Synthesis and optical properties of lanthanides doped ultrasmall NaYF₄ markers for bio-medical applications

Aim. To synthesise NaYF₄ nanocrytstals doped or co-doped with different lanthanide ions (Eu, Tb, Gd) and to investigate them optically to achieve efficient optical markers. Methods. Samples have been synthesized by using co-thermolizys method and optical properties have been investigated by using photoluminescence (PL), PL excitation and PL decay spectroscopies. Results. Efficient emission in visible spectra range has been observed for all investigated samples. The excitation mechanism of the main emission centre has been explained. Conclusions. It has been shown that the main excitation mechanism of Eu ions is through energy transfer from Tb or Gd ions. Moreover, it has been shown that obtained by us nanocrystals characterize by strong emission which make them potential as efficient optical markers in biology or medicine. Keywords: optical markers, nanocrystals, lanthanides, NaYF₄.Мета. Синтезувати нанокристали NaYF₄ , леговані або ко-леговані різними іонами лантаноїдів (Eu, Tb, Gd), та дослідити їхні оптичні властивості для отримання ефективних оптичних маркерів. Методи. Зразки синтезували методом спільного термолізису, а оптичні властивості вивчали методом фотолюмінесценції (ФЛ), фотолюмінесцентної спектроскопії збудження і гасіння ФЛ. Результати. Ефективне випромінювання у видимому діапазоні спектра спостерігали для всіх проаналізованих зразків. Пояснено механізм збудження основного емісійного центра. Висновки. Показано, що головним механізмом збудження іонів європію є передавання енергії від іонів тербію або гадолінію. Крім того, встановлено, що одержані нанокристали характеризуються сильною емісією, що робить їх потенційно ефективнішими оптичними маркерами для біології або медицини. Ключові слова: нанокристали, оптичні маркери, лантаноїди, NaYF₄.Цель. Синтезировать нанокристаллы NaYF₄, легированные или колегированные различными ионами лантаноидов (Eu, Tb, Gd), и исследовать их оптические свойства для получения эффективных оптических маркеров. Методы. Образцы синтезировали методом совместного термолизиса, а оптические свойства изучали методом фотолюминесценции (ФЛ), фотолюминесцентной спектроскопии возбуждения и гашения ФЛ. Результаты. Эффективное излучение в видимом диапазоне спектра наблюдалось для всех исследованных образцов. Объяснен механизм возбуждения основного эмиссионного центра. Выводы. Показано, что главным механизмом возбуждения ионов европия является передача энергии от ионов тербия или гадолиния. Кроме того, установлено, что полученные нами нанокристаллы характеризуются интенсивной эмиссией, что делает их потенциально более эффективными оптическими маркерами для биологии или медицины. Ключевые слова: нанокристаллы, оптические маркеры, лантаноиды, NaYF₄

Influence of Annealing on Excitation of Terbium Luminescence in YAlO 3 Films Deposited onto Porous Anodic Alumina

Terbium-doped yttrium-aluminum oxide films were synthesized by spin-on deposition on porous anodic alumina grown on a silicon wafer and annealed from 400 to 1100°C. An influence of the annealing temperature on the terbium photoluminescence ͑PL͒ was studied using two-dimensional PL excitation and time-resolved spectroscopy. Further, a comparison of thermal quenching data for the most intensive 5 D 4 → 7 F 5 luminescence band of Tb 3+ ions was performed for 10-300 K. From the resultant data, the mechanisms of Tb excitation and its dependence on the annealing conditions are proposed and discussed. © 2010 The Electrochemical Society. ͓DOI: 10.1149/1.3373123͔ All rights reserved. The development of advanced light-emitting materials has received growing interest in recent years. The main requirements imposed on a light source are high emission efficiency, low power consumption, stability in different environments, and low cost of production. One of the solutions that meets these requirements is emitters doped with rare-earth ͑RE͒ ions. The emission wavelengths of different RE ions, playing the role of doping impurities in diverse host materials, cover a broad optical range from UV to IR. As a result, RE-doped materials have already found many applications, e.g., in large-sized displays, environmental-friendly lamps, lasers, and amplifiers. Yttrium-aluminum oxides, particularly yttrium-aluminum garnets, doped with RE, are considered as an important class of lightemitting materials due to their remarkable optical and mechanical properties. Several low cost chemical routes and deposition techniques have been proposed for the fabrication of coatings from these light-emitting materials, reducing the necessary power consumption compared with solid-state synthesis. Among them are spray pyrolysis of the solution of salts, 2 coprecipitation, 3 and sol-gel synthesis. 4 The sol-gel technique, when usually metallorganic precursors are used as one of the components of a sol, avoids treatment at high temperatures. However, the presence of residual carbon-and hydrogen-containing groups in bulk or spin-on fabricated xerogels 10 Experimental In the experiments, superpure aluminum was magnetronsputtered onto a planar side of a polished wafer of monocrystalline silicon. Aluminum was completely anodized in a 1.2 M orthophosphoric acid solution at a constant temperature of 17°C and a constant voltage of 130 V. From scanning electron microscopy, the PAA thickness was 9 m, and the average pore diameter was 140 nm. Yttrium-alumina oxides were prepared by stage-by-stage dissolution of nitrate salts ͑Sigma-Aldrich͒ Y͑NO 3 ͒ 3 ·4H 2 O ͑99.99% purity͒, Al͑NO 3 ͒ 3 ·9H 2 O ͑98% purity͒, and Tb͑NO 3 ͒ 3 ·5H 2 O ͑99.9 purity͒ in an aqueous-alcoholic solution, with pH adjusted to 2 with diluted nitric acid. As a stabilizer, citric acid in the molar ratio ͓metal ions͔/͓citric acid͔ = 1/3 was used. Terbium-containing solution was deposited on PAA by sequential spinning at a rate of 2700 rpm, followed by drying at 200°C, and a final 30 min annealing at temperatures up to 1100°C. The average size of the sample was about 1 ϫ 1 cm. Incident light from the xenon lamp ͑450 W͒ from the monochromator ͑Jobin Yvon TRIAX 180͒ was focused on the sample. The photoluminescence ͑PL͒ and the photoluminescence excitation ͑PLE͒ signals were collected and transmitted by an optical fiber to the spectrometer ͑HR4000 Ocean Optics͒ and were divided by the light source characteristic. The flash xenon lamp and strobe detector coupled with monochromators were used to observe the timeresolved spectra. The X-ray spectra were collected by a Philips diffractometer supported by the parallel beam optic and Cu K␣1 radiation source, = 0.15406 nm. Results and Discussion Structural data.- Emission spectra.-The PL spectra of Tb-doped yttriumalumina oxide/PAA film structures annealed within 400-1100°C obtained for the excitation wavelength of 266 nm are shown i

