Aleksandar Ćirić

• Doctor of Philosophy
• Research Assistant at Vinča Institute of Nuclear Sciences

Sr2LaF7:xPr3+ (x = 0.2, 1, 2, 3, 5, 10, and 25 mol%) nanophosphors with a cubic Fm3m structure were hydrothermally synthesized, forming nearly spherical nanoparticles with an average diameter of approximately 32 nm. Diffuse reflectance measurement and excitation spectra showed a primary excitation peak of Pr3+ at 443 nm, corresponding to the ground...

Over the past three decades, luminescence thermometry has gained significant attention among researchers and practitioners. The method has progressed in terms of utilizing temperature-sensitive luminescent materials, obtaining temperature read-outs from luminescence, developing applications, and improving performance. This paper reviews and critica...

Accurate temperature measurement is critical across various scientific and industrial applications, necessitating advancements in thermometry techniques. This study explores luminescence thermometry, specifically utilizing machine learning methodologies to enhance temperature sensitivity and accuracy. We investigate the performance of principal com...

Herein, we report the photoluminescence properties of Bi³⁺-sensitized BaYF5:10 mol%Eu³⁺ nanoparticles. The emission spectra feature Eu³⁺ peaks corresponding to transitions from the ⁵D0 excited to ⁷FJ (J = 1, 2, 3, 4) lower levels with two dominant emissions positioned in the orange-red (∼ 592 nm, ⁵D0 → ⁷F1) and deep-red (∼ 697 nm, ⁵D0 → ⁷F4) region...

Detailed analysis covered the optical and structural properties of Eu³⁺-doped NaY9Si6O26 oxyapatite phosphors, which were obtained via hydrothermal synthesis. X-ray diffraction patterns of NaY9Si6O26:xEu³⁺ (x = 0, 1, 5, 7, 10 mol% Eu³⁺) samples proved a single-phase hexagonal structure (P63/m (176) space group). Differential thermal analysis showed...

Tunable blue/red dual-emitting Eu³⁺-doped, Bi³⁺-sensitized SrF2 phosphors were synthesized utilizing a solvothermal-microwave method. All phosphors have cubic structure (Fm-3m (225) space group) and well-distinct sphere-like particles with a size of ~20 nm, as examined by X-ray diffraction and transmission electron microscopy. The diffuse reflectan...

Luminescent thermometers are highly effective in niche applications such as nanothermometry, in vivo imaging, and extreme conditions like high electromagnetic fields, radiation, and under mechanical or chemical stress. Advancing measurement precision, temperature resolution, and extending the temperature range are the main problems in this rapidly...

A set of Eu³⁺-doped molybdates, Y2−xEuxMo3O12 (x = 0.04; 0.16; 0.2; 0.4; 0.8; 1; 1.6; 2), was synthesized using a solid-state technique and their properties studied as a function of Eu³⁺ concentration. X-ray diffraction showed that the replacement of Y³⁺ with larger Eu³⁺ resulted in a transformation from orthorhombic (low doping concentrations) thr...

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 confirm the fluorite-type structure (space group 𝐹𝑚3̅𝑚) 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 th...

Luminescence thermometry is a remote temperature sensing method by observing temperature dependent spectral changes for temperature readout. Chase for increasing temperature readout sensitivity motivated research of employing 3rd thermalized level of Er3+ emission in Yb3+/Er3+ upconversion photoluminescence. For this purpose, highly stable and effi...

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been...

Orthorhombic Ta2O5:Er3+ coatings were obtained by plasma electrolytic oxidation (PEO) of tantalum in an alkaline electrolyte with the addition of Er2O3 particles in various concentrations. Down-conversion photoluminescence (PL) emission spectra is featured by sharp bands attributed to 4f–4f transitions of Er3+. The most intense green PL emission ba...

Upconversion nanoparticles show an increasing interest that is not bound to stop for many years to come. The upconversion is observed in various materials, from transition metals, semiconductor quantum dots, lanthanide ions, organic nanoparticles, and their combinations. The advancement in the field and increase in luminescence efficiency is closel...

This study demonstrated that Ta2O5 coatings formed by plasma electrolytic oxidation of tantalum substrate in an alkaline electrolyte containing Ho2O3 nanoparticles have the potential to be used as a host for Ho³⁺ ions. Down-conversion photoluminescence (PL) intensity of Ta2O5:Ho³⁺ is strongly dependent on the concentration of Ho³⁺ incorporated into...

The industrial applications of luminescent coatings for temperature sensing and high‐security QR codes have multiple inherent problems in their application (speed, cost, industrial feasibility) or properties (poor adhesion, chemical, thermal stability, or thermal contact). Luminescent coatings created by the electrochemical Plasma Electrolytic Oxid...

