Multifunctional Eu3+- and Er3+/Yb3+-doped GdVO4 nanoparticles synthesized by reverse micelle method

Building a highly concentration responsive optical thermometer via tunable electron transfer pathways supported by intervalence charge transfer states

The thermal-coupled levels (TCLs) of lanthanides have attracted great attention in the field of optical thermometer, offering an efficient method to achieve non-contect temperatuer feedback in complex environment. However, the iner 4f electrons are shielded, which becomes the core obstacle in improving the sensing performance. This issue is now circumvented by constructing an electron transfer pathway between Tm3+(1D2) and Eu3+(5D0) configurations. As a result, the electron transfer barrier is related to the relative temperature sensitivity, giving an insight into the modulation mechanism. Compared to the conventional TCLs systems, the relative temperature sensitivity of this strategy is highly concentration-responsive, increasing from 5.56 to 10.1 % K-1 as the Eu3+ molar concentration rises from 0.3 to 0.5 mol%. This work reveals the inner emission mechanism based on IVCT-supported emission mode, and presents the highly adjustability of sensing performance.

Toward Ultra-High Sensitivity Optical Thermometers and Bright Yellow LEDs Based on Phonon-Assisted Energy Transfer in Rare Earth-Doped La2ZnTiO6 Double Perovskite

Double perovskites, a class of ceramic oxides with unique crystal structures and diverse physical properties, show promise for various technological applications including solar cells, photodetectors, and light-emitting diodes (LEDs). Despite limited research on rare earth-doped double perovskites, leveraging their ultrahigh luminous efficiency to achieve bright yellow LED emission and addressing energy transfer challenges between Yb3+ and Nd3+ ions in double perovskite La2ZnTiO6 with moderate phonon energy are explored in this work. Through phonon-assisted energy transfer, an ultrasensitive optical thermometer covering a wide temperature range is developed by utilizing the different temperature responses of Er3+ emission in the visible light region and Nd3+ emission in the near-infrared region based on the luminescence intensity ratio (LIR). All the results demonstrate that the rare earth (Yb-Er, Yb-Nd, and Yb-Nd-Er)-doped La2ZnTiO6 phosphors can be effectively utilized for ultrabright LED illumination and ultrahigh sensitivity self-calibrated temperature sensing. This research underscores the significance of phonon-assisted energy transfer in improving material properties and provides valuable insights for the advancement of multifunctional materials.

Anomalous thermal activation of green upconversion luminescence in Yb/Er/ZnGdO self-assembled microflowers for high-sensitivity temperature detection

Non-contact optical temperature detection has shown a great promise in biological systems and microfluidics because of its outstanding spatial resolution, superior accuracy, and non-invasive nature. However, the thermal quenching of photoluminescence significantly hinders the practical applications of optical temperature probes. Herein, we report thermally enhanced green upconversion luminescence in Yb/Er/ZnGdO microflowers by a defect-assisted thermal distribution mechanism. A 1.6-fold enhancement in green emission was demonstrated as the temperature increased from 298 K to 558 K. Experimental results and dynamic analysis demonstrated that this behavior of thermally activating green upconversion luminescence originates from the emission loss compensation, which is attributed to thermally-induced energy transfer from defect levels to the green emitting level. In addition, the Yb/Er/ZnGdO microflowers can act as self-referenced radiometric optical thermometers. The ultrahigh absolute sensitivity of 1.61% K-1 and an excellent relative sensitivity of 15.5% K-1 based on the 4F9/2/2H11/2(2) level pair were synchronously achieved at room temperature. These findings provide a novel strategy for surmounting the thermal quenching luminescence, thereby greatly promoting the application of non-contact sensitive radiometric thermometers.

Neodymium-Doped Gadolinium Compounds as Infrared Emitters for Multimodal Imaging

This study aims to investigate the optical properties of multiple neodymium-doped gadolinium compounds as a means to examine their eligibility as optical probes for fluorescence imaging. GdVO4, GdPO4, GdAlO3, Gd2SiO5 and Gd3Ga5O12 (GGG) samples were synthesized through solid-state reactions with varying neodymium doping levels to compare their optical properties in great detail. The optimal doping concentration was generally found to be approximately 2%. Furthermore, the luminescence lifetime, which is a valuable parameter for time-gated imaging, was determined to range from 276 down to 14 µs for the highest doping concentrations, resulting from energy transfer and migration assisted decay.

Structure, Luminescence and Temperature Detection Capability of [C(NH2)3]M(HCOO)3 (M = Mg2+, Mn2+, Zn2+) Hybrid Organic-Inorganic Formate Perovskites Containing Cr3+ Ions

Metal-organic frameworks are of great interest to scientists from various fields. This group also includes organic-inorganic hybrids with a perovskite structure. Recently their structural, phonon, and luminescent properties have been paid much attention. However, a new way of characterization of these materials has become luminescence thermometry. Herein, we report the structure, luminescence, and temperature detection ability of formate organic-inorganic perovskite [C(NH₂)₃]M(HCOO)₃ (Mg²⁺, Mn²⁺, Zn²⁺) doped with Cr³⁺ ions. Crystal field strength (Dq/B) and Racah parameters were determined based on diffuse reflectance spectra. It was shown that Cr³⁺ ions are positioned in the intermediate crystal field or close to it with a Dq/B range of 2.29-2.41. The co-existence of the spin-forbidden and spin-allowed transitions of Cr³⁺ ions enable the proposal of an approach for remote readout of the temperature. The relative sensitivity (S_r) can be easily modified by sample composition and Cr³⁺ ions concentration. The luminescent thermometer based on the ²E/⁴T_2g transitions has the relative sensitivity S_r of 2.08%K^-1 at 90 K for [C(NH₂)₃]Mg(HCOO)₃: 1% Cr³⁺ and decrease to 1.20%K^-1 at 100 K and 1.08%K^-1 at 90 K for Mn²⁺ and Zn²⁺ analogs, respectively.

