The Butterfly Effect: Multifaceted Consequences of Sensitizer Concentration Change in Phase Transition-based Luminescent Thermometer of LiYO2:Er3+,Yb3.

In response to the ongoing quest for new, highly sensitive upconverting luminescent thermometers, this article introduces, for the first time, upconverting luminescent thermometers based on thermally induced structured phase transitions. As demonstrated, the transition from the low-temperature monoclinic to the high-temperature tetragonal structures of LiYO2:Yb3+,Er3+ induces multifaceted modification in the spectroscopic properties of the examined material, influencing the spectral positions of luminescence bands, energy gap values between thermally coupled energy levels, and the red-to-green emission intensities ratio. Moreover, as illustrated, both the color of the emitted light and the phase transition temperature (from 265 K, for LiYO2:Er3+, 1%Yb3+, to 180 K, for 10%Yb3+), and consequently, the thermometric parameters of the luminescent thermometer can be modulated by the concentration of Yb3+ sensitizer ions. Establishing a correlation between the phase transition temperature and the mismatch of ion radii between the host material and dopant ions allows for smooth adjustment of the thermometric performance of such a thermometer following specific application requirements. Three different thermometric approaches were investigated using thermally coupled levels (SR = 1.8%/K at 180 K for 1%Yb3+), green to red emission intensities ratio (SR = 1.5%/K at 305 K for 2%Yb3+), and single band ratiometric approach (SR = 2.5%/K at 240 K for 10%Yb3+). The thermally induced structural phase transition in LiYO2:Er3+,Yb3+ has enabled the development of multiple upconverting luminescent thermometers. This innovative approach opens avenues for advancing the field of luminescence thermometry, offering enhanced relative thermal sensitivity and adaptability for various applications.

Understanding the power of luminescence ratiometric thermal history indicators driven by phase transitions: the case of Eu3+ doped LaVO4.

Finding thermal history phosphors with high sensitivity and a consistent readout is required for reliable thermal history determination with high temperature resolution. This work presents a new thermal history phosphor based on the luminescence of Eu3+ ions in LaVO4 to meet these requirements. As demonstrated, raising the annealing temperature causes a structural phase transition from a low-temperature tetragonal phase to a high-temperature single-stranded phase. The associated change in the local point symmetry of the crystallographic site occupied by Eu3+ ions result in a significant decrease in the emission intensity ratio of the 5D0 → 7F2 band relative to the 5D0 → 7F1 band, which enables the development of the ratiometric thermal history phosphor with the relative sensitivity of 0.38% °C-1 at 800 °C. Its applicative potential for thermal history readout was proved in the proof-of-concept experiment.

The role of Nd3+ concentration in the modulation of the thermometric performance of Stokes/anti-Stokes luminescence thermometer in NaYF4:Nd3.

The growing popularity of luminescence thermometry observed in recent years is related to the high application potential of this technique. However, in order to use such materials in a real application, it is necessary to have a thorough understanding of the processes responsible for thermal changes in the shape of the emission spectrum of luminophores. In this work, we explain how the concentration of Nd3+ dopant ions affects the change in the thermometric parameters of a thermometer based on the ratio of Stokes (4F3/2 → 4I9/2) to anti-Stokes (4F7/2,4S3/2 → 4I9/2) emission intensities in NaYF4:Nd3+. It is shown that the spectral broadening of the 4I9/2 → 4F5/2, 2H9/2 absorption band observed for higher dopant ion concentrations enables the modulation of the relative sensitivity, usable temperature range, and uncertainty of temperature determination of such a luminescent thermometer.

Optical heating and luminescence thermometry combined in a Cr3+-doped YAl3(BO3)4.

The possibility of optical heating with simultaneous control of the generated light within a single phosphor is particularly attractive from the perspective of multiple applications. This motivates the search for new solutions to enable efficient optical heating. In response to these requirements, based on the high absorption cross-section of Cr3+ ions, the optical heater based on YAl3(BO3)4:Cr3+ exhibiting highly efficient heating is developed. At the same time, the emission intensity ratio of 2E(g) → 4A2(g) and 4T2(g) → 4A2(g) of Cr3+ bands, thanks to the monotonic temperature dependence, enables remote temperature readout of the phosphor using luminescence thermometry technique. The combination of these two functionalities within a single phosphor makes YAl3(BO3)4:Cr3+ a promising, self thermally controlled photothermal agent.

A single-band ratiometric luminescent thermometer based on tetrafluorides operating entirely in the infrared region.