The sensitivity of luminescent Boltzmann thermometers is restricted by the energy difference between the thermally coupled excitement levels of trivalent lanthanides, and their values further decrease with increases in temperature, rendering their use at high temperatures difficult. Here, we demonstrate how to overcome this sensitivity limitation b...

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 appr...

Luminescence with temperature changes in its intensity, energy, spectral shape, peak width in the steady-state, or lifetime and phase shift in the impulse regime. Those most often undesired effects (but endorsed for the luminescence thermometry) have been modeled depending on the material type and physical phenomena involved, resulting in numerous...

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 calculat...

Down‐conversion photoluminescent ZrO 2 : Ln 3+ (Ln = Eu, Sm, Er, Tb, Ho, Tm, Pr, Gd, Dy) films were prepared by the plasma electrolytic oxidation (PEO) method from a pure zirconium foil, by adding Ln 2 O 3 particles to a basic electrolyte. Photoluminescence (PL) emission spectra of ZrO 2 : Ln 3+ films are characterized by a broad band of ZrO 2 host...

Y3NbO7:xEu3+ powders (x = 0.25, 0.5, 0.75, 2, 3, 5, 10 at%) were synthesized by a two-step vibrational milling, alternating with annealing. All the samples crystallize as fluorite-type structure, with crystallite size 50–60 nm and show a strong orange/red luminescence with an excited state lifetime around 1.2 ms. Photoluminescence excitation and em...

A series of LaGa1–xO3:Cr³⁺x phosphors (x = 0.002, 0.005, 0.01, 0.02, 0.04) were synthesised by solid-state reaction and structurally characterised by Rietveld refinement from powder X-ray diffraction data. Amongst the five compounds, that with x = 0.01 exhibited the highest photoluminescence quantum yield at room temperature, those with higher dopi...

Temperature-induced bandshift of luminescence peaks is frequently described with McCumber-Sturge relation which is difficult for fitting or practical applications due to its mathematical complexity. Here for the first time, we give its exact solution in terms of polylogarithms, and an excellent approximation that is better at lower temperatures tha...

In response to the sensitivity limitation of ratiometric luminescence thermometers, herein we propose a novel temperature readout, which exploits two pairs of thermalized energy levels in trivalent lanthanide ion-activated phosphors, to provide significantly enhanced sensitivity. This method is called the luminescence intensity ratio squared (LIR ²...

Eu3+-doped YxLu1−xNbO4 (x = 0, 0.25, 0.5, 0.75, 1) were prepared by the solid-state reaction method. YNbO4:Eu3+ and LuNbO4:Eu3+ crystallize as beta-Fergusonite (SG no. 15) in 1–10 μm diameter particles. Photoluminescence emission spectra show a slight linear variation of emission energies and intensities with the solid-solution composition in terms...

Energy level positions, refractive index values, Judd–Ofelt (JO) intensity parameters, Slater integrals, and spin‐orbit coupling parameters are taken from the literature for 27 Dy³⁺‐doped materials (five crystals and 22 glasses). Investigated are only the transitions that are used for the Boltzmann‐type luminescence intensity ratio (LIR) thermomete...

We report on overcoming the sensitivity limit of Boltzmann's thermometers by utilization of seven thermalized Dy³⁺ excited states in the Lu1.5Y1·5Al5O12 host. Emission spectra recorded from room temperature to 938 K show transitions originating from seven ⁴F9/2, ⁴I15/2, ⁴G11/2, ⁴I13/2, ⁴M21/2, ⁴K17/2, and ⁴F7/2 excited levels to the ⁶H15/2 ground s...

Judd–Ofelt theory is a cornerstone of lanthanides’ spectroscopy given that it describes 4fn emissions and absorptions of lanthanide ions using only three intensity parameters. A self-referenced technique for computing Judd–Ofelt intensity parameters from the excitation spectra of Eu3+-activated luminescent materials is presented in this study along...

Phosphors for luminescence thermometry La 1− x Ga 0.99 O 3 :Cr 0.01 , Nd x were synthesised by the solid-state method, structurally characterised using powder X-ray diffraction data, and investigated by ambient and variable-temperature optical measurements.

15 μm thick Ti-Sapphire coatings were synthesized at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominan...

The highly-efficient upconversion photoluminescent ZrO2:Ln³⁺/Yb³⁺ (Ln = Er, Ho, Tm) films were prepared by the plasma electrolytic oxidation method from the pure zirconium foil, by adding Ln2O3 and Yb2O3 particles to the supporting electrolyte, in various concentrations. The method of synthesis, morphology, chemical, and phase composition of formed...

