Colloidal chemical nanosensors based on trivalent europium ions luminescence

Hemijski senzori privlaĉe mnogo paţnje zbog raznovrsnih primena u svakodnevnom ţivotu. Jedna od podvrsta senzora su i optiĉki hemijski senzori zasnovani na korišćenju optiĉkih metoda kao što su apsorpcija, rasejavanje svetlosti, fluorescencija, itd. U okviru ove doktorske disertacije istraţivanje je zapoĉeto sintezom serije uzoraka na bazi lantan fosfata (LaPO4) koji su aktivirani jonima europijuma (Eu3+) u širokom opsegu koncentracija (aktiviranje je izvršeno u opsegu 0 ≤ x ≤ 1 za sistem La1-xEuxPO4, gde je x udeo Eu3+ jona). Materijali su sintetisani koloidnom sintezom uz upotrebu citratnih jona za dobijanje kompleksnih jedinjenja retkih zemalja (La3+ (Eu3+)-Cit3- ). Iz serije sintetisanih uzoraka odabrana su dva sistema za dalje eksperimente: La0,5Eu0,5PO4 i jedinjenje u kom su joni La3+ u potpunosti zamenjeni jonima Eu3+ – stehiometrijski EuPO4. Sintetisana su još dva uzorka u kojima su: (a) joni lantana (La3+) zamenjeni jonima disprozijuma (Dy3+) i (b) joni lantana (La3+) zamenjeni jonima erbijuma (Er3+), pri ĉemu je koncentracija europijuma bila x = 0,5 (Dy1-xEuxPO4 i Er1-xEuxPO4). Svi uzorci su monokliniĉne monazitne kristalne strukture sa P121/m1 prostornom grupom. Dobijene su ĉestice nanodimenzija, preteţno sfernog oblika ĉije su optiĉke osobine detaljno ispitane. Sve ispitivane uzorke karakteriše intenzivna emisija u crvenom delu elektromagnetnog spektra na oko 592 nm i 618 nm koja potiĉe od jona europijuma. Mogućnost sintetisanih uzoraka da se u koloidnoj formi ponašaju kao hemijski nanosenzori zasniva se na praćenju promena intenziteta luminescencije jona europijuma. Do smanjenja intenziteta luminescencije dolazi u prisustvu razliĉitih supstanci koje se ponašaju kao gasitelji intenziteta luminescencije – kvenĉeri (engl. Quencher). Lista analita za hemijski senzing je opseţna i obuhvata katjone, anjone, toksiĉne gasove, pesticide, isparenja, produkte aktivnosti enzima kao sto je H2O2, itd. U okviru ove disertacije ispitivana je osetljivost sintetisanih uzoraka na prisustvo metala (Cu2+, Hg2+, Cd2+, Pb2+, Zn2+) i pesticida (2,4- dihlorfenoksisirćetna kiselina (2,4-D) i 2-metil-4-hlorfenoksisirćetna kiselina (MCPA)). Navedeni kvenĉeri luminescencije, korišćeni u okviru disertacije, predstavljaju ĉeste zagaĊivaĉe ţivotne sredine koji mogu imati neposredan uticaj na ljudsko zdravlje. Upotreba fluorescencije kao metode za detekciju koja je u odnosu na postojeće metode u upotrebi, jednostavnija, brţa i manje zahtevna kako prilikom snimanja uzoraka, tako i prilikom pripreme uzorka, predstavlja veliku prednost. Osim fotoluminescentnih (emisioni i eksitacioni spektri, odreĊivanje vremena ţivota) i UV -VIS (engl. Ultra violet-visible) merenja za svaki sistem u prisustvu razliĉitih gasitelja emisije odreĊene su konstante kvenĉovanja na osnovu Stern-Volmer jednaĉine kao i limiti detekcije. Najveća osetljivost sintetisanih sistema kao i najniţi limit detekcije dobijen je kada su kao kvenĉer intenziteta emisije Eu3+ korišćeni joni Cu2+ . Intenzitet emisije jona Eu3+ koji opada dodatkom kvenĉera (eksperiment sa jonima Cu2+) ponovo je uspostavljen dodatkom vodenog rastvora EDTA (kompleksirajuće sredstvo). Znaĉaj ovog eksperimenta je u ĉinjenici da ukazuje na mogućnost ponovne upotrebe nanosenzora. Rezultati dobijeni u okviru ove disertacije otvaraju mogućnost za razvoj novih sistema koji bi se potencijalno koristili kao hemijski senzori u mnogobrojnim oblastima kao što su kontrola kvaliteta hrane, aerodinimika, biohemija ili zaštita ţivotne sredine.Chemical sensors attract