Luminescence thermometry is a remote temperature measurement technique that relies on thermally induced changes in spectroscopic properties. Because of its great application potential, even under very demanding conditions where other techniques fail, it has attracted the attention of many researchers in recent years. Unfortunately, most of the existing luminescence thermometers are fraught with large inaccuracies and thus are not reliable enough to be applied in real and demanding applications. However, there is one of the most recent and very promising but insufficiently studied approaches to luminescence thermometry quantification - single-band ratiometric luminescence thermometry. It is based on the analysis of the luminescence intensity ratio of a single emission band being photoexcited in two ways, i.e. by ground (GSA) and excited (ESA) state absorption. It is characterized by high relative sensitivity to temperature changes as well as high measurement precision. However, because ESA-excited luminescence intensity can depend on the type and concentration of dopant ions or the properties of the host material, further more-detailed studies must be conducted to understand the impact of numerous photophysical processes on the relative sensitivity, temperature resolution and useful temperature range of SBR LTs. In this work, the effect of interionic interactions occurring through cross-relaxation on the thermometric properties of single-band ratiometric luminescent thermometers in NaYF4:Nd3+ and NaGdF4:Nd3+ was investigated and discussed. In contrast to the disadvantageous concentration quenching phenomenon that is typically observed at an increased content of dopants, the beneficial role of cross-relaxation in the enhancement of the signal-to-noise ratio of the ESA-excited luminescence at high temperatures was demonstrated. The maximum relative temperature sensitivity reached was equal to S R = 16.9% K-1 at 223 K for NaYF4:50%Nd3+ nanocrystals and its value remained above 1% K-1 throughout the whole analyzed temperature range from 223 K to 473 K.

Correction: A single-band ratiometric luminescent thermometer based on tetrafluorides operating entirely in the infrared region.

[This corrects the article DOI: 10.1039/D1NA00727K.].

Modulation of thermometric performance of single-band-ratiometric luminescent thermometers based on luminescence of Nd3+ activated tetrafluorides by size modification.

Due to a number of its advantages, luminescence thermometry has been a strongly developed strand of temperature metrology over a period of time. Although there are several different types of luminescent thermometers, recently attention has been focused on a new single-band ratiometric approach, which is based on the excited state absorption phenomenon. Nevertheless, since this process is nontrivial and has not been studied extensively in the context of thermometry to date, a number of studies are necessary to enable the intentional development of highly sensitive thermometers based on this method. One of the important aspects is to investigate the influence of material size and the associated occurrence of surface effects, which is considered in this work. In addition, the research in this paper has been extended to explore the aspect of host material composition. Accordingly, nanocrystals and microcrystals of ß-NaYF4:2%Nd3+, ß-NaGdF4:2%Nd3+, and LiGdF4:2%Nd3+ were investigated in this work. The influence of surface effects on thermometric parameters was proved, with special emphasis on the useful temperature range. Thus, by increasing the particle size, it was possible to intentionally extend the useful range by even more than 100 K.

Results of plasma radiative compression investigation in the PF-24 device operated with D2, Ar and (100%-x)D2+x%Ar mixtures obtained using the 5-phase Lee model code.

The article presents new results for plasma radiative compression in high-current discharges in the z-pinch configuration. The results are based on the 113 discharges performed in the plasma-focus PF-24 device operated with D2, Ar and (100%-x)D2+xAr mixtures, with Ar pressure fractions x ≈ 3-60% (mole fractions). The constant initial total pressure is about 2.9 mbar and the constant initial pressure of Ar is 1.2 mbar. Each experimental discharge was simulated individually using the 5-phase Lee model code to carry out the fitting procedure of the total discharge current waveform. The results from these 113 computed discharges fitted to the corresponding 113 experimental discharges show that the increase of the effective atomic number of the gas mixture increases the probability of occurrence of plasma radiative compression phenomenon. Relatively weak radiative compression was found for part of the discharges in 15-60% range of Ar mole fractions and in Ar, while the stronger radiative compression occurred for part of discharges in Ar only. This is because there was too little total x-ray line radiation emission during the equilibrium pinch lifetime related to the very small amount of swept up mass and the low current flow through pinched plasma, represented by the decreasing values of model parameters as the Ar mole fraction increases. The results show that the main pinch parameters influencing the occurrence and strength of radiative compression are: total x-ray line emission yield, effective atomic number, initial pinch radius, initial pinch ion number density and initial pinch ion/electron temperature.

Correlation between the Covalency and the Thermometric Properties of Yb3+/Er3+ Codoped Nanocrystalline Orthophosphates.