Upconversion sub-micron particles are one of the most perspective materials due to their wide application range, the most important being in the bio-medicinal field where they can be used for labeling, sensing, treatment or drug delivery. Chemically stable upconversion sub-micron particles of La2O2S co-doped with Yb³⁺/Ho³⁺ and Yb³⁺/Tm³⁺ were synthe...

Two experimental practices in luminescence intensity ratio (LIR) thermometry based on the spectral deconvolution (SD) and separation at chosen wavelength (WS) were analyzed for the case when sharp emission is overlapping with a broad one, which is frequently the case for Cr³⁺ and Mn⁴⁺ in the intermediate or strong crystal fields. Their performances...

Judd-Ofelt theory presents a centrepiece in spectroscopy of lanthanides since it explains and predicts 4f absorptions and emissions from only 3 intensity parameters. A self-referenced method for calculating Judd–Ofelt intensity parameters from the excitation spectra of Eu3+-activated luminescent materials is proposed in this study along with a desc...

Mn2+ single doped as well as Mn2+/Eu2+ and Mn2+/Ce3+ co-doped Al2O3 coatings were synthesized by plasma electrolytic oxidation process of aluminum and their structural, morphological, and above all, photoluminescence (PL) properties were investigated in deep. Al2O3:Mn2+ coatings exhibit a weak green PL emission centered at about 525 nm attributed t...

The luminescence thermometry based on the intensity ratio of Cr³⁺ and host emissions in the Cr³⁺ activated MgTiO3 phosphor powder is demonstrated over the 100–350 K temperature range. Phosphor was prepared by a two-step procedure based on the sol-gel and molten salt methods. Rhombohedral crystal structure of the material is confirmed by X-ray diffr...

Thermographic properties of Cr³⁺-doped Al2O3 coatings created by plasma electrolytic oxidation (PEO) are investigated. Scanning electron microscopy revealed dense coatings uniformly distributed over the aluminum surface with uniform elemental maps, confirming homogeneous distribution of chromium ions. X-ray diffraction analysis shows that created c...

Multifunctional coatings of Al2O3 co-doped Tb³⁺ or Tb³⁺/Eu²⁺ were synthesized by the rapid and facile plasma electrolytic oxidation method on pure aluminium substrate. SEM & EDS analysis revealed porous structure independent on the doping concentration, with uniform distribution of co-doped rare-earth elements and incorporated concentrations propor...

Nanoparticles of less than 100 nm of La2O2S co-doped with Er³⁺ and Yb³⁺ in 2% and 12% concentrations, respectively, were synthesized by the improved furnace combustion technique that limits the precursor usage and without the hazardous chemicals. The lanthanum oxysulfide was identified in hexagonal crystal phase. Under 980 nm excitation the sample...

Temperature sensing from the photoluminescence of MgAl2O4:Cr³⁺ ceramic powder is systematically investigated. Material was prepared by self-propagating high temperature synthesis method. In this host, Cr³⁺ experiences the strong crystal field, so the overlapping emissions from ²E and ⁴T2 energy levels are observed. Emission and excitation spectra w...

Judd–Ofelt (JO) theory explains the optical properties of trivalent lanthanides using only three intensity parameters. The JO parametrization is a complicated procedure of absorption spectra analysis, especially cumbersome for powders and non‐transparent materials. For the Pr³⁺ activated materials, the procedure is additionally complicated due to s...

The COVID-19 infectious disease in 2020 caused a global and subsequent lockdown policies imposed by various governments. Public libraries were affected as well. For many public libraries, the only one that remained active and available to users was access to their digital content. The Njegoš public library in Knjaževac, Serbia, responded by improvi...

Eu³⁺ and Tb³⁺ doped ZnO optical coatings were formed by the Plasma Electrolytic Oxidation (PEO) method from the pure Zn sheet, with various dopant concentrations. The morphologies show no significant change with the introduced dopant or their concentrations, with typical appearance of PEO formed coatings. All elements are uniformly distributed, and...

The introduction of additional functionalities to materials is exceptionally important as it opens new applications for them. Aluminum, one of the most abundant and important materials, is coated with luminescent Sm²⁺‐doped γ‐aluminium oxide to impart thermometric functionality. Considering the potential industrial applications, two of the most wid...

This paper is devoted to the study of the photoluminescent (PL) characteristics of blue-emitting Al2O3:Tm3+ and Al2O3:Tm3+/Ce3+ coatings. The presented coatings were synthesized by plasma electrolytic oxidation process of aluminum in electrolyte containing Tm2O3 and Tm2O3/CeO2 particles, and characterized by SEM/EDS, XRD, and PL emission and excita...