a lot of attention due to a variety of applications in everyday life. One of the sensor subtypes are optical chemical sensors which are based on the usage of optical methods such as absorption, light scattering, fluorescence, etc. The investigations throughout this doctoral dissertation started with the synthesis of a series of samples based on LaPO4 systems that have been activated with europium ions (Eu3+ ) in wide concentration range (activation is performed in the range 0 ≤ x ≤ 1 for the La1- xEuxPO4 system, where x is the fraction of Eu3+ ions). Materials were obtained by colloidal synthesis using citrate ions for the production of complex rare earth compounds (La3+ (Eu3+ )-Cit3- ). From the series of synthesized samples, two samples were selected for further experiments: La0.5Eu0.5PO4 and the one in which the La3+ ions are completely replaced by the Eu3+ ions – stoichiometric EuPO4. Two more samples were synthesized: (a) one where the lanthanum ions (La3+) were replaced by dysprosium ions (Dy3+), and (b) one where the lanthanum ions (La3+) was replaced by erbium ions (Er3+); the concentration of europium ions was x = 0.5 (Dy1-xEuxPO4 and Er1-xEuxPO4). All samples have pure monoclinic monazite crystal structure with P121/n1 space group. Ultrasmall round shaped nanoparticles were obtained and their optical properties were thoroughly examined. All the tested samples are characterized by the dominant red luminescence in the electromagnetic spectrum with two intense emission lines: at about 592 nm and 618 nm, originating from the europium ions. The ability of synthesized materials to act as chemical nanosensors in the colloidal form is based on monitoring the changes in the intensity of luminescence of the europium ions. A decrease in the intensity of luminescence occurs in the presence of various ranges of substances that act as quenchers. The list of analytes for chemical sensing is very extensive and it includes cations, anions, toxic gases, vapors, products of the enzymatic action such as H2O2, etc. Within this dissertation, the sensitivity of the synthesized systems to the presence of heavy metal ions (Cu2+, Hg2+, Cd2+, Pb2+ , Zn2+) and pesticides (2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4- chlorophenoxyacetic acid (MCPA)) was investigated. Quenchers of luminescence mentioned above represent common environmental pollutants that may have an indirect impact on human health. The usage of a method such as fluorescence which is compared to existing methods in use simple, less time consuming and demanding when preparing a sample, is a great advantage. In addition to photoluminescent (excitation, emission, lifetime) and UV-VIS measurements quenching constants based on the Stern-Volmer equation were determined for each system in the presence of various quenchers, as well as the limit of detections. The highest sensitivity of synthesized systems to presence of quenchers and the lowest detection limit was obtained for Cu2+ ions. The emission intensity of the Eu3+ ions which decreases with the addition of the quencher (an experiment with Cu2+ ions as quencher) was recovered by the addition of an aqueous EDTA solution (complexing agent). The experiment with the recovery of the initial intensity of the emission is important because it points to the possibility of the fluorescent probe reusabillity. The results obtained in this dissertation open up the possibility of developing new systems that could potentially be used as chemical sensors in many areas such as food quality control, aerodynamics, biochemistry or environmental protection