Lanthanide-doped NaYF4 nanoparticles are most frequently studied host materials for numerous biomedical applications. Although efficient upconversion can be obtained in fluoride nanomaterials and good homogeneity of size and morphology is achieved, they are not very predestined for extensive material optimization toward enhanced features and functions. Here, we study the impact of rare-earth metals RE = Y, Lu, La, and Gd ions within Yb3+/Er3+ codoped nanocrystalline REPO4 orthophosphates. The enhanced luminescent thermometry features were found to be in relation to the covalency of RE3+-O2- bonds being modulated by these optically inactive rare-earth ion substitutes. Up to 30% relative sensitivity enhancement was found (from ca. 3.0 to ca. 3.8%/K at -150 °C) by purposefully increasing the covalence of the RE3+-O2- bond. These studies form the basis for intentional optimization thermal couple-based luminescent thermometers such as Yb3+-Er3+ upconverting ratiometric thermometer.

NIR luminescence lifetime nanothermometry based on phonon assisted Yb3+-Nd3+ energy transfer.

Luminescence thermometry in biomedical sciences is a highly desirable, but also highly challenging and demanding technology. Numerous artifacts have been found during steady-state spectroscopy temperature quantification, such as ratiometric spectroscopy. Oppositely, the luminescence lifetime is considered as the most reliable indicator of temperature thermometry because this luminescent feature is not susceptible to sample properties or luminescence reabsorption by the nanothermometers themselves. Unfortunately, this type of thermometer is much less studied and known. Here, the thermometric properties of Yb3+ ions in Nd0.5RE0.4Yb0.1PO4 luminescent temperature probes were evaluated, aiming to design and optimize luminescence lifetime based nanothermometers. Temperature dependence of the luminescence lifetimes is induced by thermally activated phonon assisted energy transfer from the 2F5/2 state of Yb3+ ions to the 4F3/2 state of Nd3+ ions, which in turn is responsible for the significant quenching of the Yb3+:2F5/2 lifetime. It was also found that the thermal quenching and thus the relative sensitivity of the luminescent thermometer can be intentionally altered by the RE ions used (RE = Y, Lu, La, and Gd). The highest relative sensitivity was found to be S R = 1.22% K-1 at 355 K for Nd0.5Y0.4Yb0.1PO4 and it remains above 1% K-1 up to 500 K. The high sensitivity and reliable thermometric performance of Nd0.5La0.4Yb0.1PO4 were confirmed by the high reproducibility of the temperature readout and the temperature uncertainty being as low as δT = 0.05 K at 383 K.

Impact of Tb3+ ion concentration on the morphology, structure and photoluminescence of Gd2 O2 SO4 :Tb3+ phosphor obtained using thermal decomposition of sulfate hydrate.

Gadolinium oxysulfate doped with terbium (Gd2 O2 SO4 :Tb3+ ; 0.1, 1.0, and 10.0 mol%) materials were obtained using thermal decomposition from sulfate hydrate under a dynamic air atmosphere and between 1320-1400 K. The materials were characterized using Fourier transform infrared spectroscopy, thermogravimetric/derivative thermogravimetric investigations and X-ray powder diffraction patterns. The Tb2 O2 SO4 compound was obtained at 1300 K and was used to compare thermal stability and photoluminescence behaviour with that of Gd2 O2 SO4 :Tb3+ (0.1, 1.0, and 10.0 mol%). Magnetic susceptibility measurements indicated the presence of 15% Tb4+ phases within Tb2 O2 SO4 . The materials were excited at 377 nm and displayed green narrow lines with the strongest emission peak at 545.5 nm due to the 5 D4 →7 F5 transition of Tb3+ ions. Brightness of terbium-activated gadolinium oxysulfate phosphors was enhanced with increase in the concentration of Tb3+ . Detailed analysis of spectroscopic properties of materials under investigations revealed efficient Gd2 O2 SO4 to Tb3+ and Tb3+ to Tb3+ energy transfers. Increase in dopant concentration led to the enhancement of 5 D4 →7 FJ emission intensity and reduction of 5 D3 →7 FJ emission intensity via cross-relaxation mechanisms. Distribution of particle size was increased by controlling dopant concentration in the host lattice. Obtained results confirmed that these materials could be applied potentially in field emission display devices and light-emitting diodes.

Synthesis, Cytotoxicity Assessment and Optical Properties Characterization of Colloidal GdPO4:Mn2+, Eu3+ for High Sensitivity Luminescent Nanothermometers Operating in the Physiological Temperature Range.