Luminescent materials with dual-mode excitation and tunable emission color for anti-counterfeiting applications

GdVO₄-based dual-mode phosphors were successfully synthesized via a hydrothermal approach. The X-ray diffraction analysis determined the tetragonal structure as well as I4₁/amd space group of products by comparing with a reference pattern no. ICDD #01-072-0277. The morphology of yielded phosphors was confirmed by transmission electron microscopy and scanning electron microscopy. Detailed spectroscopy analysis revealed tunable luminescence properties with an increasing Yb³⁺ content in series of GdVO₄: x% Yb³⁺, y% Tm³⁺, 5% Eu³⁺ (x = 5, 10, 15, 20; y = 0.1, 0.5, 1) phosphors. For Yb³⁺, Tm³⁺, and Eu³⁺- codoped phosphors we observed bands related to the ¹G₄ → ³H₆ and ¹G₄ → ³F₄ transitions of Tm³⁺ ions, occurred through the cooperative up-conversion mechanism, where two nearby Yb³⁺ ions were involved in near-infrared absorption. Moreover, the GdVO₄: 20% Yb³⁺, 0.5% Tm³⁺, 5% Eu³⁺ showed the most outstanding color tunability from red color (x = 0.6338, y = 0.3172) under UV to blue color (x = 0.2640, y = 0.1988) under NIR excitation, which can be applied in anti-counterfeiting activity.

Metal-Organic Framework Optical Thermometer Based on Cr3+ Ion Luminescence

Metal-organic frameworks with perovskite structures have recently attracted increasing attention due to their structural, optical, and phonon properties. Herein, we report the structural and luminescence studies of a series of six heterometallic perovskite-type metal-organic frameworks with the general formula [EA]₂NaCr_xAl_1-x(HCOO)₆, where x = 1, 0.78, 0.57, 0.30, 0.21, and 0. The diffuse reflectance spectral analysis provided valuable information, particularly on crystal field strength (Dq/B) and energy band gap (E_g). We showed that the Dq/B varies in the 2.33-2.76 range depending on the composition of the sample. Performed Raman, XRD, and lifetime decay analyses provided information on the relationship between those parameters and the chemical composition. We also performed the temperature-dependent luminescence studies within the 80-400 K range, which was the first attempt to use an organic-inorganic framework luminescence thermometer based solely on the luminescence of Cr³⁺ ions. The results showed a strong correlation between the surrounding temperature, composition, and spectroscopic properties, allowing one to design a temperature sensing model. The temperature-dependent luminescence of the Cr³⁺ ions makes the investigated materials promising candidates for noncontact thermometers.

Ultra-High-Sensitive Temperature Sensing Based on Er3+ and Yb3+ Co-Doped Lead-Free Double Perovskite Microcrystals

Fluorescence intensity ratio (FIR) thermometry, a new contactless temperature measurement, can achieve accurate measurements in a harsh environment. In this work, all-inorganic lead-free Cs₂AgInCl₆: Er-Yb and Cs₂AgBiCl₆: Er-Yb microcrystals emit bright green up-conversion emission, which are synthesized by precipitation at a low temperature (80 °C). In up-conversion emission, FIR of the ²H_11/2 → ⁴I_15/2 band to the ⁴S_3/2 → ⁴I_15/2 band exhibits temperature dependence, which can be used as the temperature measurement parameter, so-called FIR thermometry. Moreover, the theoretically accurate measurement range is from 100 to 600 K, achieving maximum absolute sensitivities from 0.0130 to 0.0113 K^-1, respectively. The principle of up-conversion and high sensitivity is well explained by calculating the partial density of states. Compared to the reported thermometry materials based on the FIR method, the prepared all-inorganic lead-free Cs₂AgInCl₆: Er-Yb and Cs₂AgBiCl₆: Er-Yb microcrystals show outstanding temperature measurement width and sensitivity, becoming a potential candidate for high-sensitivity optical temperature sensors.

Eu3+ Doped LaF3 -based Inorganic-organic Hybrid Nanostructured Materials for Broad-spectrum Excitation and Strong Photoluminescence

Inorganic-organic hybrid nanoparticles formed by lanthanide-doped nanostructures and organic ligands have been intensively studied, which could greatly increase their photoluminescence performance as a result of the energy transfer process from organic ligands to Ln³⁺ ions. However, the photoluminescence intensity and excitation spectral width are still quite limited on coordinating with a single type of organic ligand. In this work, Eu³⁺ -doped LaF₃ (LaF₃ :Eu³⁺ ) nanoparticles were prepared using hydrothermal method, which was then hybridized with benzoic acid and thenoyltrifluoroacetone to form the hybrid nanostructures. After that, the hybrid nanostructures were mixed with 2,2'-azobisisobutyronitrile and methyl methacrylate to prepare the composites. The sample obtained by hybridization and composite doping with 5% Eu³⁺ exhibited the best photoluminescence performance. The excitation peak width and luminescence intensity of the hybrid nanostructures were significantly increased. The excitation spectral width of the inorganic-organic mixed hybrid nanostructures was particularly enhanced, which covers the whole ultraviolet (UV) band region of solar light on earth. The prepared composites exhibited good optical properties.