Particle size effects on the structure and emission of Eu3+:LaPO4 and EuPO4 phosphors

The authors acknowledge the financial support of the Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056). T.G acknowledges to the ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001).This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100 nm), 4 × 20 nm nanorods and 5 nm spheres (depending on the annealing temperature), 2 × 15 nm nanorods, and ultra-small spheres (2 nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2 Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592 nm (5D0→7F1), at 612 nm (5D0→7F2), at 652 nm (5D0→7F3) and at 684 nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.Ministry of Education, Science and Technological Development of the Republic of Serbia (Projects nos. 45020 and 172056); ERDF PostDoc project No. 1.1.1.2/VIAA/1/16/215 (1.1.1.2/16/I/001); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART

MgAl2O4:Cr3+ probe for luminescence thermometry in the physiological temperatures range

Temperature sensing from the photoluminescence of MgAl2O4:Cr3+ powder is systematically examined and presented. The material was prepared by the self-propagating high-temperature synthesis method and its structure was confirmed by X-ray diffraction analysis. In this host, Cr3+ ions are in a strong crystal field, so the overlapping emissions from 2E and 4T2 energy levels are observed. Emission and excitation spectra were recorded in the 300 - 540 K temperature range. The broad photoluminescence attributed to 4T2→4A2 transition increases in intensity with an increase in temperature on account of 2E→4A2 emission intensity until 460 K when both emissions start quenching. The emissions were separated by deconvolution at each temperature and used for the luminescence intensity ratio temperature readout method. The obtained relative sensitivity displayed high values in the physiological range, from 3.5 %K-1 at 300 K to 2.9 %K-1 at 330 K, above 2 %K-1 below 400 K, and above 1 %K-1 between 400 K and 540 K.ICOM&IWPPP 2022 : August 29 - September 2, 2022, Belgrad

Using Principal Component Analysis for Temperature Readings from YF3:Pr3+ Luminescence

The method of measuring temperature using luminescence by analyzing the emission spectra of Pr3+-doped YF3 using principal component analysis is presented. The Pr3+-doped YF3 is synthesized using a solid-state technique, and its single-phase orthorhombic crystal structure is confirmed using X-ray diffraction. The emission spectra measured within the 93–473 K temperature range displays characteristic Pr3+ f-f electronic transitions. The red emission from the 3P0,1→3H6,3F2 electronic transition mostly dominates the spectra. However, at low temperatures, the intensity of the green emissions from the 3P0,1→3H5, deep-red 3P0,1→3F4, and the deep-red emissions from the 3P0,1→3F4 transitions are considerably lower compared to the intensity of the red emissions. Temperature variations directly impact the photoluminescent spectra, causing a notable increase in the green and deep-red emissions from the 3P1 excited state. We utilized the entire spectrum as an input for principal component analysis, considering each temperature as an independent group of data. The first principal component explained 99.3% of the variance in emission spectra caused by temperature and we further used it as a reliable temperature indicator for luminescence thermometry. The approach has a maximum absolute sensitivity of around 0.012 K−1. The average accuracy and precision values are 0.7 K and 0.5 K, respectively

In-band luminescence thermometry in the third biological window and multicolor emission of Er-doped fluoride and oxide nanoparticles

In this study we present a morphological and spectroscopical characterization of three different erbium doped nanocrystal samples, namely two oxides (Y2O3:3%Er, Sc2O3:3%Er) and one fluoride (YF3:5%Er). The spectroscopic study offers a comprehensive comparison of their multicolor emissions, ranging from the visible to the mid-infrared region. Emissions from the first five excited states are presented and the emission cross sections of the 4I11/2 → 4I15/2, 4I11/2 → 4I13/2, and 4I13/2 → 4I15/2 transitions have been calculated and compared with literature results for the oxide compounds providing a confirmation for the 1.5 emission of Er:Y2O3, a correction over published values for the 2.7 μm emission of Er:Y2O3, and also new results for the Er:Sc2O3 emission cross section values of all the infrared bands. Moreover, this study explores the application of the 4I13/2 emission for in-band luminescence thermometry within the third biological window. An optimized segmentation of the 1.5 μm emission permits to achieve high relative and absolute sensitivities using just one dopant ion

Twofold increase in the sensitivity of Er3+/Yb3+ Boltzmann thermometer

Luminescence thermometry is the most versatile remote temperature sensing technique and can be employed from living cells to large surfaces and from cryogenic temperatures to the melting points of metals. Ongoing research aims to optimize the sensitivity of the ratio between the emission intensity from two coupled excited states. However, this approach is inherently limited to temperature-dependent processes involving only the excited states. Here, we develop a novel measurement technique, called luminescence intensity ratio squared (LIR2) for the Yb3+/Er3+ pair, that combines the temperature sensitivity of ground- and excited-state populations. We use Y3Al5O12:Er3+,Yb3+ nanoparticles as a promising model system with both visible and infrared emissions. To apply our method, we record two luminescence spectra at different excitation wavelengths and determine the LIR2 using one emission in each of the two spectra. The LIR2 testing with Y3Al5O12 nanoparticles showed a sensitivity increase of 70% in the visible region and an impressive 230% increase in the NIR region compared to the conventional LIR method. This enhances the measurement precision by a factor of 1.5-2.5. The LIR2 based on the visible upconversion emission is particularly useful for measurements of high temperatures, while the LIR2 based on the downshifted ∼1.5 μm emission may revolutionize temperature measurements of biological samples in the range of physiological temperatures

All near-infrared multiparametric luminescence thermometry using Er3+, Yb3+-doped YAG nanoparticles