Herein, a novel synthesis method of colloidal GdPO4:Mn2+,Eu3+ nanoparticles for luminescent nanothermometry is proposed. XRD, TEM, DLS, and zeta potential measurements confirmed the crystallographic purity and reproducible morphology of the obtained nanoparticles. The spectroscopic properties of GdPO4:Mn2+,Eu3+ with different amounts of Mn2+ and Eu3+ were analyzed in a physiological temperature range. It was found that GdPO4:1%Eu3+,10%Mn2+ nanoparticles revealed extraordinary performance for noncontact temperature sensing with relative sensitivity SR = 8.88%/°C at 32 °C. Furthermore, the biocompatibility and safety of GdPO4:15%Mn2+,1%Eu3+ was confirmed by cytotoxicity studies. These results indicated that colloidal GdPO4 doped with Mn2+ and Eu3+ is a very promising candidate as a luminescent nanothermometer for in vitro applications.

Engineering excited state absorption based nanothermometry for temperature sensing and imaging.

Current luminescence nanothermometry exploits either temperature dependent quenching, temperature dependent energy transfer or thermal equilibrium between two metastable emitting levels, which are quantified to convert spectral features into absolute temperature. Although widely used and feasible, these methods are not always reliable enough in terms of flexibility, optimum temperature operating range and often require relatively complicated and expensive detection instrumentation, which may hinder wider adoption of luminescence based nanothermometry in technology and biomedical sciences. Therefore, not only more sensitive, brighter and robust phosphors are sought, but also novel temperature sensing schemes, which may potentially simplify remote quantification and imaging of temperature. In this work, we demonstrate the concept of contactless temperature readout and 2D temperature mapping by using excited state absorption (ESA) process instead of conventional approach based on ground state absorption (GSA) combined with multi-colour emission. The analysis of the excitation spectra of LiLaP4O12:Eu3+ nanocrystalline powders in a wide temperature range confirmed that the probability of populating higher levels of the ground 7FJ multiplet increases at increased temperatures. The Single Band Ratiometric Luminescent Thermometry (SBR-LT) opens new possibilities and offers luminescent thermometry at single emission band (5D0 → 7F1) under different excitation lines (7F2,3,4 → 5D0). In consequence, technically simple, temperature range adjustable, fast and affordable optical temperature imaging can be performed with high sensitivity reaching over 2.17% per °C in an unprecedentedly wide temperature range from -150 to 400 °C.

Enhancing the sensitivity of a Nd3+,Yb3+:YVO4 nanocrystalline luminescent thermometer by host sensitization.

Numerous methods are known to improve the relative temperature sensitivity of luminescent thermometers. These methods include optimization of the host material, the size of the nanoparticles, the dopant ion type and concentration, or the excitation intensity and operation mode of the excitation source. Here we propose a new approach, which exploits temperature dependent host sensitized emission from Nd3+ and Yb3+ lanthanide ions in a YVO4 matrix. We found out that the emission ratio of these two activators strongly depends on temperature, the size of the nanocrystals and the relative dopant concentration. The novelty comes from the fact that CT → Nd3+ and CT → Yb3+ are temperature dependent, and therefore helps to double the relative temperature sensitivity from ∼0.12% K-1 up to 0.25% K-1 for the smallest nanocrystals. Based on the temperature dependent luminescence lifetimes of Nd3+ and Yb3+ activators, we also found out that Nd3+→ Yb3+ ET has 70-75% efficiency and is temperature dependent.

Spectroscopic properties of LaGaO3:V,Nd3+ nanocrystals as a potential luminescent thermometer.

In this work we present the spectroscopic properties of LaGaO3:V,Nd3+ nanocrystals, which have been successfully obtained by the Pechini method. This is the first study where vanadium ions were applied in a LaGaO3 lattice for a non-contact luminescent thermometer. It was found that vanadium ions in the LaGaO3 matrix appear in three oxidation states, namely V5+, V4+ and V3+. It was found that the relative emission intensities of various states of vanadium ions depend strongly on grain size and therefore the emission color of LaGaO3:V can be easily modulated via the annealing temperature. The spectroscopic properties of this material were investigated in a wide temperature range (-150-300 °C). It was found that in the case of V-singly doped nanocrystals, the V4+ ions, reveal the best temperature sensing performance with high relative sensitivity (S = 1.76% °C-1) and broad usable temperature range (-50-150 °C). The different rates of thermal luminescence quenching of the vanadium ions provide three forms of non-contact temperature sensor, namely LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+. The highest sensitivities were found to be 1% °C-1 (at -5 °C and 90 °C), 0.49% °C-1 (at -20 °C) and 1.44% °C-1 (at 75 °C) for LaGaO3:V5+,Nd3+, LaGaO3:V4+,Nd3+ and LaGaO3:V3+,Nd3+, respectively.