The figures of merit of luminescence intensity ratio (LIR) thermometry for Er3+ in 40 different crystals and glasses have been calculated and compared. For calculations, the relevant data has been collected from the literature while the missing data were derived from available absorption and emission spectra. The calculated parameters include Judd–...

The figures of merit of luminescence intensity ratio (LIR) thermometry for Er3+ in 40 different crystals and glasses have been calculated and compared. For calculations, the relevant data has been collected from the literature while the missing data were derived from available absorption and emission spectra. The calculated parameters include Judd-...

A series of new red phosphors based on apatite-type gadolinium silicate host, Gd 9.33−x Eu x (SiO 4 ) 6 O 2 (0.03 < x < 1.87), have been synthesised and analysed.

Nano-crystallite Lanthanum oxysulfide (La2O2S), a versatile compound with a wide range of applications, has been synthesized by the Solid State, Hydrothermal, and a novel Furnace Combustion technique. The last one limits the precursors, thus minimizing the resource usage, does not require passing of the H2S, CS2, or any of the hazardous gasses duri...

The steady-state luminescence thermometry analysis was performed on thin-films of undoped Gd2O3 and Gd2O3 doped with Ho³⁺, Eu³⁺ and Er³⁺, created by the plasma electrolytic oxidation process. The experimental setup for luminescent measurements closely resembles the practical luminescent fiber-optic thermometer. The visible PL from Gd³⁺ was utilized...

The Judd-Ofelt model, already verified for the luminescence intensity ratio (also called fluorescence intensity ratio, FIR) thermometry from the emission spectra, is modified and tested for the double-excitation (also called ground-state-absorption, GSA) thermometry. The adapted model has been tested on Lu2O3:Eu³⁺, with a 99.9% match of the tempera...

In this paper, photoluminescence (PL) properties of Pr³⁺ single doped and Pr³⁺/Eu²⁺ co-doped Al2O3 coatings formed by plasma electrolytic oxidation of aluminum were investigated. The PL spectra of Al2O3:Pr³⁺ coatings feature bands ascribed to 4f-4f transitions of Pr³⁺. PL excitation spectra contain three broad bands in the violet and blue regions w...

In this paper, Dy³⁺ and Dy³⁺/Ce³⁺ doped Al2O3 coatings were synthesized by plasma electrolytic oxidation process of aluminum. Structural and photoluminescence (PL) properties of obtained coatings as well as energy transfer mechanism from Ce³⁺ to Dy³⁺ were studied. The PL excitation and emission spectra of Al2O3:Dy³⁺ featured weak bands attributed t...

The emission of Er 3+ provides three combinations of emission bands suitable for ratiometric luminescence thermometry. Two combinations utilize ratios of visible emissions (2 H 11/2 → 4 I 15/2 at 523 nm/ 4 S 3/2 → 4 I 15/2 at 542 nm and 4 F 7/2 → 4 I 15/2 at 485 nm/ 4 S 3/2 → 4 I 15/2 at 545 nm), while emissions from the third combination are locat...

Zirconia (ZrO2) coatings, doped with Gd³⁺ and Dy³⁺ in various concentrations, were created by the plasma electrolytic oxidation (PEO) process of zirconium by the addition of Gd2O3 and Dy2O3 particles to the supporting electrolyte, respectively. Their morphological, chemical, phase, and above all, photoluminescent (PL) properties were examined. Morp...

Plasma electrolytic oxidation (PEO) of aluminum in electrolytes containing CeO2 and Eu2O3 powders in various concentrations was used for creating Al2O3 coatings doped with Ce3+ and Eu2+ ions. Phase and chemical composition, surface morphology, photoluminescence (PL) properties and energy transfer from Ce3+ to Eu2+ were investigated. When excited by...

Judd-Ofelt analysis has been performed from the photoluminescence emission spectra of Y2O3:Eu3+ with 3%, 1% and 0.1% doping concentration and YVO4:Eu3+ with 1% doping concentration, in temperature range from 40 °C to 460 °C. For precise calculation, an extended Sellmeier equation that accounts for the doping concentration and temperature dependence...

Gd2O3 and Gd2O3:Ln³⁺ (Ln = Eu, Er, Ho) coatings were formed by the fast and cheap plasma electrolytic oxidation (PEO) process, from the pure gadolinium plate and an addition of appropriate Ln2O3 particles to the supporting electrolyte. Monoclinic phase of Gd2O3 is identified in all samples. Gd2O3 absorbs in the UV region and the photoluminescence i...