Influence of Gd3+ doping concentration on the properties of Na(Y,Gd)F4:Yb3+, Tm3+ upconverting nanoparticles and their long-term aging behavior

We present a systematic study on the properties of Na(Y,Gd)F₄-based upconverting nanoparticles (UCNP) doped with 18% Yb³⁺, 2% Tm³⁺, and the influence of Gd³⁺ (10-50 mol% Gd³⁺). UCNP were synthesized via the solvothermal method and had a range of diameters within 13 and 50 nm. Structural and photophysical changes were monitored for the UCNP samples after a 24-month incubation period in dry phase and further redispersion. Structural characterization was performed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as dynamic light scattering (DLS), and the upconversion luminescence (UCL) studies were executed at various temperatures (from 4 to 295 K) using time-resolved and steady-state spectroscopy. An increase in the hexagonal lattice phase with the increase of Gd³⁺ content was found, although the cubic phase was prevalent in most samples. The Tm³⁺-luminescence intensity as well as the Tm³⁺-luminescence decay times peaked at the Gd³⁺ concentration of 30 mol%. Although the general upconverting luminescence properties of the nanoparticles were preserved, the 24-month incubation period lead to irreversible agglomeration of the UCNP and changes in luminescence band ratios and lifetimes.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Hybrid Hierarchical Heterostructures of Nanoceramic Phosphors as Imaging Agents for Multiplexing and Living Cancer Cells Translocation

Existing fluorescent labels used in life sciences are based on organic compounds with limited lifetime or on quantum dots which are either expensive or toxic and have low kinetic stability in biological environments. To address these challenges, luminescent nanomaterials have been conceived as hierarchical, core–shell structures with spherical morphology and highly controlled dimensions. These tailor-made nanophosphors incorporate Ln:YVO₄ nanoparticles (Ln = Eu(III) and Er(III)) as 50 nm cores and display intense and narrow emission maxima centered at ∼565 nm. These cores can be encapsulated in silica shells with highly controlled dimensions as well as functionalized with chitosan or PEG5000 to reduce nonspecific interactions with biomolecules in living cells. Confocal fluorescence microscopy in living prostate cancer cells confirmed the potential of these platforms to overcome the disadvantages of commercial fluorophores and their feasibility as labels for multiplexing, biosensing, and imaging in life science assays.

Vanadium-based nanomaterials for cancer diagnosis and treatment

In the past few decades, various vanadium compounds have displayed potential in cancer treatment. However, fast clearness in the body and possible toxicity of vanadium compounds has hindered their further development. Vanadium-based nanomaterials not only overcome these limitations, but take advantage of the internal properties of vanadium in photics and magnetics, which enable them as a multimodal platform for cancer diagnosis and treatment. In this paper, we first introduced the basic biological and pharmacological functions of vanadium compounds in treating cancer. Then, the synthesis routes of three vanadium-based nanomaterials were discussed, including vanadium oxides, 2D vanadium sulfides, carbides and nitrides: V_mX_n (X = S, C, N) and water-insoluble vanadium salts. Finally, we highlighted the applications of these vanadium-based nanomaterials as tumor therapeutic and diagnostic agents.

Comparison of Three Ratiometric Temperature Readings from the Er3+ Upconversion Emission

The emission of Er³⁺ provides three combinations of emission bands suitable for ratiometric luminescence thermometry. Two combinations utilize ratios of visible emissions (²H_11/2→⁴I_15/2 at 523 nm/ ⁴S_3/2→⁴I_15/2 at 542 nm and ⁴F_7/2→⁴I_15/2 at 485 nm/ ⁴S_3/2→⁴I_15/2 at 545 nm), while emissions from the third combination are located in near-infrared, e.g., in the first biological window (²H_11/2→⁴I_13/2 at 793 nm/ ⁴S_3/2→⁴I_13/2 at 840 nm). Herein, we aimed to compare thermometric performances of these three different ratiometric readouts on account of their relative sensitivities, resolutions, and repeatability of measurements. For this aim, we prepared Yb³⁺,Er³⁺:YF₃ nanopowders by oxide fluorination. The structure of the materials was confirmed by X-ray diffraction analysis and particle morphology was evaluated from FE-SEM measurements. Upconversion emission spectra were measured over the 293–473 K range upon excitation by 980 nm radiation. The obtained relative sensitivities on temperature for 523/542, 485/542, and 793/840 emission intensity ratios were 1.06 ± 0.02, 2.03 ± 0.23, and 0.98 ± 0.10%K⁻¹ with temperature resolutions of 0.3, 0.7, and 1.8 K, respectively. The study showed that the higher relative temperature sensitivity does not necessarily lead to the more precise temperature measurement and better resolution, since it may be compromised by a larger uncertainty in measurement of low-intensity emission bands.

