Synthesis and properties of rare-earth ion doped yttrium-oxide light sources

Fosfori dopirani jonima retkih zemalja predstavljaju jednu od najznačajnijih klasa luminescentnih materijala. Među njima, itrijum oksid sa svojim veoma dobrim svojstvima, dopiran jonima lantanoida predstavlja odličan izbor za brojne primene ovih materijala. Zbog toga su metode sinteze za dobijanje nanočestica itrijum oksida sa tačno određenom strukturom i morfologijom od presudnog značaja za unapređenje funkcionalnih karakteristika materijala. U okviru ove teze nanostrukturni prahovi na bazi itrijum oksida sintetisani su na četiri načina sledećim metodama: sprej piroliza, hidrotermalna metoda, metoda polimerno-kompleksnog rastvora i metoda samostalno-propagirajuće reakcije na sobnoj temperaturi. Sintetisani su sistemi anti-štoks (Y2O3:Yb3+/Er3+, Y2O3:Yb3+/Ho3+, Y2O3:Yb3+/Tm3+) i štoks materijala (Y2O3:Eu3+ i Y2O3:Sm3+). Ispitana je struktura i fazni sastav sintetisanih prahova, uticaj različitih sinteza i njihovih procesnih parametara (temperatura i vreme termičkog tretmana) na morfologiju prahova. Analiziran je uticaj različitih dopanata i različitih međusobnih odnosa dopanata kod anti-štoks materijala, kao i različita koncentracija dopanata kod štoksovih materijala i njihov uticaj na optička svojstva. Merena su optička svojstva na niskim temperaturama u cilju određivanja potencijalne aplikacije materijala u termometriji. Rendgeno-strukturna analiza svih sintetisanih prahova pokazala je da žareni uzorci imaju dobru kristaliničnost i odgovarajući fazni sastav. Svi sistemi kristalisali su u biksbitnoj fazi kubnog tipa sa prostornom grupom Ia-3. Strukturna utačnjavanja rađena su Ritveldovom metodom u programu Topas Akademik. Najmanja veličina kristalita za žarene uzorke dobijena je metodom polimerno-kompleksnog rastvora (~20 nm), dok je najveća dobijena pri sintezi metodom sprej pirolize (~ 130 nm). Morfologija uzoraka snimana je na transmisionom i skenirajućem elektronskom mikroskopu sa energetsko-disperzionom spektroskopijom X-zraka. Utvrđeno je da se metodom sprej pirolize dobijaju sferne čestice veličine oko 600 nm koje se sastoje od primarnih čestica veličine oko 50 nm. Kod hidrotermalne sinteze na nižoj temperaturi žarenja (600 ºC) dobijaju se čestice izduženog oblika sa dužinom oko 1 μm i širinomoko 100 nm, dok su na višoj temperaturi žarenja (1100 ºC) čestice štapićastog oblika i posledica su procesa kolizije sfernih nanočestica veličine oko 100 nm. Metoda polimerno-kompleksnog rastvora daje aglomerisane čestice sa veličnom od oko 30 nm. Metodom samostalno-propagirajuće reakcije na sobnoj temperaturi naknadnim termičkim tretmanom na temperaturama od 600-1100 ºC morfologija čestica menjala se od štapićastog oblika širine oko 5-10 nm i dužine oko 100 nm pa sve do sfernog oblika čija je veličina čestica oko 50 nm....Phorphors doped with rare earth ions are a major class of luminescent materials. Among them, yttrium oxide with its excellent properties, doped with lantanoide ions represent a great choice for many applications of these materials. Therefore, the synthesis methods for obtaining nanoparticles with precisely defined structure and morphology are of crucial importance for the improvement of materials functional characteristics. In this thesis, nanostructured powders based on yttrium oxide were synthesized by four different methods: spray pyrolysis, hydrothermal method, polymer-complex solution and self-propagating room temperature reaction. Following systems were made: up-convertors (Y2O3:Yb3+/Er3+, Y2O3:Yb3+/Ho3+, Y2O3:Yb3+/Tm3+) and down-convertors (Y2O3:Eu3+ i Y2O3:Sm3+). The structure and phase composition of synthesized powders were examined, as well as the influence of different synthesis methods and process parameters (temperature and heat treatment time) on the morphology of powders. The investigation was also focused on the influence of different dopants and various ratios of dopants in an up-converter, different concentrations of dopants in down-converters and their impact on the optical properties. Emission properties at low temperatures were measured in order to determine the potential application of materials in luminescence thermometry based on luminescence intensity ratio method. X-ray structural analysis of the synthesized powders showed that the annealed samples have good crystallinity and the corresponding phase composition. All systems are crystallized in the cubic bixbyite C-type phase with space group Ia-3. Structural refinement was performed by the Rietveld method in Topas Academic software. The minimum size of the crystallites in annealed samples is obtained by the polymer-complex solution method (~ 20 nm), while the highest was obtained in the spray pyrolysis synthesis (~ 130 nm). The morphology of samples was recorded in transmission and scanning electron microscopy with energy-dispersive X-ray spectroscopy. It was found that with spray pyrolysis method obtained particles are spherical with size of about 600 nm and that v they consist of primary particles with size of 50 nm. Using hydrothermal synthesis at a lower annealing temperature (600 °C) obtained particles had elongated shape with a length of about 1 μm and a width of about 100 nm, while at the higher annealing temperature (1100 °C) particles were rod-shaped, which is a consequence of the collision process of spherical nanoparticles with size of approximately 100 nm. Polymer complex solution method gives agglomerated particles of about 30 nm. Self-propagating room temperature reaction method showed change in morphology at additionally thermally treated temperatures 600-1100 °C, from rod-shaped with width of about 5-10 nm and a length of about 100 nm, to a spherical shape with a particle size of about 50 nm..

