On the nature of the stretched exponential photoluminescence decay for silicon nanocrystals

The influence of hydrogen rate on optical properties of silicon nanocrystals deposited by sputtering method was studied by means of time-resolved photoluminescence spectroscopy as well as transmission and reflection measurements. It was found that photoluminescence decay is strongly non-single exponential and can be described by the stretched exponential function. It was also shown that effective decay rate probability density function may be recovered by means of Stehfest algorithm. Moreover, it was proposed that the observed broadening of obtained decay rate distributions reflects the disorder in the samples

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

Size-Dependent Indirect Excitation of Trivalent Er Ions via Si Nanocrystals Embedded in a Silicon-Rich Silicon Oxide Matrix Deposited by ECR-PECVD

Silicon nanocrystals (Si-nc) embedded in a silicon-rich silicon oxide matrix codoped with Er3+ ions have been fabricated by electron-cyclotron plasma-enhanced chemical vapor deposition. Indirect excitation of erbium photoluminescence via silicon nanocrystals has been obtained within a broad pump wavelength range. The influence of different nanocrystal sizes on the excitation transfer from the Si-nc to Er3+ ions is discussed

GaN ceramics obtained by fusing of nanocrystalline GaN powder at high pressures and temperatures as substrate for growth of GaN epilayers

Abstract In this paper, we have grown GaN films by metalorganic chemical vapor-phase epitaxy (MOVPE) on GaN ceramics obtained from nanocrystalline powder of different initial grain sizes. The samples have been investigated by X-ray diffraction (XRD) and photoluminescence (PL). XRD reveals that the MOVPE GaN films are of single-phase wurtzite structure. Also, it has been observed that the PL spectrum is different for the GaN films compared to that for the GaN powder and also depends on the initial grain sizes.

Optical characterisation of silicon nanocrystals embedded in SiO2/Si3N4 hybrid matrix for third generation photovoltaics

Silicon nanocrystals with an average size of approximately 4 nm dispersed in SiO2/Si3N4 hybrid matrix have been synthesised by magnetron sputtering followed by a high-temperature anneal. To gain understanding of the photon absorption and emission mechanisms of this material, several samples are characterised optically via spectroscopy and photoluminescence measurements. The values of optical band gap are extracted from interference-minimised absorption and luminescence spectra. Measurement results suggest that these nanocrystals exhibit transitions of both direct and indirect types. Possible mechanisms of absorption and emission as well as an estimation of exciton binding energy are also discussed

Study of neodymium photoluminescence and energy transfer in silicon-based gels

This paper reports an investigation of the three $^4F_{3/2}$–$^4I_{n/2}$ emissions of Nd${3+} ions in the red and near infrared in silica gel films containing quantum dots of silicon, with comparison to those in pure silica. Measurements of excitation efficiency at various wavelengths and of PL yields as a function of the Nd concentration show that Nd is more soluble in the substoichiometric oxide obtained from triethoxysilane gels and that the energy of excitons in Si clusters is transferred to G levels of the lanthanide, with an effect of enhancement of the$^4F_{3/2}$–$^4I_{n/2}$ emissions