Sextuple ratiometric thermometry based on 980-nm-upconverted green fluorescence of Er3+ ions in submicron crystals

980-nm-upconverted 530 and 550 nm Er³⁺ green fluorescence spectra of Er³⁺/Yb³⁺-codoped NaGd(WO₄)₂ submicron crystals were measured in the temperature range of 298-383 K. A sextuple ratiometric thermometry is proposed. It is established on the basis of six schemes of fluorescence intensity ratio (FIR) that considers three component peaks of the 530 nm emission band and two component peaks of the 550 nm emission band, which involve electronic transitions between two Stark sublevels of Er³⁺. The study shows that the phosphor shows strong green fluorescence, which is verified by measured quantum yield, and thermally stable spectral structure desired for the sextuple ratiometric thermometry. All of the six FIR schemes display highly efficient sensing performances with slightly different thermal sensitivities. Each scheme gives a temperature value and the six schemes give an averaged result. In parallel, we have also carried out an ex vivo experimental study on the temperature characteristics of the green fluorescence of the phosphor. Almost same results have been obtained, verifying biological applicability of the phosphor. The ex vivo experimental results also show that the sextuple thermometry increases considerably the accuracy and reliability of temperature measurement in comparison with the conventional intensity integration method.

Yolk–shell structured Bi2SiO5:Yb3+,Ln3+ (Ln = Er, Ho, Tm) upconversion nanophosphors for optical thermometry and solid-state lighting

Bi₂SiO₅:Yb³⁺,Er³⁺ yolk–shell nanophosphors have been successfully synthesized, which are expected to find important applications in optical thermometry and solid-state lighting.

High-sensitivity dual UV/NIR-excited luminescence thermometry by rare earth vanadate nanoparticles

High-crystallinity Ln³⁺-doped YVO₄ nanoparticles combine multiple emissions under dual UV/NIR excitation, promoting high performance self-referenced luminescence thermometry.

GdVO4:Eu3+,Bi3+ Nanoparticles as a Contrast Agent for MRI and Luminescence Bioimaging

With the development of multifunctional imaging, gadolinium (Gd)-bearing inorganic nanoparticles (NPs), which were doped with trivalent lanthanide (Ln3+), have been applied in magnetic resonance imaging (MRI) and optical imaging owing to their high payload of Gd3+ ions and specific optical characteristics. In this study, we chose GdVO4 codoped with Eu3+ and Bi3+ as the host material to generate a highly efficient contrast agent (CA) for MRI and long-term luminescence imaging. The new CA emits strong and stable luminescence because of its strong characteristic emissions, resulting from the energy-transfer process from the vanadate groups (VO4 3-) to the Eu3+ and Bi3+ dopants. Additionally, these NPs provided conspicuous T 1 and T 2 relaxation time-shortening characteristics, which result in MRI enhancement. GdVO4:Eu3+,Bi3+ NPs were tested on liver tumor-bearing nude mice, and showed improved liver tumor contrast in T 2-weighted MR images (T 2WI). The dual-modal imaging probe exhibited no cytotoxicity or organ toxicity, reflecting its excellent biocompatibility. Thus, GdVO4:Eu3+,Bi3+ has the potential to be used for bioassays in vitro and liver tumor targeting in vivo. The results reveal the great promise of using the designed GdVO4:Eu3+,Bi3+ NPs as luminescent and MRI dual-mode bioprobes for clinical bioimaging applications.

Plasmonic Heating of Nanostructures

The absorption of light by plasmonic nanostructures and their associated temperature increase are exquisitely sensitive to the shape and composition of the structure and to the wavelength of light. Therefore, much effort is put into synthesizing novel nanostructures for optimized interaction with the incident light. The successful synthesis and characterization of high quality and biocompatible plasmonic colloidal nanoparticles has fostered numerous and expanding applications, especially in biomedical contexts, where such particles are highly promising for general drug delivery and for tomorrow's cancer treatment. We review the thermoplasmonic properties of the most commonly used plasmonic nanoparticles, including solid or composite metallic nanoparticles of various dimensions and geometries. Common methods for synthesizing plasmonic particles are presented with the overall goal of providing the reader with a guide for designing or choosing nanostructures with optimal thermoplasmonic properties for a given application. Finally, the biocompatibility and biological tolerance of structures are critically discussed along with novel applications of plasmonic nanoparticles in the life sciences.

Photo-isomerization of azobenzene containing surfactants induced by near-infrared light using upconversion nanoparticles as mediator

Here we report on photo-isomerization of azobenzene containing surfactants induced during irradiation with near-infrared (NIR) light in the presence of upconversion nanoparticles (UCNPs) acting as mediator. The surfactant molecule consists of charged head group and hydrophobic tail with azobenzene group incorporated in alkyl chain. The azobenzene group can be reversible photo-isomerized between two states: trans- and cis- by irradiation with light of an appropriate wavelength. The trans-cis photo-isomerization is induced by UV light, while cis-trans isomerization proceeds either thermally in darkness, or can be accelerated by exposure to illumination with a longer wavelength typically in a blue/green range. We present the application of lanthanide doped UCNPs to successfully switch azobenzene containing surfactants from cis to trans conformation in bulk solution using NIR light. Using Tm³⁺ or Er³⁺ as activator ions, the UCNPs provide emissions in the spectral range of 450 nm  <  λ _em  <  480 nm (for Tm³⁺, three and four photon induced emission) or 525 nm  <  λ _em  <  545 nm (for Er³⁺, two photon induced emission), respectively. Especially for UCNPs containing Tm³⁺ a good overlap of the emissions with the absorption bands of the azobenzene is present. Under illumination of the surfactant solution with NIR light (λ _ex  =  976 nm) in the presence of the Tm³⁺-doped UCNPs, the relaxation time of cis-trans photo-isomerization was increased by almost 13 times compared to thermally induced isomerization. The influence of thermal heating due to the irradiation using NIR light was shown to be minor for solvents not absorbing in NIR spectral range (e.g. CHCl₃) in contrast to water, which shows a distinct absorption in the NIR.

