practical applications. It is worth noting that the thermal sensitivity values can be further enhanced by applying different excitation pulse width. The proposed materials allows to tune its emissions as well as thermal properties by changing the dopant concentration or more importantly also in situ, through excitation scheme modifications.

Synthesis, Structure and Luminescence Characterizations of Pyramid-like Lanthanide-Titanium-Oxo Clusters EuTi9 and TbTi9

Two pyramid-like lanthanide − titanium − oxo clusters formulated as LnTi9(µ2-O)5(µ3-O)7(µ3-OH)2(OiPr)(acac)2(TCA)10(THF) (LnTi9, Ln = Eu / Tb, HTCA = 2-thiophenecarboxylic acid) were prepared through the reaction of Ln(acac)3, 2-thiophenecarboxylic acid (HTCA), Ti(OiPr)4 and THF. The 10-nuclearity-metal-core [LnTi9(µ2-O)5(µ3-O)7(µ3-OH)2]13+ is protected by four kinds of ligands. EuTi9 and TbTi9 exhibit characteristic emissions of Eu3+ / Tb3+ under ultraviolet excitation. The temperature-dependent luminescence results show EuTi9 shows a good linear relationship between the luminescence intensity and temperature range of 80–320 K, while TbTi9 has high temperature-sensitivity in different temperature ranges.

Color-tunable photoluminescence and persistent luminescence in a single LiYGeO4:Tb3+ phosphor

Persistent luminescence (PerL) phosphors have been widely applied in many advanced applications in the field of emergency lighting, safety signage, and ornaments. Recently, the PerL phosphors based on germanates have attracted great attention owing to their excellent PerL performance. However, the design and development of excellent germanates-based PerL materials with full spectral emissions remain challenging due to the lack of color-tunable PerL, especially in the blue and green regions (400–600 nm). Herein, we develop a new type of Tb3+-activated LiYGeO4 PerL phosphor with real-time adjusting the photoluminescence (PL) and PerL color, which can be effectively excited by a 254 UV light. Both blue and green PerL are realized simultaneously in a single phosphor. When LiYGeO4:Tb3+ doped with lower concentrations of Tb3+ ions, phosphors emit blue PL and PerL. With increasing Tb3+ concentration, the PL and PerL colors of LiYGeO4:Tb3+ PerL phosphor are gradually regulated from blue to green. Besides, LiYGeO4:Tb3+ exhibits temperature-dependent luminescence property, whose PL and PerL colors can also be successively widely tuned by various temperature. This stable and tunable color in real-time PL and PerL property promote the as-designed LiYGeO4:Tb3+ phosphor to have potential applications in advanced anti-counterfeiting and display devices.

One-step synthesis of YF3:Nd rod-like particles for contactless luminescent thermometers

Nd-doped YF3 rod-like particles have been obtained by one-step and fast synthesis using the microwave hydrothermal method. Before the investigation of the particles as luminescent thermometers, the structural and morphological properties were investigated by XRD, XPS, and SEM techniques. The results indicate that the method ensures the reproducibility of the crystalline phase and the rod-like shape of YF3 particles. The optical absorption reveals typical neodymium transitions that occur in the first biological window, important to applications as sensors in bio-tissues. The optical sensing performance was analyzed using the temperature-dependent luminescence intensity ratio (LIR) from two Stark sublevels of 4F3/2 level (R1 and R2). The maximum value achieved for the relative sensibility (Sr) was 0.22%K−1 at 303K with repeatability of 99.57%, demonstrating Nd-doped YF3 as a promising contactless luminescent thermometer.

A dinuclear cuprous chloride coordination polymer with grinding triggered luminescence enhancement and temperature dependent luminescent properties

A cuprous cluster-based luminescent coordination polymer [Cu(OPY)Cl]n (1, OPY ​= ​4,4′-(oxybis (4,1-phenylene))dipyridine) has been hydrothermally synthesized and structurally characterized. Compound 1 consists of bent butterfly dinuclear [Cu2Cl2] core and V-shaped OPY ligand, which exhibits a perpendicularly interpenetrated 2D ​+ ​2D → 3D structural characteristic. Compound 1 emits orange red luminescence originated from the dual-emitting behavior at room temperature in the solid state. Its photoluminescence properties have been fully studied and verified by time-dependent density functional theory (TD-DFT) calculations. In addition, the grinding and temperature dependent luminescence properties of 1 have also been investigated in detail.

