Enhancement Of Upconversion Emission Research Articles

Pressure‐Induced Symmetry Breaking Enables Retainable Upconversion Photoluminescence Enhancement in Lanthanide Oxyfluoride

AbstractPressure‐induced performance enhancement of a given material is an emerging phenomenon, however, among the various known examples very few enhanced properties can retain to ambient conditions. Both new structural mechanism and new material systems are the key challenge to achieve recoverable properties via pressure treatment. Herein, an “Er‐rich” erbium oxyfluoride ErOF is reported with retainable enhanced upconversion (UC) emission by high pressure treatment. The UC emission increases to more than twice the intensity of its pristine state, and followed by additional improvement to 5.1‐fold increase by heat treatment at 100 °C. The site symmetry breaking of Er3+ ions along with the crystal phase transition from Rm to Pnma, revealed by X‐ray diffraction, is believed to be the underlying reasons for the enhanced UC emission after release. Further, high‐resolution transmission electron microscopy (HRTEM) study reveals that the defects relieved with heat treatment might account for the UC emission enhancement in the released sample. Time‐resolved spectra and I‐P curves are measured comparatively to further illustrate the intrinsic mechanism of UC processes. The findings open up a window to advance UC performance through structure optimization by pressure engineering, thus facilitating its potential applications under ambient conditions.

Enhanced upconversion emission in Nd, Yb, Er and Ho tetra-doped Y2O3 phosphor

Yb3+, Nd3+, Er3+ and Ho3+ tetra ions doped Y2O3 upconversion phosphors have been prepared by the combustion route. Crystalline phase purity and cubic phase of prepared samples have been confirmed from powder X-ray diffraction study. Absorbance of samples over spectral range 200–1100 nm has been measured by diffuse reflectance spectroscopy. All samples exhibit large band gaps. Scanning electron micrograph analysis reveals spherical morphology of particles and sizes around 200 nm. Upconversion emission has been studied under a 980 nm diode laser excitation with 166 mW laser power. The Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor show very high emission intensity of a green band centred at around 550 nm and another moderate intensity red band centred on 667 nm, while reverse is the case for Er3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor. Er3+, Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor show enhanced high emission intensity in both green and red bands. These two bands are not visible in Nd3+ and Yb3+ co-doped Y2O3 phosphor but show weak upconversion emission at 549, 568 and 799 nm. Owing to the high emission intensity of green band, Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor may find potential applications in medical and security, while Er3+, Ho3+, Nd3+ and Yb3+ co-doped phosphor showing enhanced upconversion in green and red bands may find applications in white light generation.

Nanocrystals Incorporated with Mordenite Zeolite Composites with Enhanced Upconversion Emission for Cu2+ Detection.

In this research, upconversion nanocrystals incorporated with MOR zeolite composites were synthesized using the desilicated MOR zeolite as a host for the in situ growth of NaREF4 (RE = Y, Gd) Yb/Er nanocrystals. The structure and morphology of the composites were studied with XRD, XPS, and TEM measurements, and the spectral studies indicated that the subsequent thermal treatment can effectively improve the upconversion emission intensity of Er3+. By using the NaYF4:Yb/Er@DSi1.0MOR-HT composite that holds the strongest upconversion emission, a probe of UCNC@DSiMOR/BPEI was constructed with the modification of branched poly ethylenimine for the detection of Cu2+. It was indicated that the integrated emission intensity of Er3+ shows a linear dependence with the logarithm value of the Cu2+ concentration ranging from 0.1 to 10 μM. This study offered a feasible method for the construction of UCNC@zeolite composites with enhanced upconversion emission, which may have a potential application as fluorescent probes for the detection of various metal ions by adjusting the doping luminescent center.

