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.

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.

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.

The influence of dopant concentration on temperature dependent emission spectra in LiLa1-x-yEuxTbyP4O12 nanocrystals: toward rational design of highly-sensitive luminescent nanothermometers.

Luminescence nanothermometry is gaining great interest, and different excitation and readout schemes have been sought to improve temperature sensitivity and sensing range, or to simplify the readout. Although many up-conversion based nanothermometers have been studied, Tb(3+) and Eu(3+) doped systems have not been widely considered, so far. Herein, we report the synthesis of new LiLa1-x-yEuxTbyP4O12 nanocrystals for luminescent thermal sensing; their spectroscopic properties have been investigated in a wide range of compositions and temperatures. In particular, the impact of dopant concentration on energy transfer processes (such as energy transfer, back energy transfer, energy diffusion and cross relaxation) is presented in a quantitative manner, both experimentally and theoretically, which enables the intentional optimization of the composition to find the finest balance between temperature sensitive excitation and depletion phenomena, and thus, enhance the luminescent thermometry properties. The studied thermometers can be applied in as wide a temperature range as 77-600 K, where they demonstrate sensitivity up to 1% K(-1), which is the highest among the Tb(3+) and Eu(3+) doped inorganic phosphor based materials, to date.

Broadband anti-Stokes white emission of Sr2CeO4 nanocrystals induced by laser irradiation.

The laser induced white emission (LIWE) from Sr2CeO4 nanocrystals upon irradiation with a focused IR laser beam was investigated. It was observed to be a threshold phenomenon with its intensity increasing exponentially with the excitation power density. This process was investigated under double laser beam simultaneous excitation in the UV range leading to Stokes emission in the visible range and in the IR range leading to anti-Stokes LIWE. With increasing LIWE intensity, the Stokes emission intensity strongly decreased. The LIWE is accompanied by efficient photocurrent generation depending on laser excitation density followed by multiphoton absorption and ionization processes. Photoimpedance measurements showed a sharp increase of the dielectric constant by several orders of magnitude in the Sr2CeO4 nanocrystals during the LIWE process demonstrating a metallic-like behaviour. The mechanisms of LIWE include multiphoton absorption and ionization that lead to the creation of a coupled pair of Ce3+ and Ce4+ ions that allow for the intervalence charge transfer (IVCT) emission transitions in the white light range. A strong decrease of absorption band intensity of Sr2CeO4 with increasing LIWE intensity confirms the creation of (Ce3+, Ce4+) pairs.

Near infrared absorbing near infrared emitting highly-sensitive luminescent nanothermometer based on Nd(3+) to Yb(3+) energy transfer.

A new type of near infrared absorbing near infrared emitting (NANE) luminescent nanothermometer is presented, with a physical background that relies on efficient Nd(3+) to Yb(3+) energy transfer under 808 nm photo-excitation. The emission spectra of LiLa0.9-xNd0.1YbxP4O12 (x = 0.05, 0.1, 0.2, 0.3, 0.5) nanocrystals were measured in a wide 100-700 °C temperature range. The ratio between the Nd(3+) ((4)F3/2→(4)I9/2) and Yb(3+) ((2)F5/2→(2)F7/2) luminescence bands, and the thermometer sensitivity were found to be strongly dependent on the Yb(3+) concentration. These phenomenological relations were discussed in terms of the competition between three phenomena, namely (a) Nd(3+)→ Yb(3+) phonon assisted energy transfer, (b) Yb(3+)→ Nd(3+) back energy transfer and (c) energy diffusion between Yb(3+) ions. The highest sensitivity of the temperature measurement was found for x = 0.5 (LiLa0.4Nd0.1Yb0.5P4O12), which was equal to 4 × 10(-3) K(-1) at 330 K. In stark contrast to conventional approaches, the proposed phosphate host matrix allows for a high level of doping, and thus, owing to the negligible concentration quenching, the presented luminophores exhibit a high absorption cross section and bright emission. Moreover, such optical remote thermometers, whose excitation and emission wavelengths are weakly scattered or absorbed and fall into the optical transmission window of the skin, may therefore become a practical solution for biomedical applications, such as remote control of thermotherapy.