Luminescence and optical properties of sodium germanate glasses doped with Sm3+ ions

Sm3+ doped sodium germanate glasses were synthesized by high temperature melt-quenching technique, suitable glass composition with optimum Sm3+ concentration and good luminescence thermal stability was obtained. The luminescence performance of Sm3+ and its optical transition property in glasses were studied. The optical transition intensity parameters of Sm3+ were calculated according to Judd-Ofelt theory. According to Huang's model and Dexter's model, it was confirmed that the electric dipole-dipole interaction among Sm3+ was responsible for the concentration dependent luminescence quenching of 4G5/2 level of Sm3+. Temperature dependent luminescence characteristics of Sm3+ was also investigated, and the luminescence thermal quenching behavior was found. When the temperature was 423 K, the emission intensity of the sample can still maintain 90% of that at room temperature. The result showed that this kind of red-emitting glass phosphor had an excellent luminescence thermal stability.

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

A Smart Molecule Showing Spin Crossover Responsive Aggregation-Induced Emission

Tailoring of strong orange-red-emitting materials for luminescence lifetime thermometry, anti-counterfeiting, and solid-state lighting applications

Strong orange-red-emitting Ba2LaTaO6:Eu3+ phosphors were designed and applied in various optical applications of luminescence lifetime thermometer, anti-counterfeiting film, and solid-state lighting applications. The crystal structure, elemental composition, asymmetry ratio, and other luminescent behaviors were investigated in detail. Especially, the optimal Ba2LaTaO6:0.1Eu3+ phosphor presented remarkable quantum yield (45.29%) and thermal stability (71.52% at 423 K). Based on the temperature-dependent luminescence decay curves, the maximum relative sensing sensitivity was 0.185 × 10−2 K−1 at 513 K. In addition, a novel anti-counterfeiting technique was introduced. The fabricated polydimethylsiloxane films exhibited three different colors under the irradiations of room light, 254 nm light, and 365 nm light, respectively. Eventually, the packaged light-emitting diode displayed the pure orange-red emission. Briefly, a series of the Eu3+-activated Ba2LaTaO6 phosphors with excellent luminescent properties were characterized and further applied in several optical fields for the first time.

Temperature quenching of Cr3+ in ASc(Si1-xGex)2O6 (A=Li/Na) solid solutions

Blue absorbing near infrared (NIR) emitting phosphors are a promising class of materials for phosphor converted NIR LEDs, which can be used in compact NIR spectrometers. Preferably, these phosphors have a broad emission spectrum and show negligible luminescence quenching at LED operating temperatures (100 °C). Here, we investigated ASc(Si1-xGex)2O6 (A = Li/Na, x = 0,0.2,0.4,0.6,0.8,1) solid solutions doped with Cr3+ to tune and optimize the emission maximum and bandwidth to cover the full 700–1100 nm range. With increasing Ge content an emission redshift was observed, along with emission band broadening at intermediate Ge/Si ratio, which is explained by disorder around Cr3+ in the second coordination sphere (mixed Si/Ge). Temperature dependent emission spectra and luminescence decay curves were measured between 90 K and 670 K to determine the quenching temperature TQ. With increasing Ge content TQ drops from 550 K to below 400 K. Interestingly, Cr3+ emission in the highly symmetric site in LiScSi2O6 shows a strongly temperature dependent lifetime before thermal quenching sets in. DFT calculations on LiScSi2O6 indicate that asymmetric vibrations at the Sc site are involved and calculated phonon energies were confirmed by measuring FTIR. Our study indicates that a solid solution is a promising way to increase the emission bandwidth. However, with increasing Ge content TQ decreases. An optimum Ge-content in LiSc(Si1-xGex)2O6:Cr3+ is x = 0.2–0.4 as it redshifts the NIR band maximum close to 900 nm and offers a FWHM bandwidth around 180 nm, while keeping the thermal quenching temperature high enough for application in NIR-LEDs.