Photocatalytic activity of SrGd2O4 down and up-convertor systems

Issues with air and water pollution have become a worldwide problem. Photocatalysis is a technique that holds promise for resolving these urgent issues due to its sustainability, affordability, and environmental friendliness. Recently, anti-Stokes and Stokes luminescence materials have been identified as potentially efficient candidates for photocatalysis exploitation. Under irradiation, doping different Ln3+ ions in an inorganic host will induce designable down and up-conversion emissions beginning in the UV and extending to the NIR region. This investigation will examine the photocatalytic application of the chosen samples. All samples were successfully prepared via sol-gel assisted combustion method. X-ray Powder Diffraction pattern proved that all samples crystallize as a pure orthorhombic phase of SrGd2O4. Scanning and transmission electron microscopy was used for morphology characterization and it revealed the existence of porous agglomerated round-shaped particles favorable for photocatalytic application. Energy Dispersive X-ray Spectroscopy showed the presence of dopant ions and even distribution of all constituting elements. Under simulated solar light irradiation, the photocatalytic characteristics of down-convertors were investigated in the photocatalytic degradation of organic dye methyl orange (MO). During the experiment, a UV/Vis spectrometer was utilized to measure a drop in MO concentration in water solutions. Aliquots of the working solutions were taken at precise time intervals, and the results show that the dye breakdown rate was successful after 4 hours. Methylene blue (MB), as a test pollutant, was used to investigate its photocatalytic efficiency under irradiation of simulated sunlight of up-conversion samples. The obtained results were encouraging because more than 50% of the starting dye concentration was mineralized after 4 hours of exposure to the simulated Sun irradiation.XI Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 18-20, 2023; Belgrad

Influence of the water flow lens system on performances of the different laboratory made Sb2S3-based and commercial solar cells

Here, the behavior of different types of solar cells at a low light intensity, measured with and without using the water flow lens (WFL) system is investigated. This system enables the cooling of the surface of the solar cell/modules/panels, indirectly cooling the surrounding, and allows investigating of the influence of higher or lower intensities of the light with the inevitable change in the spectrum. All of these effects are very important and can greatly contribute to the better photovoltaic performance of the observed cells. In this study, laboratory-made and commercial solar cells were studied at 5 % sun and (or) 35 % sun using a tungsten and halogen lamp, respectively. Comparing the obtained results performed when the WFL system is used and left out, it was confirmed that the WFL system facilitates obtaining better photovoltaic properties for all investigated solar cells.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Effect of Eu3+ - dopant concentration on structural and luminescence properties of SrY2O4 nanocrystalline phosphor and potential application in dye-sensitized solar cells