Engineering efficient upconverting nanothermometers using Eu3+ ions

Upconversion nanothermometry combines the possibility of optically sensing temperatures in very small areas, such as microfluidic channels or on microelectronic chips, with a simple detection setup in the visible spectral range and reduced heat transfer after near-infrared (NIR) excitation. We propose a ratiometric strategy based on Eu³⁺ ion luminescence activated through upconversion processes. Yb³⁺ ions act as a sensitizer in the NIR region (980 nm), and energy is transferred to Tm³⁺ ions that in turn excite Eu³⁺ ions whose luminescence is shown to be thermally sensitive. Tridoped SrF₂:Yb³⁺,Tm³⁺,Eu³⁺ nanoparticles (average size of 17 nm) show a relative thermal sensitivity of 1.1% K^-1 at 25.0 °C, in the range of the best ones reported to date for Ln³⁺-based nanothermometers based on upconversion emission. The present nanoparticle design allows us to exploit upconversion of lanthanide ions that otherwise cannot be directly excited upon NIR excitation and that may provide operational wavelengths with a highly stable read out to fill the spectral gaps currently existing in upconversion-based nanothermometry.

The influence of Si4+ co-doping on the spectroscopic properties of β-NaCaPO4:Eu2+/Eu3+

A series of luminescent materials based on a sodium calcium phosphate matrix doped with europium and different concentrations of silicon ions was synthesized using the Pechini method.

An energy self-compensating phosphosilicate material applied to temperature sensors

For years, researchers have been exploring effective methods of sustaining the emission intensity of phosphors with increasing temperature by suppressing emission loss. In this work, we developed a multi-cationic site and lattice-distorted phosphosilicate phosphor, Ca₈Al₂P₆SiO₂₈:Ce, Eu. To obtain luminous-self-healing properties, we attempted to change the energy depths and density distributions of the traps to achieve self-suppression of emission loss by energy compensation from the traps or energy transfer between Ce³⁺ and Eu²⁺/Eu³⁺. The temperature-dependent emission spectra indicate that the luminescence of Ce³⁺ presents similar change trends in both single and co-doped samples. Meanwhile, the change trends of the Eu²⁺/Eu³⁺ emission intensities show obvious differences. Combined with the thermoluminescence curves, decay times, temperature-dependent fluorescence characteristics and cathodoluminescence spectra, we speculate that the traps play an important role in the luminescence of Ce³⁺ due to the smaller energy difference of the Ce³⁺ excited states and the conduction band. The abnormal luminescence of Eu²⁺/Eu³⁺ mainly results from the energy transfer of Ce³⁺ to Eu²⁺/Eu³⁺. For this phenomenon, a high thermal sensitive fluorescence intensity ratio is obtained in a broad temperature range, which implies that this material can be applied in temperature sensors.

For years, researchers have been exploring effective methods of sustaining the emission intensity of phosphors with increasing temperature by suppressing emission loss.

Upconversion thermometry: a new tool to measure the thermal resistance of nanoparticles

The rapid evolution in luminescence thermometry in the last few years gradually shifted the research from the fabrication of more sensitive nanoarchitectures towards the use of the technique as a tool for thermal bioimaging and for the unveiling of properties of the thermometers themselves and of their local surroundings, for example to evaluate heat transport at unprecedented small scales. In this work, we demonstrated that KLu(WO4)2:Ho3+,Tm3+ nanoparticles are able to combine controllable heat release and upconversion thermometry permitting to estimate its thermal resistance (in air), a key parameter to model the heat transfer at the nanoscale.

A novel strategy for thermometry based on the temperature-induced red shift of the charge transfer band edge

We report a novel strategy for optical temperature sensing using the temperature-induced red shift of the charge transfer band (CTB) edge of the VO₄^3- groups in GdVO₄:5% Sm³⁺. Excitation spectra were recorded at a series of temperatures ranging from 300 to 480 K. It is demonstrated that an excitation intensity of around 360 nm corresponding to the tail of the CTB and an excitation intensity of 407.6 nm corresponding to the ⁶H_5/2 → ⁴F_7/2 transition of Sm³⁺ exhibit opposite temperature dependence. Based on this, the relative sensitivity was obtained to be 3313/T² in our investigated temperature range, which is remarkable progress compared with the optical temperature sensors reported previously. We believe that this work broadens the pathway for the design of highly sensitive temperature sensing materials.

Effect of doping Ge into Y2O3:Ho,Yb on the green-to-red emission ratio and temperature sensing

The Ge-doped Y₂O₃:Ho,Yb phosphor tunes the G/R ratio, and the G/R ratio has a higher absolute temperature sensitivity.

Dispersing upconversion nanocrystals in PMMA microfiber: a novel methodology for temperature sensing

The synthesis of a β-NaYF₄:Yb³⁺/Tm³⁺ phosphor by a thermal decomposition method, focusing on the fabrication of microfibers by the co-doping of nanocrystals with PMMA solution.