Temperature-dependent luminescence of Bi3+, Eu3+ co-activated La2MgGeO6 phosphor for dual-mode optical thermometry

Using a high-temperature solid-phase method, a series of La2MgGeO6: Bi3+, Eu3+ samples with different doping amounts of Bi3+ and Eu3+ were obtained. The crystal structure, morphology, luminescence characteristics, temperature-varying luminescence spectrum, fluorescence attenuation curve, and energy transfer mechanism of the samples were explored. In La2MgGeO6: Bi3+, Eu3+ phosphors, Bi3+ and Eu3+ ions occupy the La3+ ion position. Under ultraviolet (UV) excitation, the emission spectra of LMGO: Bi3+ and the excitation spectra of LMGO: Eu3+ have significant spectral overlap, indicating that there is energy transfer between Bi3+ and Eu3+. By adjusting the doping amounts of Eu3+, adjustable luminescence can be obtained in the co-doped samples. According to the varying temperature-dependence trends of Bi3+ and Eu3+ ions, fluorescence intensity ratio technology was used to explore the temperature-sensing characteristics of Bi3+ and Eu3+ ions. The maximum absolute sensitivity and relative sensitivity were 0.074%·K−1 and 2.389%·K−1, respectively. In addition, by monitoring the lifetime decay time of Bi3+ with temperature, the maximum temperature sensitivity of the La2MgGeO6: Bi3+ samples was 4.09%·K−1. The above results indicate that La2MgGeO6: Bi3+, Eu3+ samples can be used as potential luminescent materials for temperature detection.

Experimental and Theoretical Studies of the Site Occupancy and Luminescence of Ce3+ in LiSr4(BO3)3 for Potential X-ray Detecting Applications.

Ce3+-doped LiSr4(BO3)3 phosphors have been prepared by a high-temperature solid-state reaction method, and structural refinement of the host compound has been performed. The excitation and emission spectra in the vacuum ultraviolet-ultraviolet-visible range at cryogenic temperatures reveal that Ce3+ ions preferentially occupy eight-coordinated Sr2+ sites in LiSr4(BO3)3. Such experimental attribution is well corroborated by the calculated 4f-5d transition energies and defect formation energies of Ce3+ ions at two distinct Sr2+ sites in the first-principles framework. In addition, the doping concentration-dependent luminescence and the temperature-dependent luminescence are systematically investigated by luminescence intensity and lifetime measurements, respectively. This shows that concentration quenching does not occur in the investigated doping range, but inhomogeneous broadening exists in the concentrated samples. With the estimated thermal quenching activation energy, the discussions on the thermal quenching mechanisms suggest that the thermal-ionization process of the 5d electron is a dominant channel for thermal quenching of Ce3+ luminescence, despite the fact that thermally activated concentration quenching cannot be excluded for the highly doped samples. Finally, the X-ray excited luminescence measurement demonstrates the promising applications of the phosphors in X-ray detection.

A novel blue-light excitable Pr3+ doped (Sr,Ba)LaMgTaO6 phosphor for plant growth lighting

In this work, a series of Pr3+ ions doped (Sr,Ba)LaMgTaO6 phosphors were prepared and applied for plant growth lighting. Under 450 nm excitation, (Sr,Ba)LaMgTaO6:Pr3+ exhibits intense reddish emission at around 650 nm which is assigned to the 3P0→3F2 transition of Pr3+ ions. The luminescence intensity reaches to the maximum at 2.5 mol% Pr3+ doping content both in SrLaMgTaO6:Pr3+ and BaLaMgTaO6:Pr3+ systems. Meanwhile, the internal quantum efficiency (IQE) test shows that the IQE of the SrLaMgTaO6:0.025Pr3+ phosphor is 33.34% upon blue light excitation. The decay curves and temperature-dependent luminescence measurements of the (Sr,Ba)LaMgTaO6:Pr3+ phosphors were performed and investigated in detail. The red light emitting diodes (LEDs) were packaged using the SrLaMgTaO6:Pr3+ and BaLaMgTaO6:Pr3+ phosphors combined with a blue LED chip, which are well-overlapped with the absorption band of photosynthesis. Results indicate that the (Sr,Ba)LaMgTaO6:Pr3+ can serve as a component of the red light in plant-growth LEDs.

