Investigation on the Fluorescence Intensity Ratio Sensing Thermometry Based on Nonthermally Coupled Levels

The Art of Nanoparticle Design: Unconventional Morphologies for Advancing Luminescent Technologies

The advanced design of rare-earth-doped (RE-doped) fluoride nanoparticles has expanded their applications ranging from anticounterfeiting luminescence and contactless temperature measurement to photodynamic therapy. Several recent studies have focused on developing rare morphologies of RE-doped nanoparticles. Distinct physical morphologies of RE-doped fluoride materials set them apart from contemporary nanoparticles. Every unusual structure holds the potential to dramatically improve the physical performance of nanoparticles, resulting in a remarkable revolution and a wide range of applications. This comprehensive review serves as a guide offering insights into various uniquely structured nanoparticles, including hollow, dumbbell-shaped, and peasecod-like forms. It aims to cater to both novices and experts interested in exploring the morphological transformations of nanoparticles. Discovering new energy transfer pathways and enhancing the optical application performance have been long-term challenges for which new solutions can be found in old papers. In the future, nanoparticle morphology design is expected to involve more refined microphysical methods and chemically-induced syntheses. Targeted modification of nanoparticle morphology and the aggregation of nanoparticles of various shapes can provide the advantages of different structures and enhance the universality of nanoparticles.

Multifunctional Optical Sensing with Lanthanide-Doped Upconverting Nanomaterials: Improving Detection Performance of Temperature and Pressure in the Visible and NIR Ranges

Temperature and pressure are fundamental physical parameters in the field of materials science, making their monitoring of utmost significance for scientists and engineers. Here, the NaSrY(MoO4)3:0.02Er3+/0.01Tm3+/0.15Yb3+ nanophosphor is developed as an optical sensor material. Under 975 nm laser excitation, the upconversion characteristics and optical detection performance of the multifunctional sensing platform of temperature and pressure (vacuum) are investigated. We have successfully developed a novel detection platform that enables optical detection of pressure (vacuum) and temperature. This platform utilizes thermally coupled levels (TCLs) and non-TCLs of Er3+ and Tm3+ to achieve ratiometric detection. The multimodal optical temperature and pressure detection based on TCLs and non-TCLs is successfully realized by using different emission bands of double emission centers, which makes it possible for self-referencing optical temperature and pressure measurement modes. These results indicate that the developed nanophosphor is a promising candidate for optical sensors, and our findings suggest potential strategies for modulating the sensor properties of luminescent materials doped with rare-earth ions.

Ultralow pressure sensing and luminescence thermometry based on the emissions of Er3+/Yb3+ codoped Y2Mo4O15 phosphors

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature.

Boltzmann- and Non-Boltzmann-Based Thermometers in the First, Second and Third Biological Windows for the SrF2:Yb3+, Ho3+ Nanocrystals Under 980, 940 and 915 nm Excitations

Spectrally determination of temperature based on the lanthanide-doped nanocrystals (NCs) is a vital strategy to noninvasively measure the temperature in practical applications. Here, we synthesized a series of SrF₂:Yb³⁺/Ho³⁺ NCs and simultaneously observed the efficient visible upconversion luminescence (UCL) and near-infrared (NIR) downconversion luminescence (DCL) under 980, 940 and 915 nm excitations. Subsequently, these NCs were further utilized for thermometers based on the Boltzmann (thermally coupled levels, TCLs) and non-Boltzmann (non-thermally coupled levels, NTCLs) of Ho³⁺ ions in the first (~ 650 nm), second (~ 1012 nm) and third (~ 2020 nm) biological windows (BW-I, BW-II and BW-III) under tri-wavelength excitations. The thermometric parameters including the relative sensitivity ([Formula: see text]) and temperature uncertainty ([Formula: see text]) are quantitatively determined on the I₆₄₈/I₅₄₁ (BW-I), I₁₁₈₆/I₁₀₁₂ (BW-II), and I₁₉₅₀/I₂₀₂₀ (BW-III) transitions of Ho³⁺ ions in the temperature range of 303-573 K. Comparative experimental results demonstrated that the thermometer has superior performances.