Multifunctional GdVO4:Eu core–shell nanoparticles containing 225Ac for targeted alpha therapy and molecular imaging

Development of actinium-225 doped Gd_0.8Eu_0.2VO₄ core–shell nanoparticles as multifunctional platforms for multimodal molecular imaging and targeted radionuclide therapy.

Investigation of photoluminescence properties, Judd–Ofelt analysis, luminescence nanothermometry and optical heating behaviour of Er3+/Eu3+/Yb3+:NaZnPO4 nanophosphors

The Er³⁺/Eu³⁺/Yb³⁺:NaZnPO₄ nanophosphors can be used as temperature sensors and optical nano-heaters with significant sensor sensitivity.

A simple, compact, low-cost, highly efficient thermometer based on green fluorescence of Er3+/Yb3+-codoped NaYF4 microcrystals

We developed a highly efficient optical thermometer based on intensity ratio of upconversion green fluorescence of Er³⁺/Yb³⁺-codoped NaYF₄ microcrystals. The sensor consists simply of a 980nm laser diode, one narrow-band interference filter, two lenses, one Si-photocell and one multimeter, while being without use of spectrometer and additional electronics. The device not only has a simple, compact structure (hence a low cost), but also displays highly efficient sensing performance, characterized by large signal-to-noise ratio due to strong fluorescence intensity, high thermal resolution and sensitivity, which have the values 1.3K and 1.24×10^-2K^-1, respectively, at the physiological temperature 310K. The excellent sensing performance of the device was further confirmed by the results of the measurements repeated using a spectrometer. The thermometer is highly generalized that can be applied to other luminescent materials, and shows great potential for the physiological temperature sensing in biological tissues and cells.

Nanometer-scale luminescent thermometry in bovine embryos

Luminescent nanothermometry is a powerful tool that can precisely monitor temperature changes in animal embryos. Among the most sensitive nanoluminescent temperature sensors are fluorescent nanodiamonds (FNDs), having nitrogen-vacancy color centers, and lanthanide-ion-doped upconversion nanoparticles (UCNPs). Here, we investigate their use as nanothermometers inside bovine embryos. The motivation for using both FNDs and UCNPs to measure temperature is to avoid the question of sensor confusion by the local cellular environment. Specifically, by simultaneously measuring temperature using two different modalities having different physics, it is possible to greatly improve the measurement confidence, thereby directly addressing the recent controversy surrounding temperature measurements in living organisms.

Origin of the temperature-induced redshift of the charge transfer band of GdVO4

The charge transfer band (CTB) of the VO43- groups in vanadates shifts to longer wavelengths with increasing temperature. The origin of this temperature-induced redshift was explored by studying the temperature-dependent excitation and emission spectra of GdVO₄ ranging from 300 to 480 K. The influences of the thermal population and the decline of the charge transfer gap on the spectral shift were analyzed using the configurational coordinate diagram. We conclude that the thermal population of vibrational sublevels of the ground electronic energy level dominates the temperature-induced redshift of the CTB. Taking advantage of the redshift and the thermal quenching, a novel ratiometric temperature-sensing strategy was proposed. Drastic temperature dependence was achieved, indicating a promising candidate for an optical thermometer with high sensing performance.

Engineering water-tolerant core/shell upconversion nanoparticles for optical temperature sensing

Luminescence thermometry is a promising approach using upconversion nanoparticles (UCNPs) with a nanoscale regime in biological tissues. UCNPs are superior to conventional fluorescent markers, benefiting from their autofluorescence suppression and deep imaging in tissues. However, they are still limited by poor water solubility and weak upconversion luminescence intensity, especially at a small particle size. Recently, YVO₄:Er⁺³,Yb⁺³ nanoparticles have shown high efficiency upconversion (UC) luminescence in water at single-particle level and high contrast imaging in biological models. Typically, a 980-nm laser triggers the UC process in the UCNPs, which overlaps with maximum absorption of water molecules that are dominant in biological samples, resulting in biological tissues overheating and possible damaging. Interestingly, neodymium (Nd⁺³) possesses a large absorption cross section at the water low absorption band (808 nm), which can overcome overheating issues. In this Letter, we introduce Nd⁺³ as a new near-infrared absorber and UC sensitizer into YVO₄:Er⁺³,Yb⁺³ nanoparticles in a core/shell structure to ensure successive energy transfer between the new UC sensitizer (Nd⁺³) to the upconverting activator (Er⁺³). Finally, we synthesized water-tolerant YVO₄:Er⁺³,Yb⁺³@Nd⁺³ core/shell nanoparticles (average size 20 nm) with strong UC luminescence at a biocompatible excitation wavelength for optical temperature sensing where overheating in water is minimized.

Facile microwave synthesis of ScPO4·2H2O flowerlike superstructures: morphology control, electronic structure and multicolor tunable luminescent properties

ScP0₄·2H₂O flowerlike superstructures constructed by well-aligned nanorods were prepared and multicolor tunable emission including white light emission was realized by adjusting the relative doping concentration.

