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Development of upconverting nanomaterials which are able to emit visible light upon near-infrared excitation opens a wide range of potential applications. Because of their remarkable photostability, they are widely used in bioimaging, optogenetics, and optoelectronics. In this work, we demonstrate the influence of several experimental conditions as well as a dopant concentration on the luminescence properties of upconverting nanocrystals (UPNCs) that need to be taken into account for their efficient use in the practical applications. We found that not only nanoparticle architecture affects the optical properties of UPNCs, but also factors such as sample concentration, excitation light power density, and temperature may influence the green-to-red emission ratio. We performed studies on both the single-nanoparticle and ensemble levels over a broad concentration range and found the heterogeneity in the optical properties of UPNCs with low dopant concentrations.

Upconverting nanocrystals (UCNC) have recently been subjected to intensive investigation due to their interesting optical properties and high potential for practical applications. Despite the level of attention paid to these materials, very low quantum yield is still an important issue. In order to break through this limitation, understanding of the emission intensity limitation is crucial. In this paper, we investigate the influence of percolation phenomena on the limitation of the emission intensity from NaYF4:Yb3+,Er3+ nanocrystals. We propose a numerical model and support this experimentally at the single nanocrystal level, explaining the influence of Yb3+ concentration on the optical properties of UCNC. Moreover, based on the experimental and numerical results, we explain the existence of the optimal Yb3+ concentration in the core architecture often reported in the literature. All the measurements have been performed using a custom-built wide-field fluorescence microscope to analyze the emission from hundreds of single nanocrystals and thus make analysis independent of UCNC concentration.

Optical imaging holds great promise for the early-stage detection of diseases. It plays an important role in the process of protecting the patient’s health. Most of the organic dyes suffer due to photobleaching, light scattering, short light penetration depth, and autofluorescence of specimen, thus, need to be replaced with alternative nanoprobes emitting light in the optical biological window (700–1350 nm). The group of candidates which can challenged described problems are colloidal quantum dots (e.g. CdSe and PbS) and upconverting nanocrystals (e.g. NaGdF4:Er, Yb). This paper presents comprehensive and systematic studies of the aforementioned probes, using specially designed tissue phantom, and custom-built wide-field fluorescence microscope. We investigated how the absorption and scattering of light at the water, hemoglobin, and intralipid may affect the intensity of luminescence probes and the quality of optical images. We propose a protocol, that could be easily implemented for investigating other nanoprobes that allow for comparison of their optical performance.

International audience; In this work, silicon nitride films containing terbium were deposited by reactive magnetron co-sputtering in a nitrogen enriched plasma and subjected to rapid thermal annealing treatments. The influence of annealing temperature on the emission and absorption properties of these films was investigated by photoluminescence, photoluminescence decay and photoluminescence excitation measurements. An increase in the photo-luminescence intensity and photoluminescence decay time was observed upon annealing for the main 5 D 4-7 F 5 transition of Tb 3+ ions. This observation was attributed to decrease of the non-radiative recombination and increase of the number of excited Tb 3+ ions upon annealing. Moreover, high temperature annealing was found to shift the spectral position of absorption bands observed in the photoluminescence excitation spectra. In general, these excitation spectra were shown to have a rather complicated structure and were decomposed into three Gaussian bands. It was suggested that two of these excitation bands might be due to indirect excitation of Tb 3+ ions via defects and the third excitation band could be due to direct 4f-5d transition.