Near infrared emissions from both high efficient quantum cutting (173%) and nearly-pure-color upconversion in NaY(WO4)2:Er3+/Yb3+ with thermal management capability for silicon-based solar cells

Raising photoelectric conversion efficiency and enhancing heat management are two critical concerns for silicon-based solar cells. In this work, efficient Yb3+ infrared emissions from both quantum cutting and upconversion were demonstrated by adjusting Er3+ and Yb3+ concentrations, and thermo-manage-applicable temperature sensing based on the luminescence intensity ratio of two super-low thermal quenching levels was discovered in an Er3+/Yb3+ co-doped tungstate system. The quantum cutting mechanism was clearly decrypted as a two-step energy transfer process from Er3+ to Yb3+. The two-step energy transfer efficiencies, the radiative and nonradiative transition rates of all interested 4 f levels of Er3+ in NaY(WO4)2 were confirmed in the framework of Föster-Dexter theory, Judd-Ofelt theory, and energy gap law, and based on these obtained efficiencies and rates the quantum cutting efficiency was furthermore determined to be as high as 173% in NaY(WO4)2: 5 mol% Er3+/50 mol% Yb3+ sample. Strong and nearly pure infrared upconversion emission of Yb3+ under 1550 nm excitation was achieved in Er3+/Yb3+ co-doped NaY(WO4)2 by adjusting Yb3+ doping concentrations. The Yb3+ induced infrared upconversion emission enhancement was attributed to the efficient energy transfer 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+) and large nonradiative relaxation rate of 4I9/2. Analysis on the temperature sensing indicated that the NaY(WO4)2:Er3+/Yb3+ serves well the solar cells as thermos-managing material. Moreover, it was confirmed that the fluorescence thermal quenching of 2H11/2/4S3/2 was caused by the nonradiative relaxation of 4S3/2. All the obtained results suggest that NaY(WO4)2:Er3+/Yb3+ is an excellent material for silicon-based solar cells to improve photoelectric conversion efficiency and thermal management.

Multi-dimensional tailoring of the thermometric behaviors of Er3+/Yb3+-codoped Y2W3O12 polychromatic upconverting microparticles for multi-mode visual optical thermometry

To combat the thermal quenching and inadequate sensitivities of luminous materials, the Y1.98–2xW3O12:0.02Er3+/2xYb3+ (YWO:Er3+/2xYb3+; 0.01 ≤ x ≤ 0.11) microparticles with splendid negative thermal expansion (NTE) effect were designed. Excited at 980 nm, the produced samples emit polychromatic upconversion (UC) emissions triggered by the energy back transfer from Er3+ to Yb3+ and it has been systematically discussed via steady-state rate theory. The thermally enhanced UC emissions are accomplished in YWO:Er3+/2xYb3+ microparticles due to the distinctive NTE properties. Moreover, according to the temperature-associated UC emissions of Er3+ arising from its thermally coupled levels (TCLs) and non-thermally coupled levels (non-TCLs), the thermometric properties of synthesized microparticles are investigated. When non-TCLs are adopted, the absolute and relative sensitivities of resultant microparticles are 0.0129% and 1.7875% K−1, respectively. Furthermore, through manipulating doping content and spatial mode, the temperature sensing capacities of YWO:Er3+/2xYb3+ microparticles are multi-dimensionally regulated. In addition, contactless temperature recognition can also be realized through analyzing the thermochromic features of final products and its relative sensitivity is 2.1604% K−1. Ultimately, visual optical temperature detection is obtained in designed microparticles via its temperature-related emitting colour. Our findings may provide an important insight into the design of luminescent materials with high sensitivities for multi-mode visual optical thermometry.

Tuning the optical properties of Ln3+-doped-Y2O3@ZnO@Au core-shell heterostructures for visible-to-NIR photon harvesting