Influence of annealing temperature on the electron-lattice coupling strength in terbium doped yttrium alumina perovskite xerogels embedded in nano-porous anodic alumina

a b s t r a c t Terbium doped YAlO 3 xerogels were synthesized and spin-coated onto porous anodic alumina substrates. After deposition the films were annealed at temperatures between 400 and 1000°C. The influence of the annealing temperature on terbium emission and the terbium excitation mechanism were investigated by means of photoluminescence, photoluminescence decay and photoluminescence excitation spectroscopy. It was found that both photoluminescence lifetime and the energy difference between spin-forbidden and spin-allowed 4f-5d transitions decreases with the annealing temperature drop. This dependence was correlated to the electron-lattice coupling strength calculated as a function of annealing temperature

Influence of neodymium concentration on excitation and emission properties of Nd doped gallium oxide nanocrystalline films

International audienceGallium oxide and more particularly β-Ga2O3 matrix is an excellent material for new generation of devices electrically or optically driven as it is known as the widest band gap transparent conductive oxide. In this paper, the optical properties of neodymium doped gallium oxide films grown by magnetron sputtering have been analyzed. The influence of the Nd ions concentration on the excitation/emission mechanisms of Nd ions and the role of gallium oxide matrix have been investigated. The grain size reduction into gallium oxide films have been observed when concentration of Nd increases. It has been found for all samples that the charge transfer is the main excitation mechanism for Nd ions where defect states play an important role as intermediate states. As a consequence Nd emission efficiency increases with temperature giving rise to most intensive emission at 1087 nm at room temperature

Simple two-step covalent protein conjugation to PEG-coated nanocrystals

Covering of nanocrystals (NC) with a polyethylene glycol (PEG) envelop is a common way to increase their hydrophilicity, and compatibility with bio-systems, including increased retention time in the body. Colloidal semiconductor NC, also known as quantum dots (QD), particularly benefit from covering with PEG due to passivation of the inorganic core, while maintaining physical properties of the core. Despite many advantages of covering the surface with PEG, the covalent attachment of protein to hydroxyls of PEG is complicated. Here we propose a simple two-step approach for modification of PEG residues with subsequent covalent attachment of proteins. We were able to achieve specific NC targeting by means of attached protein as well as preserve their optical parameters (fluorescence intensity) in chemical reaction conditions. In the optimized protocol, ensuring removal of chemical byproducts by dialysis, we were able to omit the need for centrifugation (usually a limiting step due to particle size). The obtained NC-protein conjugate solutions contained 0.25x of initial unmodified NC amount, ensuring a low dilution of the sample. During all reactions the pH range was optimized to be between 6 to 8. The proposed approach can be easily modified for covalent targeting of different PEG-covered nanocomposites with proteins

Controlled synthesis of tuned bandgap nanodimensional alloys of PbS xSe1-x

Truly alloyed PbSxSe1−x (x = 0−1) nanocrystals (∼5 nm in size) have been prepared, and their resulting optical properties are red-shifted systematically as the sulfur content of the materials increases. Their optical properties are discussed using a modified Vegard’s approach and the bowing parameter for these nanoalloys is reported for the first time. The alloyed structure of the nanocrystals is supported by the energy-filtered transmission electron microscope images of the samples, which show a homogeneous distribution of sulfur and selenium within the nanocrystals. X-ray photoelectron spectroscopy studies on ligand-exchanged nanocrystals confirmed the expected stoichiometry and various oxidized species