Influence of grain size on optical properties of Sr2CeO4 nanocrystals.

The absorption, excitation, and emission spectra of the Sr2CeO4 nanocrystals prepared by the modified sol-gel method were investigated. The impact of the average grain size of Sr2CeO4 nanocrystals on their optical properties was investigated. It was observed that with increasing the average grain size of Sr2CeO4 nanocrystals, the emission decay times decreased significantly. A similar behavior was observed for the emission quantum efficiencies and the Huang-Rhys factors. The grain size dependence of optical parameters of Sr2CeO4 nanocrystals was found well fitted by functions of the reciprocal of the grain diameter. It was shown that this dependence may be rationalized assuming that the correction for electric local field associated with effective refractive index affecting the spherical nanoparticle is governed by its shell.

Synthesis and up-conversion luminescence of Er(3+) and Y b(3+) codoped nanocrystalline tetra- (KLaP4O12) and pentaphosphates (LaP5O14).

The up-converting nanocrystals of KLa0.95Er0.05Y bxP4O12 and La0.95-xEr0.05Y bxP5O14 were prepared using co-precipitation method. The spectroscopic properties of these materials were investigated in a function of Y b(3+) concentration. The up-conversion emission, power dependence of emission intensities, and the luminescence decay times were investigated. It was found that the green to red and (2)H11/2 → (4)I15/2 to (4)S3/2 → (4)I15/2 emission intensity ratio were strongly affected by the Y b(3+) concentration. Moreover, the order of up-conversion emission and threshold power rises up with Y b(3+) concentration for (4)S3/2 → (4)I15/2 transition. The luminescence decay time of the (4)S3/2 → (4)I15/2 emission increases with Y b(3+) concentration while the (4)F9/2 → (4)I15/2 emission is independent of dopant concentration. The influence of the Y b(3+) concentration on the up-conversion emission intensities was discussed in terms of concentration dependent hetero looped photon avalanche process. A comparison of the up-conversion properties of KLa0.95Er0.05Y bxP4O12 and La0.95-xEr0.05Y bxP5O14 nanocrystals was presented.

Synthesis and luminescent properties of La(1-x)Nd(x)P5O14 nanocrystals.

La(1-x)Nd(x)P5O14 nanocrystals were synthesized using a coprecipitation method. Their structure and morphology were determined. The luminescence and excitation spectra of La(1-x)Nd(x)P5O14 nanocrystals were measured in the entire range of Nd(3+) concentration. It was found that the relative intensities of absorption transitions increased significantly with concentration due to the cooperative interactions. The effect of concentration on fluorescence transitions was investigated. It was found that the intensity of the (4)F3/2 → (4)I11/2 transition significantly increased with concentration relative to the resonant (4)F3/2 → (4)I9/2 transition almost three times due to strong reabsorption. The concentration quenching of fluorescence was discussed in terms of the Yokota-Tanimoto model.

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.

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.

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.

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.

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

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

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.

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.

White emission of lithium ytterbium tetraphosphate nanocrystals.

An efficient anti-Stokes white broadband emission induced by 976 nm laser diode in lithium ytterbium tetraphosphate (LiYbP4O12) nanocrystals was investigated. The emission occurs at room temperature and atmospheric pressure. Its intensity demonstrates an evident threshold dependence on the temperature and excitation density characteristic to avalanche process. The white emission is accompanied by very efficient photoconductivity characterized by microampere photocurrent which increases with the fourth order of applied incident light power (~P4). We show that this emission is critically dependent on temperature and increases significantly in vacuum. It is concluded that the anti-Stokes white emission is associated with theYb3+- CT luminescence.