SrY2O4 phosphors were doped with different concentrations of Eu3+ (0.5, 1, 2, 4, 8 and 10 at %) in order to investigate the maximal doping concentration of Eu3+ and its implementation in solar cell devices. Samples were synthesized by a combustion method using citric acid and glycine as a fuel. The X-ray diffraction (XRD) patterns confirmed pure phase of SrY2O4. FE-SEM micrographs showed agglomerate phenomenon with spherical-like shape particles and diameter of about 50 nm. Upon excitation with 280 nm, emission spectra were recorded in the range from 450-750 nm and in all samples the same energy transitions were observed D-5(0 )-> F-7(J) (J = 1, 2, 3 and 4) with maximal intensity for sample with 8 at % of Eu3+. That sample was further examined for the purpose of application in solar cell devices and showed high value of efficiency at low light intensities

The Synthesis and Characterization of Yb3+ and Ho3+ Doped SrGd2O4

In this investigation, samples of SrGd2O4 doped with different concentration of Yb3+ (2, 4, 6 at%) ions and constant concentration of Ho3+ (1 at%) were prepared. As for synthesis we chose combustion method assisted with glycine as a fuel and citric acid as a chelator. All samples were burned in the furnace at 500 °C for 1.5h and afterwards additionally thermally treated for 2.5 h at 1000 °C. X-ray diffraction (XRD) showed peaks that correspond to the pure orthorhombic lattice of SrGd2O4, space group Pnma (JCPDS Card No.:01-072-6387). FE-SEM micrographs revealed agglomerated phenomenon with spherical shape and diameter around 200 nm. Energy dispersive X-ray spectroscopy (EDS) verified uniform distribution of all constituting elements in particles. Powders optical characterization include measurement of up-conversion (UC) emission spectra after excitation at 980 nm, as well as up-converted intensity dependence on excitation power. Dominant green emission 5F4, 5S2 → 5 I8 was found in all samples, with the most intense emission with 2 at% of Yb3+ and dependence of intensity of UC emission on excitation power confirmed that green emission is facilitated by energy transfer mechanism with two photons.COIN 2022 : Poster Session

Ispitivanje fotokatalitičkih osobina Er3+ i Yb3+ dopiranog nanopraha stroncijum-gadolinijum-oksida

Cilj ovog istraživanja je da se po prvi put ispita fotokatalitička razgradnja metilen plavog na prahovima SrGd2O4 dopiranim istom koncentracijom Er3+ (0.5 at%) i različitim koncentracijama Yb3+ (1, 2.5 and 5 at%). Difrakcija rendgenskim zracima potvrdila je da uzorci kristališu u čistoj ortorombičnoj fazi. Skenirajuća elektronska mikroskopija je korišćena za ispitivanje morfologije i pokazala je da postojanje poroznih aglomerata sačinjenih od manjih čestica sferičnog oblika. Energetski disperzivna spektroskopija pokazala je prisustvo dopanata kao i uniformnu raspodelu svih elemenata u materijalu. Za izračunavanje energetskog procepa korišćena je metoda UV-VIS difuzione refleksione spektroskopije, kojom je dobijena vrednost od 4,3 eV, kao i još četri dodatne vrednosti na nižim energijama. Fotokatalitička razgradnja metilen plavog praćena je metodom UV-VIS apsorpcione spektroskopije. Dobijeni su zadovoljavajući rezultati jer je pri određenim reakcionim uslovima nakon eksperimenta u trajanju od 4 h pod dejstvom simulirane sunčeve svetlosti, potvrđena razgrađnja više od 50% od ukupne početne koncentracije boje

Mechanochemical activation of starting oxide mixtures for solid-state synthesis of BiFeO3

Bismuth ferrite (BiFeO3) is one of the most researched single-phase multiferroic materials.The Fe2 O 3 and Bi 2 O3 oxides were the starting materials for the synthesis of the single phase BiFeO3 . The preparation of BiFeO 3 was done by solid-state method with slight innovation: first, the oxides were activated separately, not together as usual, by milling in the ball mill and second, the 1% olein acid was added to Bi2 O3 as a surfactant before milling, to prevent its granulation. The adding of the oleic acid to Fe2 O 3 was not necessary, because it did not show granulation during milling. The activated Fe2 O 3 and Bi 2 O3 powders were characterized by granylometric analysis after milling in two steps for 4.5 h. The obtained particle sizes were confirmed by SEM micrographs. Finally, prepared oxide powders were mixed, homogenized and sintered. According to XRD pattern the final phase of Fe2 O 3 - Bi 2 O3 mixture sintered at 7900 C for 4 hours was rhombohedral phase of the R3c space group (JCPDS No. 86-1518) BiFeO3 with less than 4% of Bi-rich secondary phase of Bi 25FeO 40 .IMEC2022 - 1st International Conference on Innovative Materials in Extreme Conditions, 22-23 March 2022, Belgrade, Serbi