Here, compact Yb3+-Er3+-Tm3+ doped Y2O3 phosphor microspheres were synthesized by solvothermal method which gave emission in the entire visible region under 980 nm excitation. The effect of doping alkali ions like lithium on the upconversion emission of YYET phosphors is investigated. An epitaxial layer of ZnO is grown around the YYETL (Li+ doped YYET) microspheres by hydrothermal technique. An analysis of the influence of the ZnO shell thickness on the upconversion emission of core microspheres is done. Initial growth of a thin layer of ZnO on the YYETL microspheres causes enhancement in upconversion emission due to passivation of surface defects of core microspheres. Quenching of anti-Stokes emission occurs for thicker ZnO shell coating. Further, it is decorated with AuNPs to study the effect of plasmonics on the optical property of the developed heterostructure. The overlap between the upconversion emission spectra of core microspheres and the LSPR peak of AuNPs modulates the property of the entire structure. The optimized samples were checked for photocatalytic application by degradation of Rh6G dye under solar irradiation. YYETL@ZnO@Au core-shell samples exhibited highest rate constant of 0.00395 min−1, which is attributed to better exploitation of the UV–Vis-NIR region of the solar spectrum by all three components of the heterostructure.

Flexible composite film with enhanced upconversion emission for ultrasensitive gas detection

Lanthanide-doped upconversion nanoparticles (UCNPs) were found promising in photovoltaic devices and nanoscale sensing due to their excellent optical properties. However, the low quantum yields severely limit their practical applications. In this work, we reported the enhanced upconversion emission by near-field modulation on all dielectric interfaces. The flexible polystyrene (PS) sphere array @UCNPs composite was fabricated by self-assembly and the NIR excitation can be highly localized and amplified in the array with proper sphere size, thus promoting the upconversion process. Based on this efficient upconversion composite film, the sensing performance on acetic acid gas were discussed in detail. The good linear relationship between the upconversion luminescence intensity and acetic acid concentration can be achieved with a detection limit of 5.2 ppm at room temperature, which is comparable with the best level reported so far. In addition, such optical signal-based sensors possessed other unique advantages such as easy fabrication, high sensitivity, long-term stability, reusability and flexibility. And the fluorescence signal enhancement factor showed less dependence on the excitation power and can emit effectively at low pump power. This all dielectric fluorescent composite with high efficiency and sensing performance can be helpful in biosensor and flexible security label applications.

Light Enhancement of Green Up-Conversion Emission from Er-Doped Silica Microspheres by Carbon Quantum Dot Coatings.

Combination of high quality cavity such as glass microsphere and emitting nano-particle coating layers can create novel strongly emitting devices. Herein, we demonstrate an erbium-doped silica microsphere coated by dual-emission carbon quantum dots, which have the sizes of 3-5nm, emitting green up-conversion with narrow line-width green light at wavelength of 537nm. The dual-emission carbon quantum dots fabricated by hydrothermal process and have luminescent emission wavelengths in the range of 410-550nm. The carbon quantum dot coated erbium silica microsphere is pumped at wavelength of 976nm through the optical fibre on which microsphere attached on the tip. The dual-emission carbon quantum dot layers attributed to the strong green up-conversion light enhancement similar coated noble metallic thin films, however the light enhancement from dual-emission carbon quantum dot coated erbium silica microsphere depended on the thickness of coating layers. This result is useful for making visible emitting micro-devices and photonic integrated circuits.

LuF3: Yb3+/Tm3+@Lu6O5F8: Yb3+/Tm3+@BiOI for efficient degradation of pollutants under NIR light: Synergy of enhanced upconversion emission and efficient FRET

Effective use of near-infrared (NIR) light for photocatalysis in the solar full-spectrum remains a major challenge. Herein, LuF3: Yb3+/Tm3+@Lu6O5F8: Yb3+/Tm3+ (LYT@LOYT), which could convert NIR light into UV–visible light, was combined with BiOI to form a novel core-shell structured LuF3: Yb3+/Tm3+@Lu6O5F8: Yb3+/Tm3+@BiOI (LYT@LOYT@BiOI) upconversion photocatalyst. LOYT shell layer was grown in situ on LYT by high-temperature calcination in air, resulting in a 2.36-fold enhancement of blue light emission from the upconversion luminescent core. The tight core-shell wrapping formed by the solvothermal method achieved an efficient Förster resonance energy transfer (FRET) between LYT@LOYT and BiOI. Meanwhile, the formation of heterogeneous structure also accelerated the separation and transfer of photogenerated electron-hole pairs. As a result, under NIR and Vis-NIR irradiation, the degradation rates of LYT@LOYT(20)@BiOI for bisphenol A (BPA) were 1.24 and 1.11 times of LYT(20)@BiOI, and 1.57 and 1.30 times of BiOI, respectively. The enhanced photocatalytic activity was attributed to the expanded photoresponse range, enhanced upconversion emission, efficient energy transfer process, and excellent electron-hole pairs separation transfer efficiency. h+ and ⋅O2- were shown to be active species in the degradation process. This work provides a useful reference for the rational design of solar full-spectrum responsive photocatalysts which can efficiently utilize NIR light.