This paper presents four new temperature readout approaches to luminescence nanothermometry in spectral regions of biological transparency demonstrated on Yb3+/Er3+-doped yttrium aluminum garnet nanoparticles. Under the 10 638 cm-1 excitation, down-shifting near infrared emissions (>10 000 cm-1) are identified as those originating from Yb3+ ions' 2F5/2 → 2F7/2 (∼9709 cm-1) and Er3+ ions' 4I13/2 → 4I15/2 (∼6494 cm-1) electronic transitions and used for 4 conceptually different luminescence thermometry approaches. Observed variations in luminescence parameters with temperature offered an exceptional base for studying multiparametric temperature readouts. These include the temperature-dependence of: (i) intensity ratio between emissions from Stark components of Er3+ 4I13/2 level; (ii) intensity ratio between emissions of Yb3+ (2F5/2 → 2F7/2 transition) and Er3+ (4I13/2 → 4I15/2 transition); (iii) band shift and bandwidth and (iv) lifetime of the Yb3+ emission (2F5/2 → 2F7/2 transition) with maximal sensitivities of 1% K-1, 0.8% K-1, 0.09 cm-1 K-1, 0.46% K-1 and 0.86% K-1, respectively. The multimodal temperature readout provided by this material enables its application in different luminescence thermometry setups as well as improved the reliability of the temperature sensing by the cross-validation between measurements. © 2021 The Royal Society of Chemistry

Exploiting High-Energy Emissions of YAlO3:Dy3+ for Sensitivity Improvement of Ratiometric Luminescence Thermometry

The sensitivity of luminescence thermometry is enhanced at high temperatures when using a three-level luminescence intensity ratio approach with Dy3+- activated yttrium aluminum perovskite. This material was synthesized via the Pechini method, and the structure was verified using X-ray diffraction analysis. The average crystallite size was calculated to be around 46 nm. The morphology was examined using scanning electron microscopy, which showed agglomerates composed of densely packed, elongated spherical particles, the majority of which were 80–100 nm in size. The temperature-dependent photoluminescence emission spectra (ex = 353 nm, 300–850 K) included Dy3+ emissions in blue (458 nm), blue (483 nm), and violet (430 nm, T 600 K). Luminescence intensity ratio, the most utilized temperature readout method in luminescent thermometry, was used as the testing method: a) using the intensity ratio of Dy3+ ions and 4I15/2→6H15/2/4F9/2→6H15/2 transitions; and b) employing the third, higher energy 4G11/2 thermalized level, i.e., using the intensity ratio of 4G11/2→6H15/2/4F9/2→6H15/2 transitions, thereby showing the relative sensitivities of 0.41% K−1 and 0.86% K−1 at 600 K, respectively. This more than doubles the increase in sensitivity and therefore demonstrates the method’s usability at high temperatures, although the major limitation of the method is the chemical stability of the host material and the temperature at which the temperature quenching commences. Lastly, it must be noted that at 850 K, the emission intensities from the energetically higher levels were still increasing in YAP: Dy3+

Novel Y3NbO7:xDy3+ phosphor and its tunable emission

As yttrium niobates, the Y2O3–Nb2O5 combination exists in two forms: YNbO4 and Y3NbO7, and the latter has been studied as a host for photoluminescent ions to a limited extent [1-3]. In this research, the powders of Y3NbO7:xDy3+ (x = 0.5, 1, 1.5, 3 and 5 mol%) were produced through a solid-state process. X-ray diffraction investigations confirmed the fluorite-type structure (space group ) of powders with crystallite size in the range of 19–60 nm. Both the photoluminescence excitation and emission spectra revealed the presence of defects within the material. With different excitation wavelengths, the emission spectra exhibited distinct emission patterns. At each excitation wavelength, the emission was quenched at Dy3+ concentration higher than 1mol%. The decay time measurements of the highest intensity emission revealed a progressive decrease from 0.472 milliseconds for x = 0.5 mol% to 0.246 milliseconds for x = 5 mol%. The CIE chromaticity coordinates investigation revealed that the emission color may be altered by varying the excitation wavelength, ranging from blue (excitation at 333 nm) and nearwhite (excitation at 353 nm and 390 nm) to orange (excitation at 457 nm). The chromaticity of emission under 353 nm and 390 nm excitation validated the material's suitability as an almostwhite phosphor.SCOM 2023 : 18th - 20st of October 2023, Belgrade