Upconversion Luminescence Of NaYF4 Research Articles

Multi-mode up-conversion emission of Tm@Yb@Er phosphors for color modulation and thermometry

Rare earth doped up-conversion materials play an important role in information security, colorful display and temperature sensing. In this work, the up-conversion luminescence of NaYF4:0.2Tm/20Yb@NaYF4:20Yb@NaYF4:2Er/20Yb phosphors, synthesized by typical co-precipitation method, are investigated under different excitation condition. The emission color of sample can be tuned from yellow to blue-green through changing pump laser from 1550 to 980 nm because the Tm3+ ions in the core cannot be excited by 1550 nm laser. More interesting, the value of red-to-green (R/G) and blue-to-green (B/G) can be finely manipulated by tuning the excitation pulse width and frequency. This phenomenon can be interpreted by different rising processes of the green, red and blue up-conversion emission. In addition, the core-shell structured sample displays a temperature-dependent color change, ranging from blue-green to purple. The green emissions, radiated from thermal coupled levels (2H11/24S3/2), are used in thermometry and the max relatively sensing sensitivity reaches 0.01 K−1 at 303 K. The findings indicate that the core-shell Tm@Yb@Er phosphors, with excitation-dependent and temperature-dependent up-conversion luminescence, have potential applications in information security and temperature sensing.

The impact of high pressure on the number of photons involved in upconversion luminescence of NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles and application as contactless pressure sensor

Inorganic nanomaterials doped with lanthanide ions and exhibiting upconversion (UC) luminescence are leading in research of nonlinear optical materials. Extreme conditions, such as high-pressure compression (in the GPa range), may influence the physicochemical properties of various compounds. In this work, we investigated the optical properties of upconverting NaYF4:Er3+@NaYF4 and NaYF4:Yb3+,Er3+@NaYF4 core@shell nanoparticles (NPs), focusing on the impact of high pressure on the number of photons involved in the UC mechanism. We measured the UC emission spectra of the synthesized NPs under high-pressure conditions, which allowed us to observe the pressure-induced intensity changes, band centroids spectral shifts, and band intensity ratios alterations. Importantly, by measuring the power-dependent UC emission spectra as a function of pressure, we determined and analyzed the number of photons (n) involved in the UC processes for the first time. It turned out that the n value changes with pressure as a result of diverse multi-phonon relaxation processes enhanced under high-pressure conditions. The results show potential adjustment of UC mechanisms with the use of high-pressure. The calculated band intensity ratios were also used for pressure sensing applications, resulting in the relative sensitivity reaching almost ≈20 % GPa−1 for the Er3+-doped core@shell NPs.

Effect of concentration of Er3+ on up-conversion luminescence in NaYF4 embedded oxy-fluoride glass-ceramics under 1550 nm excitation

Oxy-fluoride glass-ceramics (GC) has advantages such as low phonon energy of fluorides and the excellent physical and chemical properties of oxides. Here we report the synthesis of a series of transparent oxy-fluoride GCs with various doping contents of Er3+ (0.2 mol%-10 mol%) synthesized under different temperatures, and their UCL properties under the excitation of 1550 nm laser. We found that Er3+-doped glass matrix with NaYF4 fluoride nanocrystals demonstrated greatly enhanced UCL compared with as-prepared glass. The samples showed red light emission with 3 mol% Er3+ as the optimal doping content. The wavelength of UCL could be fine-tuned by the temperature of heat treatment, and 893 K seems to be the optimal temperature. We also studied the photoelectric conversion characteristics of the optimal Er3+ doped oxy-fluoride GCs with a polycrystalline silicon solar cell under the excitation of a 1550 nm laser as a possible strategy to effectively improve the photo-electric conversion efficiency of solar cells.

Microwave-assisted synthesis and upconversion luminescence of NaYF4:Yb, Gd, Er and NaYF4:Yb, Gd, Tm nanorods

Anisotropic rare earth ion (RE3+) doped fluoride upconversion particles are emerging as potential candidate in diverse areas, ranging from biomedical imaging to photonics. Here, we develop a facile strategy to synthesize NaYF4: Yb, Gd, Er, and NaYF4: Yb, Gd, Tm upconversion nanorods via microwave synthesis route by controlling the synthesis time and compared the optical properties similar nanorods prepared via solvothermal technique. With the increase in synthesis time, the phase of the particle found to change from mixed phase to purely hexagonal and morphology of the particles change mixed phase of spherical and rod-shaped particles to completely nanorods for a synthesis time of 60 min. Further, the intrinsically hydrophobic particles changed to hydrophilic by removal of oleic capping via acid treatment and the amine functionalized silica coating. The upconversion luminescence as well as laser power dependent emission properties of the surface modified particles elucidate that surface modification route influence the upconversion luminescence as well as solvent dependent emission properties. Moreover, the laser power dependent studies elucidate that the upconversion process in a multi-photon process.

NIR triggered NaYF4:Yb3+,Tm3+@NaYF4/CsPb(Br1-x/Ix)3 composite for up-converted white-light emission and dual-model anti-counterfeiting applications

Assembling nanomaterials from two classes with exceptional control at the nanoscale can lead to new nanohybrids with novel properties. Here, we report the tunable up-conversion luminescence properties of CsPb(Br1-x/Ix)3 perovskite nanocrystals (PeNCs) sensitized by NaYF4:Yb,Tm@NaYF4 up-conversion nanoparticles (UCNPs) at 980 nm excitation. The up-conversion luminescence of NaYF4:Yb3+,Tm3+@NaYF4/CsPb(Br1-x/Ix)3 composite demonstrates that the radiative photon reabsorption process is accountable for the UC energy transfer from excited levels of Tm3+-based UCNPs to PeNCs. The long-lived Tm3+ states feed PeNCs carriers with intrinsic lifetimes extending from nanoseconds to microseconds. By varying the UCNPs/PeNCs concentration ratio, the NaYF4:Yb3+,Tm3+@NaYF4/CsPb(Br0.55I0.45)3 composite generates UC white light emission. The near-infrared excited white light-emitting devices are more compatible with human tissues than blue light-excited ones. Therefore, the prototype of UC white light-emitting diode is developed by coupling the UCNPs/PeNCs composite coated glass plate onto a commercial 940 nm-light-emitting diode chip. To overcome the counterfeiting risk that arises in the case of a single fluorescence mode, we developed a simple dual-model strategy based on manipulation of UC and down-conversion luminescence in anti-counterfeiting under 980 nm and 365 nm excitation, which makes it difficult to encrypt the information. In addition, the UCNPs/PeNCs composite exhibited better photostability under near-infrared illumination, retaining 85% of initial photoluminescence intensity, solving the problem of photo-instability.

Thermal Annealing and Doping Induced Tailoring of Phase and Upconversion Luminescence of NaYF4:Yb Er Microcrystals

ABSTRACT The influence of Mn2+ ion concentration (x = 0–20 mol%) as well as the role of thermal-annealing temperature (400–600°C) on the structural as well as luminescence properties of NaYF4:Yb, Er (Y: 78-x%, Yb: 20%, Er: 2%) microcrystals prepared via a coprecipitation method is investigated. The cubic phase of the as-prepared NaYF4:Yb, Er (Y: 78%, Yb: 20%, Er: 2%) was found to remain intact upon the addition of the Mn2+ ions, but the thermal-annealing elucidates that the phase of the sample depends upon the annealing temperature as well as the Mn2+ ion concentration. Among the Mn2+ ion co-doped samples, 3 mol% doped samples dominant to have a maximum positive influence on the upconversion luminescence of the sample, and a further increase in concentration leads to the concentration-induced quenching of the upconversion luminescence. Moreover, the enhancement factor of green (), as well as red () emission, depend upon the annealing temperature, with a maximum enhancement factor of 5 and 3.12 times for the sample annealed at 400°C, 8.6 and 7.25 times for the sample annealed at 500°C, and 6 and 4 times for the sample annealed at 600°C, as compared to Mn2+ ion undoped samples. The maximum emission strength for the green as well as red is observed for the sample annealed at 600°C and co-doped with 3 mol Mn2+ ions. The laser power-dependent study on all the samples shows that the upconversion process is a multi-photon process, predominantly a two-photon process.

Internal OH\u2212 induced cascade quenching of upconversion luminescence in NaYF4:Yb/Er nanocrystals

Internal hydroxyl impurity is known as one of the main detrimental factors affecting the upconversion (UC) efficiency of upconversion luminescence (UCL) nanomaterials. Different from surface/ligand-related emission quenching which can be effectively diminished by, e.g., core/shell structure, internal hydroxyl is easy to be introduced in synthesis but difficult to be quantified and controlled. Therefore, it becomes an obstacle to fully understand the relevant UC mechanism and improve UC efficiency of nanomaterials. Here we report a progress in quantifying and large-range adjustment of the internal hydroxyl impurity in NaYF4 nanocrystals. By combining the spectroscopy study and model simulation, we have quantitatively unraveled the microscopic interactions underlying UCL quenching between internal hydroxyl and the sensitizers and activators, respectively. Furthermore, the internal hydroxyl-involved UC dynamical process is interpreted with a vivid concept of “Survivor effect,” i.e., the shorter the migration path of an excited state, the larger the possibility of its surviving from hydroxyl-induced quenching. Apart from the consistent experimental results, this concept can be further evidenced by Monte Carlo simulation, which monitors the variation of energy migration step distribution before and after the hydroxyl introduction. The new quantitative insights shall promote the construction of highly efficient UC materials.

Near infrared light‐induced photocurrent in NaYF4:Yb3+, Er3+/WO2.72 composite film

AbstractSpectral conversion technology based on NaYF4:Yb3+, Er3+ upconversion nanoparticles was extensively used to improve photovoltaic conversion efficiency of solar cells. However, the response mismatch between absorption of semiconductors and upconversion luminescence (UCL) limits the application of spectral conversion technology. Nonstoichiometric WO2.72 nanoparticles display the broad absorption from visible to near‐infrared region due to the presence of oxygen vacancy, which is overlapped with the UCL of NaYF4:Yb3+, Er3+ nanoparticles. Thus, the combination between NaYF4:Yb3+, Er3+ nanoparticles, and nonstoichiometric WO2.72 provides a possibility for designing a novel UCL spectral converted solar cells. In this work, composite film consisted of NaYF4:Yb3+, Er3+ nanoparticles, and WO2.72 nanofibers was prepared. The UCL of NaYF4:Yb3+, Er3+/WO2.72 film was decreased in contrast to pure NaYF4:Yb3+, Er3+ nanoparticles due to energy transfer from NaYF4:Yb3+, Er3+ nanoparticles to WO2.72 nanofibers. The NaYF4:Yb3+, E3+/WO2.72film exhibits the photocurrent generation upon the 980 nm excitation. This novel UCL spectral converted solar cells based on the broad absorption of defects in the WO2.72 host will provide a novel view for photovoltaic devices.

Enhanced upconversion luminescence in NaYF4:Yb, Er nanoparticles by using graphitic carbon shells

Upconversion nanoparticles (UCNPs) have drawn much attention in the past decade due to their superior physicochemical features and great potential in biomedical. However, practical applications of upconversion luminescence are often limited by its relatively low luminescence efficiency. In this paper, we designed and synthesized NaYF4:Yb, Er nanoparticles using a hydrothermal approach, and thereafter it was coated with a thin layer of graphitic carbon to form a core/shell nanostructure via a controlled chemical vapor deposition process. It is shown that Yb and Er doped in the crystal of NaYF4 in the forms of Yb3+ and Er3+. The thickness of the graphitic carbon shell is close to 0.45 nm, and this corresponds between one and two atomic layers. The graphitic carbon shell not only leads to a significant enhancement in the emission intensity but also provide a longer luminescence decay lifetime compared to bare NaYF4:Yb, Er nanoparticles. Our finding provides a new strategy to remarkably improve fluorescence upconversion, and opportunities for diverse applications requiring high fluorescence intense.

Particle-size-dependent upconversion luminescence of NaYF4: Yb, Er nanoparticles in organic solvents and water at different excitation power densities

A systematic study of the luminescence properties of monodisperse β-NaYF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles (UCNPs) with sizes ranging from 12–43 nm is presented utilizing steady-state and time-resolved fluorometry. Special emphasis was dedicated to the absolute quantification of size- and environment-induced quenching of upconversion luminescence (UCL) by high-energy O–H and C–H vibrations from solvent and ligand molecules at different excitation power densities (P). In this context, the still-debated population pathways of the 4F9/2 energy level of Er3+ were examined. Our results highlight the potential of particle size and P value for color tuning based on the pronounced near-infrared emission of 12 nm UCNPs, which outweighs the red Er3+ emission under “strongly quenched” conditions and accounts for over 50% of total UCL in water. Because current rate equation models do not include such emissions, the suitability of these models for accurately simulating all (de)population pathways of small UCNPs must be critically assessed. Furthermore, we postulate population pathways for the 4F9/2 energy level of Er3+, which correlate with the size-, environment-, and P-dependent quenching states of the higher Er3+ energy levels.

Upconversion luminescence enhancement of NaYF4:Yb3+,Er3+ nanocrystals induced by the surface plasmon resonance of nonstoichiometric WO2.72 semiconductor

AbstractUpconversion luminescence of rare‐earth ions doped nanoparticles can be enhanced by the localized surface plasmon resonance (LSPR) of noble metals nanoparticles, which was extensively investigated. The semiconductor nanomaterials such as the WO2.72 exhibited the tunable LSPR, which provide the possibility for the luminescence enhancement of upconversion nanoparticles. In this work, the urchin‐like WO2.72 was successfully prepared by solvothermal method, exhibiting the LSPR in the near infrared region. The influence of LSPR of WO2.72 on the upconversion luminescence of NaYF4:Yb3+,Er3+ nanoparticles was investigated firstly. The 525, 542, and 660 nm upconversion luminescence of NaYF4: Yb3+,Er3+ nanoparticles was increased by the 10, 8, and 12 factors, respectively, which was from the enhanced excitation field induced by the WO2.72 film.

Quantum control and enhancement of multi-color emissions in upconversion nanoparticles

Upconversion luminescence (UCL) of lanthanide-doped nanomaterials is usually a low-efficiency nonlinear process, involving multi-step, multi-channel transitions in a multi-level system. Here, we demonstrate quantum control and enhancement of multi-color (e.g., red and green) UCLs of NaYF4:Yb3+/Er3+ nanoparticles with metallic Fabry-Perot micro-cavities. Besides realization of controlled single-color UCLs, their internal quantum efficiencies are strongly enhanced, up to 3–4 orders of times. Experimental results indicate that the controlled single-color UCLs and enhancements are caused not only by modifications of the spontaneous radiation rates for the red- and green-color transitions but also by influencing the intermediate transitions to result in modified distributions of electrons in each of the multiple Er3+ levels, facilitating emission of either red- or green-color light. This work suggests a way to control photon emissions in systems with multi-channel transitions and/or multi-step excitations.

Depleted upconversion luminescence in NaYF4:Yb3+,Tm3+ nanoparticles via simultaneous two-wavelength excitation.

We report optical depletion of upconversion luminescence (UCL) in NaYF4:Yb3+,Tm3+ nanoparticles excited simultaneously by 980 nm and 1550 nm lasers. The UCL intensity is greatly depleted, while the downshifted emission at 1210 nm is obviously enhanced. The disturbances of 1550 nm photons on energy transfer between Yb3+ and Tm3+, cross relaxation (CR), the thermal effect and the stimulated emission depletion (STED) process are qualitatively evaluated. Our investigations verify that the unexpected depletion phenomena are governed by the STED process. The power densities of the 980 nm and 1550 nm lasers are both less than 100 W cm-2, which will greatly reduce the thermal effect and damage and extend the applications of such nanomaterials. These results provide keen insights into controlling emission colors in optical processes, and offer potential applications in multicolor displays and STED nanoscopy.

Accurate thermometry based on the red and green fluorescence intensity ratio in NaYF4: Yb, Er nanocrystals for bioapplication.

A biological temperature measurement method based on the fluorescence intensity ratio (FIR) was developed to reduce uncertainty. The upconversion luminescence of NaYF4:Yb, Er nanocrystals was studied as a function of temperature around the physiologically relevant range of 300-330 K. We found that the green-green FIR Fe and red-green FIR (I660/I540) varied linearly as temperature increased. The thermometric uncertainties using the two FIRs were discussed and were determined to be almost constant at 0.6 and 0.09 K for green-green and red-green, respectively. The lower thermometric uncertainty comes from the intense signal-to-noise ratio of the measured FIRs owing to their comparable fluorescence intensities.

Effect of Mn and Cr doping on the up-conversion luminescence from NaYF4:Yb3+,Er3+

The up-conversion luminescence where the absorption of two or more low-energy photons results in emission of a higher-energy photon has been highly effective in certain applications such as bioanalytical assays. Currently one of the most efficient up-converting materials is the NaYF4:Yb3+,Er3+. However, some applications (e.g. solar cells) still require improvement of the up-conversion efficiency in order to have actual practical use. Therefore, it is important to enhance the performance of the materials. In this work, the effect of Mn and Cr doping on the up-conversion luminescence of NaYF4:Yb3+,Er3+ was studied. The materials were prepared using the co-precipitation method and the ratios of the doping ions were optimized for best up-conversion intensity. The as-prepared materials showed very similar sizes and morphologies. Cr co-doping was observed to increase the up-conversion luminescence whereas the addition of Mn resulted in quenching. Up-conversion luminescence was also measured with different excitation power densities and the results suggested that Cr co-doping enables the up-conversion in lower power densities than without Cr co-doping. Furthermore, the reasons for the changes in up-conversion luminescence intensity were discussed.

3d5金属离子共掺杂NaYF4∶Yb,Er纳米晶的上转换发光

3d5金属离子共掺杂NaYF₄∶Yb,Er纳米晶的上转换发光

Enhancement of the red upconversion luminescence in NaYF4:Yb3+, Er3+ nanoparticles by the transition metal ions doping

In recent years, the application of upconversion nanoparticles, especially in vivo, has so far largely been hampered due to the strong tissue absorption of short-wavelength light below 600nm. Therefore, it is an urgent need to carry out some new selective approaches to increase red emission efficiency. This work reports an effective strategy to enhance red upconversion emission of NaYF4:Yb3+, Er3+ nanocrystals by doping with the different concentrations of transition metal ions (Mn2+ or Fe3+). The upconversion emission spectra of the samples demonstrated that the red emissions were significantly enhanced and that different transition metal ions had a distinguishable effect on the red upconversion luminescence. Compared with the pure NaYF4:Yb3+, Er3+ nanoparticles, the red upconversion emission intensity of the nanoparticles co-doped with 10mol% Mn2+ was increased by nearly as high as 14 times. In addition, the red emission intensity was increased by about 24 times, which was observed in the sample co-doped with 30mol% Fe3+. The mechanism of the enhancement was discussed detailedly. Both the improvement of the nanoparticles׳ crystallinity and the redistribution of electron cloud around the Er3+ ions after introducing Mn2+ or Fe3+ were confirmed to be the origin of the improvement. The enhancement in red upconversion luminescence intensity makes the upconversion nanoparticles versatile imaging tools for diagnosis.

Controllable synthesis and upconversion luminescenceof NaYF4:Yb3+, Er3+ nanocrystals

NaYF4 nanorods, and nanoparticles co-doping with Yb3+ and Er3+ were synthesized by hydrothermal method. The effects of doped ion concentration, the ratio of NaF to Ln (NO3)3 and the reactant content on the luminescence properties of the nanocrystals were investigated in detail in this paper. The materials were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence (PL) spectra. The results indicate that a doping level of 20mol% Yb3+ and 2mol% Er 3+ gives the strongest luminescence, and concentration quenching occurs, when Er3+ concentration exceeds 5mol%. Besides, the reaction of temperature and time were also investigated and the results showed that they have an effect on the shape, size, and crystal phase purity of the nanoparticles. The luminescence mechanism for the NaYF4:Yb3+, Er3+ was discussed. Under 980nm excitation, the Er3+ ions doped into NaYF4 samples emitted green fluorescence 520nm (4H11/2→4H15/2), 550nm (4S3/2→4H15/2) and red fluorescence 650nm(4F9/2→4I15/2), which were modified and enhanced by Yb3+ ions.

Upconversion luminescence of NaYF4:Yb,Er nanocrystals with high uniformity

The NaYF4:Yb,Er nanocrystals were synthesized via the thermal decomposition of metal oleate precursors. The nanocrystals in hexagonal structure were highly uniform and in size of 25 nm. The bright upconversion luminescence was observed under the excitation of 980 nm laser and the upconversion emission spectra were investigated at different pump powers. The emission intensity ratio of red light to green light linearly increased with pump power increasing. This result indicated that there existed a large threshold power of saturation pump for the first excitation state in NaYF4:Yb,Er nanocrystals comparing to that in bulk material.

Size dependence of the upconverted luminescence of NaYF4:Er,Yb microspheres for use in ratiometric thermometry.

The size-dependent temperature sensitivity is observed on the upconversion luminescence of NaYF4:Er,Yb microspheres with sizes between 0.7 and 2 μm that are prepared by a poly(acrylic acid)-assisted hydrothermal process. It is found that the fluorescence intensity ratio (FIR) of their green upconversion emissions (with peaks at 521 and 539 nm) is strongly size-dependent at temperatures between 223 and 403 K. As the size of the spheres increases from 0.7 to 1.6 μm, the maximum sensitivity decreases from 36.8 × 10(-4) to 24.7 × 10(-4) K(-1). This effect is mainly attributed to the larger specific surface area of the smaller spheres where a relatively large number of Er(III) ions are located at the surface. This results in an increase in the efficiency of the (4)S3/2 → (2)H11/2 population process of the Er(III) ions due to stronger electron-phonon interactions with increasing T. Heating of the spheres by NIR light is also supposed to cause enhanced electron-phonon interactions in such particles.