In situ growth of lanthanides-doped nanoparticles inside zeolites with enhanced upconversion emission for gallic acid detection

The combination of upconversion nanoparticles (UCNPs) with porous zeolites could enable the development of multifunctional composites and extend their optical applications in sensing, detection and biomedical monitoring. Herein, a series of high luminescent UCNPs@Zeolites nano-micro composites were constructed via the in situ growth strategy, by taking the low phonon-energy fluoride nanoparticles of NaLnF4 (Ln = Y, Gd) as doping hosts for Er3+/Yb3+, desilicated FAUY and ZSM-5 as the target zeolites. Benefiting from the formation of tightly combined interfaces between the UCNPs and the target zeolites that effectively passive the surface defects of UCNPs, three orders of magnitude of improved upconversion emission in maximum was obtained under 980 nm excitation through afterward heat treatment at 400 ℃. Moreover, the pre-exchange of Yb3+ into target zeolites before the in situ growth of UCNPs is another feasible approach to drastically improve the upconversion emission intensity of the UCNPs@Zeolites nano-micro composites. By taking NaGdF4:Yb,Er@DSZSM-5/HT as an example probe, the detection of GA was demonstrated and the detection ability of which is super than that of the corresponding bare NaGdF4:Yb,Er UCNPs. This research provided a universal approach to construct the UCNPs@Zeolites nano-micro composites with varied upconversion emission colors simply by choosing activator ions, which therefore indicates wide potential applications.

Electrically Sensitive Plasmonic Photonic Crystals for Dynamic Upconversion Manipulation

AbstractLocal optical field modulation using plasmonic materials or photonic crystals provides a powerful strategy for enhancing upconversion emission of lanthanide‐doped upconversion nanocrystals (UCNPs). However, it is restricted to static UC enhancement and the corresponding dynamic modulation of UC is yet to be reported, limiting its practical applications in information devices. Here, a dynamic UC modulation system is reported through electric stimulation by integrating UCNPs with electrically sensitive WO3−x plasmonic photonic crystals (PPCs). The tunable emission enhancement of UCNPs varying from five to 26 folds is achieved in WO3−x PPCs/UCNPs hybrids through external electric stimulation within +1.6 and −1.6 V. It stems from the reversible control of the photonic bandgaps and localized surface plasmon resonance of WO3−x PPCs, ascribed to the variation of refractive index and oxygen vacancy of WO3−x, induced by the reversible change of atomic ratio of W5+ to W6+ under different applied voltages. Moreover, the electrically triggered information encryption devices are developed, employing a programmable logic gate array based on WO3−x PPCs/UCNPs with the ability to convert information‐encrypted electrical signals into visible patterns. These observations offer a new attempt to manipulate the UC and will simulate the new applications in the display and optical storage devices.