The red phosphor Y2Mo4O15: Eu3+ calcined at different temperatures is obtained by a solid‐state method, and is investigated in this paper. Usage of solid state method with combination of five different calcined temperatures (500, 550, 600, 650 and 700 °C) led to the formation of pure monoclinic phase in all samples apart from the one calcined at th...

An extension of the Judd-Ofelt theory, a theoretical model to the field of Luminescence intensity ratio method in phosphor thermometry has been presented, that enables a calculation of thermometric figures of merit: sensitivity, maximum sensitivity and temperature resolution, by the Judd-Ofelt intensity parameters. The model is applicable for 7 out...

Plasma electrolytic oxidation (PEO) of yttrium is performed for the first time and is shown that Y2O3 and trivalent rare-earth ions (Eu³⁺, Er³⁺ or Ho³⁺) doped Y2O3 films can be formed by PEO in alkaline electrolyte without or with addition of rare-earth oxide particles (Eu2O3, Er2O3 or Ho2O3), respectively. The elements present in PEO micro-dischar...

Traditional applications of the Judd-Ofelt (JO) theory to the analysis of the Eu³⁺ optical spectra make use of the emission transitions originating from the ⁵D0 manifold. In the present paper, we report an alternative method of evaluating the JO intensity parameters from the Eu³⁺ emission spectra based on the ⁵D1 → ⁷F0,1 transitions. The reduced ma...

Photoluminescence spectra of bulk YVO4 doped with 1 mol% of Eu³⁺ and Dy³⁺ were recorded on the range from room temperature to 733 K, in 20 K steps. The temperature sensing performances were estimated by the luminescence intensity ratio, line-broadening and line-shift methods. The luminescence intensity ratio was tested by the ratio of intensities o...

Zirconia coatings doped with various contents of Tm³⁺ and Yb³⁺ were formed by the plasma electrolytic oxidation process of zirconium foils for 15 min in alkaline electrolyte containing Tm2O3 and Yb2O3 powders in different concentrations. The coatings were composed of monoclinic and tetragonal ZrO2 phases, but Tm and Yb incorporated into ZrO2 coatin...

Pr³⁺ doped ZrO2 coatings were formed by the plasma electrolytic oxidation (PEO) of zirconium in electrolyte containing Pr2O3 powder. The concentration of a uniformly distributed Pr³⁺ in the coatings increases with time of the PEO process or the concentration of added Pr2O3 powder, causing the stabilization of the tetragonal ZrO2 at the expense of t...

A theoretical model for approximate evaluation of CIE chromaticity coordinates from the Judd-Ofelt intensity parameters has been presented. By reviewing the photoluminescence properties of all the lanthanides, the model's applicability was restricted to Nd³⁺, Sm³⁺, Eu³⁺, Tb³⁺ and Dy³⁺. Explicit equations for calculation of CIE coordinates for each...

A complete apparatus for luminescence thermometry has been built comprising a programmable hot-plate up to 400 °C, a hot/cold plate 0 °C-80 °C, a control circuit with thermocouple feedback, a platinum resistance thermometer and an oven for calibration. An original design allowed us to build the apparatus for under 100 $, considerably less than for...

Judd-Ofelt analysis of HfO2:Eu³⁺ with various europium doping concentrations, formed by plasma electrolytic oxidation, had been investigated. Ω2 parameter is increasing, while Ω4 parameter shows no concentration dependence. For the highest europium doping concentration of 0.62 at% Ω2 = 4.03·10⁻²⁰ cm² and Ω4 = 2.26·10⁻²⁰ cm². Radiative transition pr...

Luminescence thermometry on europium doped TiO2 films, prepared by the plasma electrolytic oxidation, was investigated by the Luminescence Intensity Ratio method. The performance of the material for temperature sensing was tested from room temperature to 260 °C. The theoretical fit of the emission intensity ratio of Eu³⁺⁵D1→⁷F1 and ⁵D0→⁷F2 transiti...

In this paper we will be presenting JOES (Judd-Ofelt from Emission Spectra), an application software for calculation of the Judd-Ofelt intensity parameters and derived quantities from the emission spectra of Eu³⁺ doped materials. The program is written to be user friendly and it requires no previous experience in the field of study. This Free and O...

Plasma electrolytic oxidation was used for synthesis of Eu³⁺ doped monoclinic HfO2 coatings on hafnium substrate. Results of photoluminescence (PL) measurements show the existence of two distinct regions: one that is related to the blue emission originating from oxygen vacancy defects in HfO2 and the other one characterized with a series of sharp o...