Annealing and Doping Concentration Effects on Y2O3: Sm3+ Nanopowder Obtained by Self-Propagation Room Temperature Reaction

In this report, structure, morphology and luminescence of Y2O3:Sm3+ nanoparticles prepared by self-propagating room temperature reaction are presented. This new, simple and cost effective synthesis allows obtaining desired phase composition by mixing appropriate amounts of yttrium and samarium nitrates together with sodium hydroxide. A set of samples is prepared with different Sm3+ concentrations (0.1, 0.2, 0.5, 1 and 2 at %) in order to observe changes of luminescence properties. Also, effects of post synthesis annealing at several temperatures (600 degrees C, 800 degrees C and 1100 degrees C) are analyzed. For all samples X-ray diffraction showed that powders have cubic bixbyite structure (I alpha-3), and TEM analysis showed particles of less than 100 nm. Luminescence emission spectra clearly show peaks characteristic for electronic spin-forbidden transition of Sm3+ ions (4)G(5/2)- GT H-6(5/2), H-6(7/2) and H-6(9/2) centered at 578, 607 and 654 nm, respectively. Emission lifetime values decrease with Sm3+ ion concentration increment, from 1.94 ms for 0.1 at% to 0.97 ms for 2 at%. In addition, enlargement of lifetime value is observed when thermal treatment is done at the highest temperature due to the elimination of luminescence quenching species from the surface of particles

Effect of processing parameters on structural and morphological Y2O3 :Yb3+/Ho3+ powders characteristics

Up-converting yttrium oxide powders doped with Yb3+ and co-doped with Ho3+ were\ud synthesized through hydrothermal processing at 200 °C/3 h. Reverse precipitation of the starting nitrates mixture is performed with the help of ammonium hydrogen carbonate (AHC) solution up to pH 7 or pH 9 prior to hydrothermal treatment. Morphological features of the as-prepared (asp)powders and rare earth oxides obtained after powders additional annealing at 1100 oC (3 and 12 h)are discussed based on X-ray powder diffractometry (XRPD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Structural refinement confirmed generation of the cubic bixbyte-structure (S.G. Ia-3) with non-uniform accomodation of dopants at C2 and S6 cationic sites. SEM revealed that the particles have plate-like or rod-like morphology in dependence of hydrothermal processing (pH). Due to the fact that are composed from nanograins (30-100 nm) they demonstrate prominent green luminescence centered at 550 nm after been excited with the infrared laser source (λ=978 nm)

Yb3+/Tm3+ doped SrGd2O4 as photoluminescent and photocatalytic material

In this work we present new up-conversion materials, consisted of SrGd2O4 doped with different concentration of Yb3+ (2, 4, 6 at%) ions and constant concentration of Tm3+ (1 at%), prepared by the combustion method. X-ray powder diffraction (XRPD) showed that assynthesized nanoparticles have orthorhombic structure (Pnma), assigned to the JCPDS Card No:01-072-6387. Scanning electron microscopy (SEM) revealed that obtained nanostructure is composed of porous agglomerated nanoparticles, while energy dispersive spectroscopy (EDS) confirmed presence and uniform distribution of all constituting elements accross the sample. Luminescent properties were evaluated and discovered two blue emission bands at 450 nm and 474 nm, and one red emission band at 650 nm. The sample co-doped with 4 at% Tm3+ showed the most intense photoluminescent emission, and because of that was used in the photocatalytic exiperiment. UV-VIS Diffuse Reflectance Spectroscopy was performed in order to examine materials bandgap, and value of 4.3 eV was obtained as well as the additional values from the bands at lower energies, which indicate potentially good photocatalytic properties. X-ray photoelectron spectroscopy (XPS) revealed presence of OHgroups on the surface which also have positive impact on the photocatalytic performances of the material. UV-VIS Absorption Spectroscopy was used to measure changes of the methylene blue concentration during the photocatalytic degradation process. After 4 h of exposure to the simulating Sun irradiation, the results indicate successful dye decomposition rate. Reaction parameters (MB concentration and catalyst mass) were altered in order to achieve the best photocatalytic performances of this newly synthesized materials.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi