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International audience; Intraband absorption in doped nanocrystals offers an interesting alternative to narrow band gap materials to explore mid infrared optoelectronic device designs. However, the performance of such device clearly lags behind the ones relying on intrinsic materials. Livache et al. have proposed a dye sensitized approach to overcome the limitations observed from intraband materials (high dark current, slow response, low activation energy), where the intraband absorber is coupled to an undoped material which takes care of the charge conduction. Here, we unveil the coupling between both materials using mid-infrared transient reflectivity (TR) measurement. We show that hybrid material displays a unique feature in the TR signal that we attribute to a charge transfer and for which the dynamic matches the hopping time. We then developed a strategy to enhance the photodetection performances of the hybrid material by coupling for the first time intraband absorption to a light resonator. The latter is used to enhance the absorption by a factor 4 and enables an increase of the operating temperature by 80 K compared to the reference device. The obtained device matches the performance of best devices relying on intraband absorption.

Recent experiments on Eu-doped nanocrystals of CsPbX3 (X = Cl, Br) show that Eu exists in the 3+ oxidation state even though it substitutes Pb, which is in the 2+ state in these perovskites. Theref...

Doped nanocrystals such as manganese-doped zinc sulfide (ZnS:Mn) are useful nanomedicine probes for cancer cell labeling and anticancer drug delivery. However, the synthesis and retention of fluorescence of these nanocrystals is highly indispensable for efficient cell theranostics. Herein, we report a modified synthesis of highly fluorescent hydrophobic ZnS:Mn nanocrystals with the advent of dual ligands. Our results demonstrate that the alkylamine ligand with the carbon chain length of C18 promotes the diffusion of Mn from the surface into the interior of ZnS nanocrystals. Optical measurements show that the quantum yield of Mn (QYMn) can reach as high as 80% in the presence of a dual ligand combination of oleylamine-octadecylamine because of the increased probability of 4T1→ 6A1emission, originating from the energy transfer of ligated nanocrystals. These doped nanocrystals after ligand exchange of organic ligands with glutathione exhibited a high retention of quantum yield (QY: ~50-60%), and further coating with silica showed the QY of ~35-40%. Finally, we show the application of these doped nanocrystals for cancer theranostics such as HeLa cell labeling and anti-cancer drug delivery. Agency for Science, Technology and Research (A*STAR) We acknowledge funding from the Joint Council Office, A*STAR, Singapore (grant no. JCOAG03-FG03). We thank the core facilities (XRD, TEM) support staff at the Institute of Materials Research and Engineering (IMRE, Singapore). E.H.A. and S.T.S. acknowledge the National Institution of Education (NIE) and LKC School of Medicine NTU, respectively, for their support in completing and publishing this work.

Cr3+ doped nanocrystals were examined as a noncontact temperature sensor in a lifetime-based approach. The impact of both the analysis protocols and host materials on the lifetime-based approach was systematically investigated. Temperature-dependent luminescence decay curves were analyzed according to three different procedures (average lifetime approach, double exponential fit and time-gated ratiometric approach). The advantages and drawbacks of each method are discussed. Additionally, the thermal sensitivities derived from the average lifetime approach and the double exponential fit revealed a strong dependence of the thermal sensitivity of the Cr3+ doped nanocrystals on the crystal field strength. In these cases, it was found that the long metal–oxygen distances in the host materials improve the thermal sensitivity of the system. This work reveals the importance of both host materials and analysis procedures in the lifetime thermal sensitivity of Cr3+ doped nanocrystals and opens up an avenue towards their future optimization.

We constructed a core-shell like nanoarchitecture in Yb/Er ion and Yb/Ho SrTiO3 nanocrystal-codoped tellurite-borate glass. We demonstrated that the adverse energy transfer between Er3+ ions in the glass region and Ho3+ ions in the crystal region was effectively prohibited, which permits independent and highly efficient emission from Er3+ and Ho3+ ions.

Correction for ‘Core–shell like glass containing lanthanide doped nanocrystals for efficient luminescence’ by Qunhuo Liu et al., Chem. Commun., 2018, 54, 13092–13095.

Improving luminescence efficiency is of vital importance for applications of rare-earth-doped upconversion materials. Herein, we present highly efficient upconversion nanocrystal, which is brighter than the state-of-the-art Er3+/Yb3+ co-doped core–shell material, through Er3+ heavily doping and 1530 nm excitation. Moreover, upconversion characteristics and mechanisms of Er3+ heavily doped core nanocrystals and their core–shell counterparts are investigated carefully.

International audience; Rare earth doped nanocrystals have been recently suggested as useful materials for applications in quantum information processing. To reach optical properties closer to bulk crystals ones, it is still necessary to reduce the defects that can arise in nanoscale structures. Here, we probe the defects level by monitoring the inhomogeneous broadening of the 7 F 0  5 D 0 transition in particles of 0.3% Eu 3+ :Y 2 O 3. We find that lines as narrow as 14 GHz (0.015 nm), a value comparable to single crystals, can be obtained in 150 nm particles calcinated at 1200°C. The additional broadening observed for particles calcinated at lower temperature is attributed to defects inside crystallites and not to surface effects. A linear correlation is also observed between optical and Raman linewidths, suggesting that both processes are sensitive to the same defects. 5 D 0 excited state lifetimes are well described by a model based on an effective refractive index and we conclude that the defects causing the inhomogeneous broadening have no effect on the excited state population.

We consider the translational optical cooling of Yb3+-doped nanocrystals by Raman optical pulses. We describe the coherent interaction between the optical pulses and impurity ions and estimate the temperature corresponding to the nanocrystal’s transition into the macroscopic quantum state. Our cooling scheme can be applied in the fundamental studies on the properties of solid matter.

Biological thiols are antioxidants essential for the prevention of disease. For example, low levels of the tripeptide glutathione are associated with heart disease, cancer, and dementia. Mn2+-doped wide bandgap semiconductor nanocrystals exhibit luminescence and magnetic properties that make them attractive for bimodal imaging. We found that these nanocrystals and silica-encapsulated nanoparticle derivatives exhibit enhanced luminescence in the presence of thiols in both organic solvent and aqueous solution. The key to using these nanocrystals as sensors is control over their surfaces. The addition of a ZnS barrier layer or shell produces more stable nanocrystals that are isolated from their surroundings, and luminescence enhancement is only observed with thinner, intermediate shells. Tunability is demonstrated with dodecanethiol and sensitivities decrease with thin, medium, and thick shells. Turn-on nanoprobe luminescence is also generated by several biological thiols, including glutathione, N-acetylcysteine, cysteine, and dithiothreitol. Nanoparticles prepared with different ZnS shell thicknesses demonstrated varying sensitivity to glutathione, which allows for the tuning of particle sensitivity without optimization. The small photoluminescence response to control amino acids and salts indicates selectivity for thiols. Preliminary magnetic measurements highlight the challenge of optimizing sensors for different imaging modalities. In this work, we assess the prospects of using these nanoparticles as luminescent turn-on thiol sensors and for MRI.

We discuss the novel idea for direct terahertz pulse stimulated emission in the MPO 4 (M = Nd3+, Dy3+) rare-earth doped nanocrystals as a result of transitions between crystal-field (Stark) levels of the Nd3+ and Dy3+ manifolds.

Doped nanocrystals of NaYF(4) and NaGdF(4) are currently studied as upconversion luminescence markers and magnetic resonance imaging contrast agents. An EPR investigation on the growth mechanism of NaYF(4):Gd and NaGdF(4) nanocrystals showed that these nanomaterials grow in the standard oleic acid-based reaction medium by a dissolution/recrystallization mechanism and not by the aggregation or oriented attachment of smaller particles.

Insertion of just a few impurity atoms in a host semiconductor nanocrystal can drastically alter its phase, shape, and physical properties. Such doped nanomaterials now constitute an important class of optical materials that can provide efficient, stable, and tunable dopant emission in visible and NIR spectral windows. Selecting proper dopants and inserting them in appropriate hosts can generate many new series of such doped nanocrystals with several unique and attractive properties in order to meet current challenges in the versatile field of luminescent materials. However, the synthesis of such doped nanomaterials with a specific dopant in a predetermined host at a desired site leading to targeted optical properties requires fundamental understanding of both the doping process as well as the resulting photophysical properties. Summarizing up to date literature reports, in this Perspective we discuss important advances in synthesis methods and in-depth understanding of the optical properties, with an emp...

Because of the potential applications of lanthanide-doped nanocrystals in display devices, optical communication, solid-state lasers, catalysis, and biological labeling, the controlled synthesis of these new nanomaterials has sparked considerable interest. Nanosized phosphorescent or optoelectronic devices usually exhibit novel properties, depending on their structures, shapes, and sizes, such as tunable wavelengths, rapid responses, and high efficiencies. Thus, the development of facile synthetic methods towards high-quality lanthanide-doped nanocrystals with uniform size and shape appears to be of key importance both for the exploration of their materials properties and for potential applications. This Account focuses on the recent development in our laboratory of the synthesis and applications of lanthanide-doped nanocrystals. Since 2005, when we proposed a general strategy for nanocrystal synthesis via a liquid-solid-solution process, a range of monodisperse and colloidal lanthanide-doped fluoride, oxide, hydroxide, orthovanadate, thiooxide, borate, and phosphate nanocrystals have been successfully prepared. By rationally tuning the reaction conditions, we have readily synthesized nanostructures, such as hollow microspheres, nanorods, nanowires, hexagonal nanoplates, and nanobelts. By adjusting the different colloidal nanocrystal mixtures, we fabricated unique binary nanostructures with novel dual-mode luminescence properties through a facile ultrasonic method. By tridoping with lanthanide ions that had different electronic structures, we successfully achieved β-NaYF(4) nanorods that were paramagnetic with tuned upconversion luminescence. We have also used NaYF(4):Yb(3+)/Er(3+) conbined with magnetite nanoparticles as a sensitive detection system for DNA: NaYF(4):Yb(3+)/Er(3+) and Fe(3)O(4) nanoparticles were modified with two different DNA sequences. Then, the modified NaYF(4):Yb(3+)/Er(3+) nanoparticles were conjugated to the modified Fe(3)O(4) nanoparticles. These binary nanoparticles can be hybridized with a third DNA (target DNA) molecule and separated with the assistance of a magnetic field. In addition, a novel fluorescence resonance energy transfer (FRET) method for nonenzymatic glucose determination has been developed by using the glucose-modified LaF(3):Ce(3+)/Tb(3+) nanocrystals. By using bioconjugated NaYF(4):Yb(3+)/Er(3+) nanoparticles as the energy donor and bioconjugated gold nanoparticles as the energy acceptor, we successfully developed a simple and sensitive fluorescence resonance energy transfer (FRET) biosensor for avidin. Meanwhile, we also carried out preliminary studies to investigate possible applications of lanthanide-doped nanocrystals in catalysis and in dye-sensitized solar cells.

Light-emitting Mn-doped semiconductor nanocrystals have been extensively studied for the last three decades for their intense and stable Mn d–d emission. In principle, this emission should be fixed at 585 nm (yellow), but recent studies have shown that the emission can be widely tuned even to 650 nm (red). This is a spectacular achievement as this would make Mn-doped nanocrystals efficient and tunable light emitters. Keeping these developments in view, the chemistry of the synthesis of these materials, their photophysical processes and the expected origins of their red emission are summarized in this Minireview. All the related important studies from 1992 onwards are chronologically discussed, and one particular case is elaborated on in detail. As these materials are potentially important for biology, and photovoltaic, sensing and light-emitting devices, this Minireview is expected to help researchers investigating the chemistry, physics and applications of these materials.

The upconversion luminescence is one of the most significant parameters of upconversion nanoparticles. It is very important for various practical applications, such as bio-imaging, bio-sensing, multiplexed encoding, and so on. This chapter focuses on the upconversion luminescence of the lanthanide-doped nanocrystals, including the emission color tunability and the enhancement of the upconversion luminescence of upconversion nanocrystals.

We present results of the theoretical study of optical characteristics for the small-radius optical centers in the subwavelength ellipsoidal nanocrystals embedded in a medium. Analytical expressions are obtained for the electric-dipole and magnetic-dipole decay rates of excitations of optical centers in a magnetodielectric nanocomposite.

We report the improved characteristic emission of Er3+ ions by co-doping wide-band-gap SnO2 nanocrystals (NCs), which as sensitizers of Er3+ ions. It is found that the Er3+-related near infrared emission is enhanced by three orders of magnitude, which can be attributed to the effective energy transfer process occurs between SnO2 nanocrystals and Er3+ ions. Meanwhile, we also prepare the Er3+-Yb3+ co-doped NaYF4 NCs with Gd3+ dopant ions to obtain high-efficiency up-conversion emission by energy transfer from Yb3+ to Er3+. We demonstrate experimentally that Gd3+ dopant ions play key roles in the formation of β-NaYF4 NCs which can improve the energy transfer efficiency from Yb3+ to Er3+ obviously. Consequently, the up-conversion emission is enhanced by more than five times.

Phosphine-initiated cation exchange is a well-known inorganic chemistry reaction. In this work, different phosphines have been used to modulate the thermodynamic and kinetic parameters of the cation exchange reaction to synthesize complex semiconductor nanostructures. Besides preserving the original shape and size, phosphine-initiated cation exchange reactions show potential to precisely tune the crystallinity and composition of metal/semiconductor core-shell and doped nanocrystals. Furthermore, systematic studies on different phosphines and on the elementary reaction mechanisms have been performed.

We have studied the vibrational modes and Raman spectra of P-doped Si nanocrystals using pseudopotential density functional theory and the Placzek approximation. We find that Si nanocrystal vibrations are largely unaffected by the introduction of P dopants. However, the Raman spectra of doped nanocrystals are enhanced relative to those of pristine nanocrystals, and demonstrate a strong dependence on dopant position. Thus, Raman has the potential of being developed as a tool for probing the location of the dopant within the nanocrystal. Our analysis shows that vibrational modes involving atoms in the vicinity of the dopant give the largest contributions to the Raman spectra.

In experiment, doped Ag:ZnSe nanocrystals (NCs) had better stability than that of ZnSe nanocrystals under ambient atmospheres in the presence of air and light illumination. However, it is difficult to explain the mechanism of better stability of Ag:ZnSe nanocrystals from the experiment perspective for doped nanocrystals are more unstable than corresponding pure nanocrystals in general. Using B3LYP/LANL2DZ method, we have investigated the geometrical structures, bonding characters, and molecular orbitals (MOs) of hexagonal and tetrahedral Ag doped ZnSe structures in theory. The results showed that the good stability of Ag:ZnSe nanocrystals can be attributed to the stronger binding between Ag and Se. Moreover, we have proved that Ag doped ZnSe nanocrystals synthesized in experiment should be substituting doped but not vacuity doped. Substituting Ag doped ZnSe molecules have the same configuration as that of the ZnSe structure, but vacuity doped Ag:ZnSe have completely different configuration than ZnSe structure due to the big size of Ag atom. In addition, through contrast of MO of ZnSe and Ag doped ZnSe, we have testified that Ag easily formed bonds with Se. The high binding energy and high probability of forming bonds with Se atom make Ag doped ZnSe nanocrystals have better stability than that of ZnSe nanocrystals.

By programming the synthetic reaction chemistry, stable blue emitting Cu(I) or Ag(I) doped Al(III) co-doped ZnS (Al,Cu:ZnS or Al,Ag:ZnS) semiconductor nanocrystals are designed. Further, the photostability of the obtained intense blue-violet emission is studied, and the effects of doping/co-doping are correlated. Finally, it is revealed that the strong binding surface ligand 1-dodecanethiol and Al(III) co-doping play pivotal roles in achieving such stable blue emitting doped nanocrystals.

Resonant photoluminescence from Si1−xGex alloy nanocrystals as small as 4 nm in diameter embedded in SiO2 thin film matrices was studied. In pure Si nanocrystals, phonon structures were clearly observed, indicating that optical transitions are assisted by momentum-conserving phonons. These structures are quenched by adding a small amount of Ge atoms in Si nanocrystals, i.e., due to the formation of Si1−xGex alloy. Furthermore, the lifetime of the radiative recombination became much faster in doped nanocrystals. These results suggest that Si1−xGex alloy formation leads to a disorder in the translation invariance of the crystalline lattice, thus resulting in the breakdown of the k-conservation rule.

A homogeneous linewidth of $85.6\ifmmode\pm\else\textpm\fi{}4.4\text{ }\text{ }\mathrm{kHz}$ is reported in 60 nm ${\mathrm{Eu}}^{3+}$ doped ${\mathrm{Y}}_{2}{\mathrm{O}}_{3}$ nanocrystals at 1.3 K. This linewidth was measured by two-pulse photon echoes on highly scattering powders using heterodyne detection. Spectral diffusion was also investigated by three-pulse photon echoes and resulted in a limited broadening of the homogenous linewidth of about 250 kHz over $120\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$. Compared to achievable Rabi frequencies, in the range of several MHz, these values show that rare earth doped nanocrystals can be useful for applications in optical quantum information processing.

The properties and applications of nanocrystals doped with transition and rare-earth impurities are reviewed. The high efficiency and ultrafast recombination times observed in these doped nanocrystals make these materials very attractive for optoelectronic applications.

Nanocrystals exhibit interesting optical, electrical, and chemical properties that are not found in their bulk counterparts. Quantum-confinement effects mean that small changes in their size and shape can have significant effects on physical properties and spectroscopy of nanocrystals. Size and shape control has been a hot topic during the development of the field of nanocrystal synthesis. Current success in colloidal chemistry has produced a great variety of nanocrystals with controlled size and shape, which could be used as functional materials for numerous applications. In addition to size and shape control, phase and composition control also provides additional space to tune the properties of nanocrystals. Further exploration on nanocrystal synthesis has led to the preparation of new-generation nanocrystals, including nanocrystal heterostructures and doped nanocrystals. In this chapter, we present an overview of nanocrystal synthesis with an emphasis on the solution synthesis of colloidal semiconductor nanocrystals.

Introducing to medicine and biology concept of optical markers in tremendous way has changed the recent status of these two important disciplines. This was mainly due to strong development in imaging techniques which recently allow us to investigate both static as well dynamic properties of living cells, their components and their interactions with external factors. Recently used molecular markers including organic dyes, fluorescent proteins or chelates containing lanthanide ions have several significant limitations. One of the alternatives for molecular markers are inorganic quantum dots (ie. CdSe, CdS) which are recently commonly used in many academic works. However, even if they are much better from physico-chemical point of view, from the application point of view at this moment they use is still questionable mainly because of their high risk of toxicity and difficulties in obtaining infrared excitation/emission. One of the solutions, combining advantages of both concepts, is to make nontoxic inorganic nanocrystals doped with lanthanide ions (RENCs). In this work, we will present optical (photoluminescence (PL), PL excitation, PL decay, FTIR, Raman) and structural (XRD, HR-TEM) results obtained for NaYF4 and NaGdF4 nanocrystals doped with Eu, Er, Tm and Yb ions. Based on obtained results, we will discuss examples of ion-ion interaction like: cross-relaxation, energy migration or up-conversion [1, 2] and influence of these interactions on resultant emission properties of RENCs. Additionally, we will discuss the effect of the nanocrystals surface and their core-shell geometry on the excitation and emission properties of lanthanides in RENCs [1, 3]. Finally, we will discuss a few examples of potential application of RENCs in bio-medicine. Acknowledgements The authors would like to thank the Polish National Centre for Research and Development for their financial support under the LIDER project No. 014/L-2/10. References [1] A. Podhorodecki, M.Banski, A. Noculak, B. Sojka, G. Pawlik, J. Misiewicz, On the nature of carriers relaxation and ion-ion interactions in ultrasmall b -NaYF4 nanocrystals-effect of the surface, Nanoscale 5 (2013) 429. [2] A. Podhorodecki, M.Banski, J.Misiewicz, M. Afzaal, P. O Brien, D. Cha, X. Wang, The Multicolor light emitters based on energy exchange between Tb and Eu ions co-doped into ultrasmall b -NaYF4 nanocrystals, J.Materials Chemistry 22 (2012) 5356. [3] M. Banski, M. Afzaal, A. Podhorodecki, Jan Misiewicz, Paul O'Brien, Passivation of lanthanide surface sites in ultrasmall NaYF4:Eu3+ nanocrystals, J. Nanoparticles Research 14 (2012) 1228.

We have successfully fabricated doped Cu-TCNQ nanocrystals, using the reprecipitation method involving a chemical reduction process, which took the composition ratio of Cu:TCNQ = 1.3:1 and contained both TCNQ anion and dianion. Interestingly, the doped nanocrystals exhibited a new strong absorption in NIR region, clearly dependent on the content of the TCNQ dianion.