Ratiometric thermometry using single Er3+-doped CaWO4phosphors

Single doped CaWO₄:Er³⁺phosphors were synthesized and studied for application of optical thermal sensing within a wide range of 98-773 K. Ratiometric strategy utilizing two luminescence intensity ratios, one between host and Er³⁺band (LIR₁) and second between different Er³⁺transitions (LIR₂), results in self-referencing temperature readouts. The presence of two temperature-dependent parameters could improve thermometric characteristics and broaden the working temperature range compared to a usual single-parameter thermometer. Thermometric performances of prepared samples were evaluated in terms of thermal sensitivities, temperature resolution and repeatability. The highest sensitivity of 2.09% K^-1@300 K was found for LIR₁, whereas LIR₂provided more accurate thermal sensing with a temperature resolution of 0.06-0.1 K. Effect of Er³⁺doping concentration on sensing properties were studied. The presented findings indicate that CaWO₄:Er³⁺phosphors are perspective in dual-mode thermal sensing with high sensitivity and sub-degree resolution.

Constructing high sensitivity thermometry with dual-emitting Nd3+/Er3+/Yb3+ codoped BaWO4 single crystal material

Inorganic oxides doped with rear earth(RE) have attracted much interest because of their outstanding optical properties. In this paper, the BaWO₄:Yb³⁺/Er³⁺/Nd³⁺ phosphors were successfully prepared by typical solid state method. The crystalline structure of the samples was characterized through X-ray diffraction(XRD). The morphology of that was demonstrated with field emission scanning electron microscopy(FE-SEM). Under 980 nm excitation, the BaWO₄: Yb³⁺/Er³⁺/Nd³⁺ phosphor presented four typical emissions at green(524-550 nm, Er³⁺), red(∼655 nm, Er³⁺), near infrared(∼710 nm, ∼820 nm, Nd³⁺). Furthermore, the temperature sensing properties of the samples were investigated in the temperature range of 303-573 K. The fluorescence intensity ratio(FIR) technique based on thermal and non-thermal coupled levels was applied to analyse the sensing performances. For BaWO₄:Yb³⁺/Er³⁺/Nd³⁺ phosphor, the maximum absolute sensitivity reached 0.0423 K^-1 at 303 K, which is based on ²H_11/2(Er³⁺) and ⁴F_7/2(Nd³⁺) levels. The repeatability of temperature response also was proved through four cold and heat cycles. The above result indicated that the BaWO₄:Yb³⁺/Er³⁺/Nd³⁺ phosphor would be a promising temperature sensing materials.

Compensation effect of electron traps for enhanced fluorescence intensity ratio thermometry performance

How the electron traps in the host matrix impact the fluorescence intensity ratio (FIR) thermometry performance in inorganic phosphors is still unclear. In this work, the relationships between temperature-dependent photoluminescence,...

Double-doped YVO4 nanoparticles as optical dual-center ratiometric thermometers

Crystalline inorganic nanoparticles doped with rare earth ions are widely used in variety of scientific and industry applications due to the unique spectroscopic properties. Temperature dependence of their luminescence parameters...

Enhancing the Upconversion Luminescence and Sensitivity of Nanothermometry through Advanced Design of Dumbbell-Shaped Structured Nanoparticles

The core-shell engineering of lanthanide-doped nanoparticles has captured considerable attention because it can safeguard the luminescence intensity of the core by reducing surface defects. However, the limited surface area of the traditional spherical core-shell structure hinders the further breakthrough of the brightness. Herein, a unique NaYF₄:Yb³⁺/RE³⁺@NaYF₄:Yb³⁺/RE³⁺@NaNdF₄:Yb³⁺ (RE³⁺ = Ho³⁺ or Er³⁺) dumbbell-shaped multilayer nanoparticle featuring a high surface area is reported. Its upconversion luminescence intensity is higher than that of the conventional spherical core-shell structure. A thorough investigation is performed on the luminescence and thermometric mechanisms of Ho³⁺/Er³⁺ distributed in the core and the first shell. Remarkably, when Ho³⁺/Er³⁺ ions are distributed in the first shell, the relative sensitivity of the biological luminescence nanothermometer composed of downshifting near-infrared emissions is increased to 2.543% K^-1 (328 K), which considerably exceeds most reported values. The increased value is attributed to the more thermal-sensitive phonon-assisted energy transfer. For potential biological applications, dumbbell-shaped nanoparticles (DSNPs) with hydrophilic modification show excellent thermometric performance and high tissue penetration depth. Overall, the insights provided by this work will broaden the scope of novel DSNPs in the fields of luminescence and nanothermometry.