In-situ confinement of ultra-small NaYF4:Yb3+/Er3+ UCNPs as multifunctional ratiometric thermometer and optical heater

Lanthanide-doped upconversion (UC) nanomaterials with zero background auto-fluorescence are of extensive interest in optical fields. Here, a NaYF4:Yb3+/Er3+@Zr-UiO-66 nanostructure was prepared by simultaneously encapsulating NaYF4:Yb3+/Er3+ nanoparticles (NPs) and promoting the nucleation of UiO-66 under solvothermal condition. Traditional nanosize-surface induced defects and grain boundaries of NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) were greatly minimized; enabling a highly efficient energy transfer confirmed by the prolonged fluorescence lifetime and enhanced UC emission of NaYF4:Yb3+/Er3+@Zr-UiO-66 nanocomposite. The optical thermometry property of nanocomposite was investigated based on the fluorescence intensity ratio (FIR) technique in the temperature range of 303–393 K. The maximum relative temperature sensitivities (Sr) were calculated to be 1.02 and 0.73% K−1 based on a pair of thermally coupled energy levels (TCLs) of (2H11/2 → 4I15/2, 4S3/2 → 4I15/2) and another pair of non-thermally coupled energy levels (NTCLs) of (2H11/2 → 4I15/2, 4F9/2 → 4I15/2), respectively. Besides, it exhibited effective internal optical heating property due to the thermal excitation between the two adjacent TCLs of 2H11/2 and 4S3/2 in NaYF4:Yb3+/Er3+ UCNPs as heated by increasing the laser power. This work demonstrates a feasible confined synthesis of NaYF4:Yb3+/Er3+@Zr-UiO-66 nanocomposite with extreme UC emitting performance, and it holds great potential acting as both ratiometric thermometer and optical heater for multifunctional applications.

Multifunctional Laser-Induced Bubble Microresonator for Upconversion Emission Enhancement

Multifunctional Laser-Induced Bubble Microresonator for Upconversion Emission Enhancement

One-pot synthesis of hexagonal NaLuF4:Yb,Er microcrystals with enhanced upconversion emission and high production yield

One-pot synthesis of hexagonal NaLuF4:Yb,Er microcrystals with enhanced upconversion emission and high production yield

Semiconductor Plasmon Enhanced Upconversion toward a Flexible Temperature Sensor.

Noninvasive and sensitive thermometry is crucial to human health monitoring and applications in disease diagnosis. Despite recent advances in optical temperature detection, the construction of sensitive wearable temperature sensors remains a considerable challenge. Here, a flexible and biocompatible optical temperature sensor is developed by combining plasmonic semiconductor W18O49 enhanced upconversion emission (UCNPs/WO) with flexible poly(lactic acid) (PLA)-based optical fibers. The UCNPs/WO offers highly thermal-sensitive and obviously enhanced dual-wavelength emissions for ratiometric temperature sensing. The PLA polymer endows the sensor with excellent light-transmitting ability for laser excitation and emission collection and high biocompatibility. The fabricated UCNPs/WO-PLA sensor exhibits stable and rapid temperature response in the range 298-368 K, with a high relative sensitivity of 1.53% K-1 and detection limit as low as ±0.4 K. More importantly, this proposed sensor is demonstrated to possess dual function on real-time detection for physiological thermal changes and heat release, exhibiting great potential in wearable health monitoring and biotherapy applications.

Enhancement of photoacoustic and upconversion emission in Mg2+/Zn2+ codoped Gd2O3: Er3+/Yb3+ phosphor using 980 nm excitation.

In this work, Er3+/Yb3+ doped Gd2O3 phosphor samples were synthesized through a combustion method and then characterized through X-ray diffraction and FE-SEM techniques. The sample was studied for photoacoustic spectroscopy (PAS) and upconversion (UC) emission spectroscopy techniques using a frequency modulated 980 nm excitation source. A correlation between PA signal (produced due to non-radiative transitions) and UC emission intensity (produced due to radiative transition) is made in order to optimize the sample for both these properties. The phosphor was codoped with Mg2+ and Zn2+ ions to see enhancement in upconversion emission intensity and these ions have enhanced the upconversion emission. Studies show that the present phosphor is appropriate for producing strong upconversion emission intensity along with a strong photoacoustic signal which is beneficial for upconversion-imaging as well as photothermal therapy. The present sample has also shown its potential for detection of fingerprints.