Site Occupancies, Electron-Vibration Interaction and Energy Transfer of CaMgSi2 O6 : Eu2+ , Mn2+ Phosphors for Potential Temperature-Sensing and Anti-counterfeiting Applications.

Eu2+ -, Mn2+ - and Eu2+ -Mn2+ -doped CaMgSi2 O6 phosphors have been prepared by a high-temperature solid-state reaction. Systematic investigation of the concentration- and temperature-dependent luminescence of Mn2+ showed that Mn2+ ions occupy two distinct sites in CaMgSi2 O6 . Electron-vibration interaction (EVI) analyses of Mn2+ ions revealed Huang-Rhys factors of 4.73 and 2.82 as well as effective phonon energies of 313 and 383 cm-1 for the two sites. Eu2+ -Mn2+ energy transfer is also discussed, and its efficiency is estimated by lifetime and luminescence spectra. The different thermal quenching behaviours of Eu2+ and Mn2+ , the distinct emission colours of Eu2+ (blue, band peak at ∼451 nm) and Mn2+ (yellow-red range, band peaks at ∼583 and 693 nm) endow the co-doped samples with potential applications in luminescence thermometry and temperature-/excitation wavelength-responsive dual anti-counterfeiting.

Sensitive and Reliable Fluorescent Thermometer Based on a Red-Emitting Li2MgHfO4:Mn4+ Phosphor.

Contactless fluorescent thermometers are rapidly gaining popularity due to their sensitivity and flexibility. However, the development of sensitive and reliable non-rare-earth-containing fluorescent thermometers remains a significant challenge. Here, a new rare-earth-free, red-emitting phosphor, Li2MgHfO4:Mn4+, was developed for temperature sensing. An experimental analysis combined with density functional theory and crystal field calculations reveals that the sensitive temperature-dependent luminescence arises from nonradiative transitions induced by lattice vibration. Li2MgHfO4:Mn4+ also exhibits reliable recovery performance after 100 heating-cooling cycles due to the elimination of surface defects, which is rare but vital for practical application. This study puts forward a new design strategy for fluorescent thermometers and sheds light on the fundamental structure-property relationships that guide sensitive temperature-dependent luminescence. These considerations are crucial for developing next-generation fluorescence-based thermometers.

Green Synthesis of Deep Ultraviolet Response Nanophosphors with Tunable Full-visible-spectra Emission for Luminescent Temperature Sensing

Background: Recently, the CaMoO4 nanocrystal has been viewed as one of the most promising substrates for rare-earth-doped nanophosphors due to its high density, stable chemical properties, and good deep-ultraviolet (DUV) responding characteristics. Aim: In this work, a green synthesis approach is proposed to obtain rare-earth-doped CaMoO4 nanodispersion with full-visible-spectra emission by using an ethanol-water mixed solvent in a rotating packed bed (RPB) reactor. Method: The obtained nanophosphors exhibited bright luminescent emission with tunable color in the range of full-visible-spectra via doping of Eu3+, Tb3+, and Dy3+, when they were excited by deepultraviolet (DUV) light. The RPB promoted the uniform distribution of rare-earth ions and the crystallinity of CaMoO4 particles, and the use of ethanol-water as solvents with no toxicity and less environmental pollution was beneficial for large-scale production. Result: The quantum yields for nanophosphors of CaMoO4: Na+, Eu3+, CaMoO4: Na+, Tb3+, and Ca- MoO4: Na+, Dy3+ were measured to be 46.96 %, 28.05 %, and 10.27 %, respectively, which were among the highest values ever reported for rare-earth-doped CaMoO4-based nanophosphors with similar morphology. The temperature-dependent luminescence of CaMoO4: Eu3+, Na+ nanophosphors was investigated in the range of 298 K - 498 K. Conclusion: The clear correlation between luminescence intensity and temperature indicates the potential novel application areas for CaMoO4: Na+, Eu3+ nanophosphor as a non-invasive thermometer. Upon regulating different nanophosphor material ratios, the obtained product shows a flexible fluorescence towards full-visible-spectra emission.