Demonstration of Temperature Dependent Energy Migration in Dual-Mode YVO4: Ho3+/Yb3+ Nanocrystals for Low Temperature Thermometry

A dual mode rare-earth based vanadate material (YVO₄: Ho³⁺/Yb³⁺), prepared through ethylene glycol assisted hydrothermal method, demonstrating both downconversion and upconversion, along with systematic investigation of the luminescence spectroscopy within 12–300 K is presented herein. The energy transfer processes have been explored via steady-state and time-resolved spectroscopic measurements and explained in terms of rate equation description and temporal evolution below room temperature. The maximum time for energy migration from host to rare earth (Ho³⁺) increases (0.157 μs to 0.514 μs) with the material’s temperature decreasing from 300 K to 12 K. The mechanism responsible for variation of the transients’ character is discussed through thermalization and non-radiative transitions in the system. More significantly, the temperature of the nanocrystals was determined using not only the thermally equilibrated radiative intra-4f transitions of Ho³⁺ but also the decay time and rise time of vanadate and Ho³⁺ energy levels. Our studies show that the material is highly suitable for temperature sensing below room temperature. The maximum relative sensor sensitivity using the rise time of Ho³⁺ energy level (⁵F₄/⁵S₂) is 1.35% K⁻¹, which is the highest among the known sensitivities for luminescence based thermal probes.

Sensing temperature via downshifting emissions of lanthanide-doped metal oxides and salts. A review

Temperature is important because it has an effect on even the tiniest elements of daily life and is involved in a broad spectrum of human activities. That is why it is the most commonly measured physical quantity. Traditional temperature measurements encounter difficulties when used in some emerging technologies and environments, such as nanotechnology and biomedicine. The problem may be alleviated using optical techniques, one of which is luminescence thermometry. This paper reviews the state of luminescence thermometry and presents different temperature read-out schemes with an emphasis on those utilizing the downshifting emission of lanthanide-doped metal oxides and salts. The read-out schemes for temperature include those based on measurements of spectral characteristics of luminescence (band positions and shapes, emission intensity and ratio of emission intensities), and those based on measurements of the temporal behavior of luminescence (lifetimes and rise times). This review (with 140 references) gives the basics of the fundamental principles and theory that underlie the methods presented, and describes the methodology for the estimation of their performance. The major part of the text is devoted to those lanthanide-doped metal oxides and salts that are used as temperature probes, and to the comparison of their performance and characteristics.

Deformation Behavior across the Zircon-Scheelite Phase Transition

The pressure effects on plastic deformation and phase transformation mechanisms of materials are of great importance to both Earth science and technological applications. Zircon-type materials are abundant in both nature and the industrial field; however, there is still no in situ study of their deformation behavior. Here, by employing radial x-ray diffraction in a diamond anvil cell, we investigate the dislocation-induced texture evolution of zircon-type gadolinium vanadate (GdVO_{4}) in situ under pressure and across its phase transitions to its high-pressure polymorphs. Zircon-type GdVO_{4} develops a (001) compression texture associated with dominant slip along ⟨100⟩{001} starting from 5 GPa. This (001) texture transforms into a (110) texture during the zircon-scheelite phase transition. Our observation demonstrates a martensitic mechanism for the zircon-scheelite transformation. This work will help us understand the local deformation history in the upper mantle and transition zone and provides fundamental guidance on material design and processing for zircon-type materials.

Pulsed Laser Deposited Dysprosium-Doped Gadolinium-Vanadate Thin Films for Noncontact, Self-Referencing Luminescence Thermometry

Lanthanide-doped vanadate thin films offer (i) a promising platform for luminescence-based noncontact temperature sensing; (ii) ratiometric/self-referencing absolute measurements; (iii) exceptional repeatability and reversibility for multirun uses and a long life cycle; (iv) 2% K(-1) maximum temperature sensitivity (among the highest recorded for inorganic nanothermometers); (v) a temperature resolution greater than 0.5 K; and (vi) the potential for high-resolution 2D temperature mapping.

Structural evaluations and temperature dependent photoluminescence characterizations of Eu(3+)-activated SrZrO3 hollow spheres for luminescence thermometry applications

This research is focused on the temperature sensing ability of perovskite SrZrO3:Eu(3+) hollow spheres synthesized via the sol-gel method followed by heating. The Rietveld refinement indicated that the precursors annealed at 1100 °C were crystallized to form orthorhombic SrZrO3. SrZrO3 particles exhibited non-agglomerated hollow spherical morphology with an average particle size of 300 nm. The UV-excited photoluminescence spectrum of SrZrO3:Eu(3+) consisted of two regions. One region was associated with SrZrO3 trap emission, and the other one was related to the emission of Eu(3+) ions. The intensity ratio of the emission of Eu(3+) ions to the host emission (FIR) and the emission lifetime of Eu(3+) ions were measured in the temperature range of 300-550 K. The sensitivity obtained via the lifetime method was 7.3× lower than that measured via the FIR. Within the optimum temperature range of 300-460 K, the as-estimated sensor sensitivity was increased from 0.0013 to 0.028 K(-1). With a further increase in temperatures, the sensitivity started to decline. A maximum relative sensitivity was estimated to be 2.22%K(-1) at 460 K. The resolutions in both methods were below 1K in the above temperature range. The results indicated the suitability of SrZrO3:Eu(3+) for the distinct high temperature sensing applications.