Enhanced upconversion red light emission of TiO2:Yb,Er thin film via Mn doping

TiO₂:Yb,Er films with different concentrations of Mn²⁺ are grown on SiO₂ glass substrates by pulsed laser deposition. It is found that the introduction of Mn²⁺ enhanced the intensity of upconversion emission. In particular, TiO₂:Yb,Er thin film with 5% Mn²⁺ ions exhibits the brightest upconversion emission. The upconversion red emission intensity is increased by 2.5-fold than that of a TiO₂:Yb,Er thin film without Mn²⁺ ions, which is ascribed to the multi-photon absorption and efficient exchange-energy transfer process between Er³⁺ and Mn²⁺. The high transmittance and good conductivity of the films made them possible to act as electron transport layer in solar cells.

The design of dual-switch fluorescence intensity ratio thermometry with high sensitivity and thermochromism based on a combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement

Currently, the temperature sensing performances of inorganic photoluminescence materials based on fluorescence intensity ratio technology have become a research hotspot in the optical thermometry field due to their non-contact sensing, fast response and high stability. However, several problems have obstructed the development of optical temperature sensing materials, including low sensitivity and narrow temperature measurement ranges. In view of the above dilemma, a new optical thermometer La2Mo3O12:Yb3+,Pr3+ designed based on the combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement was developed. Under excitation at 450 nm, the thermometer can work in a range from 298 to 648 K and the relative sensitivity reaches as high as 2.000% K-1 at 648 K. Under excitation at 980 nm, the thermometer can sense temperature with a wide range from 298 to 748 K and the relative sensitivity reaches as high as 4.325% K-1 at 598 K. A dual-switch optical temperature sensing material with high-sensitivity and a wide temperature measurement range has been successfully developed. Our research design strategies will give inspiration to the research on multi-switch temperature sensing materials with high sensitivity and a wide temperature measurement range.

Improving the temperature-dependent sensitivity of Ca9Y(PO4)7:Ce3+,Mn2+ and g-C3N4 composite phosphors by mechanical mixing

Luminescent properties of CYPO:Ce³⁺,Mn²⁺/g-C₃N₄ at different temperatures under 318 nm excitation.

Temperature dependent molecular fluorescence of [Agm]n+ quantum clusters stabilized by phosphate glass networks

Molecule like silver quantum clusters ([Agm]n+ QCs) exhibit an ultrasmall size confinement resulting in efficient broadband fluorescence. However, free [Agm]n+ QCs are also chemically active, so their stabilization is required for practical applications. We report in this work a phosphate oxyfluoride glass network enabled stabilization strategy of [Agm]n+ QCs. A series of silver-doped P2O5-ZnF2-xAg glasses were prepared by a conventional melt-and-quench method. The NMR and XPS results reveal that two types of [P(O,F)4] tetrahedrons (Q1, Q2) form chain structures and Zn(iv) connects [P(O,F)4] chains into a 3-dimension network in the glasses. The frameworks with limited void spaces were designed to restrict the polymerization degree, m, of [Agm]n+ QCs; the negatively charged tetrahedrons were designed to restrict the charge, n, of [Agm]n+ QCs. Through optical and mass spectroscopy studies, silver quantum clusters, [Ag2]2+ and [Ag4]2+, were identified to be charge compensated by [ZnO4] tetrahedrons and surrounded with [P(O,F)4] complex anions. The fluorescence thus gives high quantum efficiencies of 55.2% and 83.4%, for P2O5-ZnF2-xAg glass stabilized [Ag2]2+ and [Ag4]2+ QCs, respectively. This further reveals that the peak fixed fluorescence of [Ag2]2+ and [Ag4]2+ can be described by molecular fluorescence mechanisms. These are parity-allowed singlet-singlet transitions (S1 → S0), parity-forbidden triplet-singlet transitions (T1 → S0) and intersystem crossings between singlets (S1) and triplets (T1). The phonon coupled intersystem crossing between singlets (S1) and triplets (T1) determines the phosphate stabilized [Ag4]2+ QCs to exhibit a series of temperature dependent fluorescence behaviors. These include fluorescence intensity (at 50-200 K), intensity ratio (FIR) (at 50-200 K), peak shift (at 100-300 K) and lifetime (at 300-450 K) with maximum sensitivities of 1.27% K-1, 0.94% K-1, 0.29% K-1 and 0.41% K-1, respectively. Therefore, phosphate stabilized [Ag4]2+ QCs can be applied as temperature sensing probes, especially at low temperatures (10-300 K) and for color-based visualized temperature sensors.