The influence of manganese concentration on the sensitivity of bandshape and lifetime luminescent thermometers based on Y3Al5O12:Mn3+,Mn4+,Nd3+ nanocrystals.

Luminescent thermometers based on transition metal and lanthanide ion codoped nanocrystals have become a group of non-contact thermometers which are gaining importance due to their high sensitivity upon temperature changes. Here we present two types of luminescent thermometers, namely, bandshape and lifetime temperature sensors based on Y3Al5O12:Mn3+,Mn4+,Nd3+ nanocrystals. Their ability for temperature sensing was investigated as a function of Mn concentration. It was found that both sensitivity and usable temperature range depend on the Mn concentration. The highest sensitivity (S = 2.69%/K) was found for the lifetime luminescent thermometer with 0.01%Mn concentration and its value is gradually reduced with Mn content. Similarly, in the case of the bandshape luminescent thermometer, the sensitivity decreases from 1.69%/K for 0.01%Mn to 0.54%/K for 1%Mn. On the other hand the usable temperature range extends with dopant concentration. The concentration effect on the temperature dependent optical parameters is discussed in terms of interionic interactions facilitated for shorter Mn-Mn distances.

EXPERIMENTAL AND MONTE CARLO INVESTIGATIONS OF BCF-12 SMALL­AREA PLASTIC SCINTILLATION DETECTORS FOR NEUTRON PINHOLE CAMERA.

Plastic organic scintillators such as the blue-emitting BCF-12 are versatile and inexpensive tools. Recently, BCF-12 scintillators have been foreseen for investigation of the spatial distribution of neutrons emitted from dense magnetized plasma. For this purpose, small-area (5 mm × 5 mm) detectors based on BCF-12 scintillation rods and Hamamatsu photomultiplier tubes were designed and constructed at the Institute of Nuclear Physics. They will be located inside the neutron pinhole camera of the PF-24 plasma focus device. Two different geometrical layouts and approaches to the construction of the scintillation element were tested. The aim of this work was to determine the efficiency of the detectors. For this purpose, the experimental investigations using a neutron generator and a Pu-Be source were combined with Monte Carlo computations using the Geant4 code.

Optimization of highly sensitive YAG:Cr3+,Nd3+ nanocrystal-based luminescent thermometer operating in an optical window of biological tissues.

Luminescent and temperature sensitive properties of YAG:Cr3+,Nd3+ nanocrystals were analyzed as a function of temperature, nanoparticle size, and excitation wavelength. Due to numerous temperature-dependent phenomena (e.g. Boltzmann population, thermal quenching, and inter-ion energy transfer) occurring in this phosphor, four different thermometer definitions were evaluated with the target to achieve a high sensitivity and broad temperature sensitivity range. Using a Cr3+ to Nd3+ emission intensity ratio, the highest 3.48% K-1 sensitivity was obtained in the physiological temperature range. However, high sensitivity was compromised by a narrow sensitivity range or vice versa. The knowledge of the excitation and temperature susceptibility mechanisms enabled wise selection of the spectral features found in luminescence spectra for a temperature readout, which enabled the preservation of relatively high temperature sensitivity (>1.2% K-1 max) and extended the temperature sensitivity range from 100 K to 850 K. The size of the nanophosphors had negligible impact on the performance of the studied materials.

Fourier transform infrared and Raman spectroscopy in the study of phase transitions in dipyrazolium iodide triiodide: Experimental and theoretical analysis.

The paper presents the Infrared and Raman spectra of the powdered [C3N2H5+]2[I-∙I3-] crystal at the temperature intervals of 11-270K, covering two low-temperature phase transitions: discontinuous at 182/188K (cooling/heating) and continuous at 254K. The research shows that the vibrational states of the pyrazolium cations change significantly during discontinuous phase transition (III→II), while the continuous nature of successive structural transformation is more subtle and displays an insignificant change in the temperature coefficient of numerous vibrations during the II→I PT at 254K. The spectacular changes at Raman spectra above 188K confirm a huge rebuilding of inorganic network from [I-∙I3-] to [I42-]. Additionally, a complete geometry optimization was carried out in the solid state in order to obtain minimum structures and bonding properties. The theoretical results correspond well with the experimental data. Moreover, the infrared spectrum in harmonic approximation was calculated, and a comparative vibrational analysis was performed. CRYSTAL09 vibrational results appear to be in a good agreement with the experimental ones.