Luminescence and luminescence quenching of highly efficient Y2Mo4O15:Eu(3+) phosphors and ceramics

A good LED phosphor must possess strong enough absorption, high quantum yields, colour purity, and quenching temperatures. Our synthesized Y₂Mo₄O₁₅:Eu³⁺ phosphors possess all of these properties. Excitation of these materials with near-UV or blue radiation yields bright red emission and the colour coordinates are relatively stable upon temperature increase. Furthermore, samples doped with 50% Eu³⁺ showed quantum yields up to 85%, what is suitable for commercial application. Temperature dependent emission spectra revealed that heavily Eu³⁺ doped phosphors possess stable emission up to 400 K and lose half of the efficiency only at 515 K. In addition, ceramic disks of Y₂Mo₄O₁₅:75%Eu³⁺ phosphor with thickness of 0.71 and 0.98 mm were prepared and it turned out that they efficiently convert radiation of 375 and 400 nm LEDs to the red light, whereas combination with 455 nm LED yields purple colour.

Thermal Scanning at the Cellular Level by an Optically Trapped Upconverting Fluorescent Particle

3D optical manipulation of a thermal-sensing upconverting particle allows for the determination of the extension of the thermal gradient created in the surroundings of a plasmonic-mediated photothermal-treated HeLa cancer cell.

Functional up-converting SrTiO3:Er(3+)/Yb(3+) nanoparticles: structural features, particle size, colour tuning and in vitro RBC cytotoxicity

SrTiO3 nanoparticles co-doped with a broad concentration range of Er(3+) and Yb(3+) ions were fabricated using the citric route as a function of annealing temperatures of 500-1000 °C. The effect of a broad co-dopant concentration range and sintering temperature on structural and up-conversion properties was investigated in detail by X-ray diffraction techniques and optical spectroscopy. The TEM technique was used to estimate the mean particle size, which was around 30 nm for the inorganic product annealed at 600 °C. Up-conversion emission color tuning was achieved by particle size control. Power dependence of the green and red emissions was found to be a result of temperature determination in the operating range of SrTiO3 nanoparticles and a candidate for the fast and local microscopic heating and heat release induced by IR irradiation. The color changed from white-red-yellow-green upon an increase of sintering temperature, inducing changes in the surface-to-volume ratio and the number of optically active ions in particle surface regions. The cytotoxic activity of nanoparticles on human red blood cells was investigated, showing no harmful effects up to a particle concentration of 0.1 mg ml(-1). The cytotoxic response of a colloidal suspension of nanoparticles to RBC cells was connected with the strong affinity of SrTiO3 particles to the cell membranes, blocking the transport of important biological solutes.

Structure and photoluminescent properties of green-emitting terbium-doped GdV1-x Px O4 phosphor prepared by solution combustion method

Terbium-doped gadolinium orthovanadate (GdVO4 :Tb(3+) ), orthophosphate monohydrate (GdPO4 ·H2 O:Tb(3+) ) and orthovanadate-phosphate (GdV,PO4 :Tb(3+) ) powder phosphors were synthesized using a solution combustion method. X-Ray diffraction analysis confirmed the formation of crystalline GdVO4 , GdPO4 ·H2 O and GdV,PO4 . Scanning electron microscopy images showed that the powder was composed of an agglomeration of particles of different shapes, ranging from spherical to oval to wire-like structures. The chemical elements present were confirmed by energy dispersive spectroscopy, and the stretching mode frequencies were determined by Fourier transform infrared spectroscopy. UV-visible spectroscopy spectra showed a strong absorption band with a maximum at 200 nm assigned to the absorption of VO4 (3-) and minor excitation bands assigned to f → f transitions of Tb(3+) . Four characteristic emission peaks were observed at 491, 546, 588 and 623 nm, and are attributed to (5) D4  → (7) Fj (j = 6, 5, 4 and 3). The photoluminescent prominent green emission peak ((5) D4  → (7) F5 ) was centred at 546 nm. The structure and possible mechanism of light emission from GdV1-x Px O4 :% Tb(3+) are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Optical temperature sensing in β-NaLuF4:Yb3+/Er3+/Tm3+ based on thermal, quasi-thermal and non-thermal coupling levels

Three methods for optical temperature sensing are investigated in the NaLuF₄:Yb³⁺/Er³⁺/Tm³⁺ phosphor, based on thermal, quasi-thermal and non-thermal coupling levels.

Enhanced temperature sensing response of upconversion luminescence in ZnO-CaTiO3: Er(3+)/Yb(3+) nano-composite phosphor

Upconversion emission and temperature sensing of the Er(3+)/Yb(3+) doped ZnO-CaTiO3 nano-composite phosphor is studied by varying the ZnO concentration. The XRD and EDX studies reveal the formation of composite phase when ZnO doping exceeds above 10 mw%. Five prominent upconversion emission bands at 410, 492, 524, 545 and 662 nm corresponding to (2)H9/2→(4)I15/2, (4)F3/2→(4)I15/2, (2)H11/2→(4)I15/2, (4)S3/2→(4)I15/2 and (4)F9/2→(4)I15/2 transitions, respectively are found under 980 nm excitation from a diode laser. On the basis of rise time analysis it was found that energy transfer process is responsible for the intense upconversion emission. Large reduction in decay time of (4)S3/2 level is observed on the ZnO incorporation in host matrix. Moreover, the absolute sensor sensitivity, relative sensor sensitivity and calculated color coordinates of the samples are also determined. These results indicate the potentiality of this composite phosphor for various applications.