Upconverting nanocrystals (UCNC) such as NaYF4:Er3+, Yb3+ have been recently a subject of intensive investigation due to their unique optical properties and high potential in applications in biology and medicine as multifunctional diagnostic probes. Despite the level of attention paid to this material, their very low emission quantum yield is still an important problem excluding them from clinical applications. Thus, understanding of UCNC emission intensity limitation together with a development in growth protocols are crucial challenges to bring these materials to clinical practice. One of the main obstacles, which slowdown the progress in this field, is the complicity of the emission quantum yield measurements. Moreover, even the relative emission intensity measurements (from sample to sample), became a very challenging experiment in case of UCNC. These two difficulties make the optimization of growth process and understanding of experimental data very challenging tasks. In this paper, we will discuss the influence of relative ions concentration, size and the shape of UCNC on their optical properties. We will also show our results obtained for a single UCNC, measured however in the wide field mode giving also the possibility of statistical analysis of UCNC properties. These results will include both the optical imaging as well spectroscopic data. With these results we will show, that this type of experiment enables to measure the relative UCNC emission intensity from sample to sample, what allows for optimization of nanocrystals growth as well as enables to understand the physical limitation of UCNC emission intensity. In particular, we will investigate the effects of Yb3+ ions clustering and its impact on NaYF4:Yb3+, Er3+ UCNC emission intensity. We will also support our conclusions with numerical data. Based on our results we will explain the influence of Yb3+ concentration on optical properties of UCNC in details. Moreover, based on obtained experimental and numerical results we will explain the existence of optimal Yb3+ concentration in UCNC often reported in the literature.

Upconverting nanocrystals (UCNC) have recently been subjected to intensive investigation due to their interesting optical properties and high potential for practical applications. Despite the level of attention paid to these materials, very low quantum yield is still an important issue. In order to break through this limitation, understanding of the emission intensity limitation is crucial. In this paper, we investigate the influence of percolation phenomena on the limitation of the emission intensity from NaYF

Terbium doped YAlO3 composites were fabricated by the co-precipitation method in a porous anodic alumina (PAA) films grown on silicon at three different Tb concentrations: 0.23, 0.87 and 2.11 at.%. To investigate the emission thermal quenching for all samples, we measured the emission spectra as a function of temperature in the range from 10 up to 500 K at 266 and 488 nm excitation wavelengths. Based on obtained results we proposed the physical model explaining the mechanism of Tb3+ emission quenching in YAlO3 composites deposited into PAA film.

Silicon nanocrystals embedded in a silicon-rich silicon oxide matrix doped with Er3+ ions have been fabricated by electron cyclotron resonance plasma-enhanced chemical vapor deposition. Indirect excitation of erbium photoluminescence via silicon nanocrystals has been investigated. Temperature quenching of the photoluminescence originating from the silicon nanocrystals and the erbium ions has been observed. Activation energies of the thermally activated quenching process were estimated for different excitation wavelengths. The temperature quenching mechanism of the emission is discussed. Also, the origin of visible emission and kinetic properties of Er-related emission have been discussed in details.

In this work, we will discuss the excitation and emission properties of Tb ions in a Silicon Rich Silicon Oxide (SRSO) matrix obtained at different technological conditions. By means of electron cyclotron resonance plasma-enhanced chemical vapour deposition, undoped and doped SRSO films have been obtained with different Si content (33, 35, 39, 50 at. %) and were annealed at different temperatures (600, 900, 1100 °C). The samples were characterized optically and structurally using photoluminescence (PL), PL excitation, time resolved PL, absorption, cathodoluminescence, temperature dependent PL, Rutherford backscattering spectrometry, Fourier transform infrared spectroscopy and positron annihilation lifetime spectroscopy. Based on the obtained results, we discuss how the matrix modifications influence excitation and emission properties of Tb ions.

Terbium doped YAlO3 composites, with terbium concentrations up to 2.11 at%, were fabricated by co-precipitation in porous anodic alumina films grown on silicon. The presence of the cubic YAlO3 phase was confirmed by x-ray diffraction and FT-IR analysis. The fabricated samples demonstrate photoluminescence (PL) within the range 350?640?nm, which is associated with f?f transitions from the 5D3, 5G6 and 5D4 levels of Tb3+ ion. Additionally, a broad and fast- decaying PL band in the blue range has been observed, which is associated with defect states. Based on PL excitation spectra, the main excitation channel of Tb3+ ions is due to 4f?5d transitions. Excitation bands observed at 235, 270 and 320?nm have been related to the permitted low-spin 5d2 [LS], 5d1 [LS] and forbidden high-spin 5d1 [HS] states, respectively. The PL decay spectra have been measured, with the results analysed using the maximum entropy method; a strong indication of ion?ion interaction has been observed. The distribution of Tb3+ ions in the PAA?:?YAlO3 structure has been proposed and its influence on optical properties of Tb3+ ions has been discussed.