Impact of Noise and Background on Measurement Uncertainties in Luminescence Thermometry.

Materials with temperature-dependent luminescence can be used as local thermometers when incorporated in, for example, a biological environment or chemical reactor. Researchers have continuously developed new materials aiming for the highest sensitivity of luminescence to temperature. Although the comparison of luminescent materials based on their temperature sensitivity is convenient, this parameter gives an incomplete description of the potential performance of the materials in applications. Here, we demonstrate how the precision of a temperature measurement with luminescent nanocrystals depends not only on the temperature sensitivity of the nanocrystals but also on their luminescence strength compared to measurement noise and background signal. After first determining the noise characteristics of our instrumentation, we show how the uncertainty of a temperature measurement can be predicted quantitatively. Our predictions match the temperature uncertainties that we extract from repeated measurements, over a wide temperature range (303–473 K), for different CCD readout settings, and for different background levels. The work presented here is the first study that incorporates all of these practical issues to accurately calculate the uncertainty of luminescent nanothermometers. This method will be important for the optimization and development of luminescent nanothermometers.

Tunable Fluorescence and Afterglow in Organic Crystals for Temperature Sensing.

The modulation of the properties of emission from multiple emission states in a single-component organic luminescent material is highly desirable in data anticounterfeiting, information storage, and bioapplications. Here, a single-component luminescent organic crystal of difluoroboron diphenyl β-diketonate with controllable multiple emission colors is successfully reported. The temperature-dependent luminescence experiments supported by high-level theoretical calculations demonstrate that the ratio of the fluorescence between the monomer and excimer and the phosphorescence maxima of the excimer can be effectively regulated. In addition, the temperature-dependent fluorescence and afterglow dual-emission color changes provide a new strategy for the design of highly accurate double-checked temperature sensors.

Role of energy transfer on the luminescent performance of UV light driven Er3+/Dy3+ co-activated fluoroborosilicate glasses

In this work, authors systematically investigates the role of Er3+→Dy3+ energy transfer (ET) on the luminescent characteristics of UV-excited Er3+/Dy3+ co-activated fluoroborosilicate glasses via spectral overlying diagram, photoluminescence excitation, emission and decay analyses, temperature dependent luminescence and quantum efficiency measurements. The concentration dependent quenching of Er3+ luminescence intensity with respect to the enhancement in Dy3+ emission bands envisages the ET from Erbium to Dysprosium under 379 nm excitation and is further affirmed through the increased ET efficiency (49.6%) estimated from the lifetime values. Evaluated CIE colorimetry analyses recommend the as-prepared material for photonic applications.

Giant Ln 30 -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Giant Ln ₃₀ -Cluster-Embedded Polyoxotungstate Nanoclusters with Exceptional Proton-Conducting and Luminescent Properties

Электрон-фононное взаимодействие в композитах с колллоидными квантовыми точками: исследование методами люминесцентной спектроскопии и комбинационного рассеяния света

The temperature-dependent luminescence spectra were analyzed to determine the parameters of the electron-phonon interaction (Huang-Rhys factor and the average phonon energy) for nanocomposites with colloidal CdSe/CdS/ZnS quantum dots (deposited on the surface of a glass substrate and embedded in a thin polymer film of polyisobutylene, and in a frozen colloidal solution in toluene). The measured values of the parameters are analyzed in comparison with model calculations and data obtained using the low-frequency Raman spectroscopy. It is found that in the case of a vitrified colloidal solution of quantum dots in toluene, the matrix effect leads to a noticeable change in the parameters of the electron-phonon interaction.