Near-infrared light responsive intensified multiphoton ultraviolet upconversion in nanostructures towards efficient reactive oxygen species generation.

Near-infrared-to-ultraviolet (NIR-to-UV) multiphoton upconversion has recently received increasing attention owing to its promising frontier applications in the fields of biomedicine and nanophotonics. However, the realization of high-efficiency NIR-to-UV upconversion remains a dispiriting challenge due to weak excitation light harvesting and photo-conversion efficiency. Herein, we propose a mechanistic strategy to achieve intensified UV upconversion by manipulating the injected excitation energy flux. A simple LiYbF4:Tm@LiYF4 host-sensitized sublattice core-shell nanostructure was initially proposed to compete with the concentration quenching effect and increase energy transfer efficiency. Then, the organic dye ICG was further coated to introduce the antenna sensitization effect to highly increase the absorption ability of nanocrystals. After optimizing the ICG number loaded on the surface and separation distance, up to 167-fold UV upconversion emission enhancement was achieved under low-power excitation of 808 nm. More importantly, the efficient UV upconversion exhibits enhanced reactive oxygen species (ROS) generation activity by fabricating a TiO2-modified upconversion nanocomposite, revealing great application potential in frontier fields such as in vivo photodynamic therapy and bioimaging-guided therapeutics. Our results can provide versatile designs to achieve efficient UV upconversion, overcome conventional limitations, and offer exciting opportunities for potential applications in biomedical fields.

Enhanced up-conversion emission of fluoride phosphor in the dual-fuel system under 1550 nm excitation

A 1.5 μm multi-component fluoride nanocrystal PbxNay-nLinYzF2x+y+3z+3m: Er3+m was synthesized by the low temperature combustion synthesis (LCS) method. On the basis of the orthogonal experiment and optimization experiment, Li+ ion was introduced into the matrix and the dual-fuel system was established, and the up-conversion luminescence intensity was enhanced by changing the matrix composition and improving the process methods. The results show that when the concentration of Li+ ion is 2.07 mol%, the fuel consumption in the dual-fuel system is 2.2 stoi., 0.7 stoi., the up-conversion luminescence intensity is obviously improved. The structure and morphology of samples were analyzed by the X-ray diffraction (XRD) and scanning electron microscopy (SEM), and a schematic model of physical mechanism for the luminescence intensity of Li+ ion enhanced materials was confirmed. The exothermic characteristics of the dual-fuel system were analyzed by the differential scanning calorimetry and thermogravimetric analysis (DSC-TGA). The influence of the introduction of Li+ ion and the dual-fuel system on the luminescence intensity was discussed in detail.

Collective modulation of upconversion in Ag-BaTiO3: Yb3+, Er3+ by photonic bandgap and surface plasmon resonance effects

A series of Ag-BaTiO3: Yb3+, Er3+ inverse opal structures were synthesized by co-precursor sol-gel method. Under near-infrared excitation, the enhanced upconversion emissions were obtained by the coupling of photonic band gap and surface plasm on resonance effects. The green and red luminescence of Ag-BaTiO3: Yb3+, Er3+ were up to 14.2-fold and 12.8-fold higher than the reference sample, respectively. In addition, a rate equation model has been established based on the energy transfer processes, and a thorough analysis has been conducted to clarify the influence of two effects. By altering the photonic bandgap position, corresponding spontaneous emissions could be inhibited and the efficiency of incident light could be improved. With the introduction of plasmonic structures, the green to red ratio was able to be manipulated by the Purcell factor of radiative decay rate and the additional nonradiative decay channels described by Wnr. This work employs an intriguing strategy for modulating and enhancing upconversion luminescence, which is of great value for potential applications in displays and bio-lables.

Synthesis of LiErF4 and LiGdF4 Core‐Shell Nanocrystals and Tunable Upconversion Emission from Red to Green

AbstractIn this study, LiErF4 and related LiGdF4 core‐shell nanocrystals were synthesized via thermal decomposition, and the upconversion luminescence under an excitation of 980 nm was investigated. The phase of LiErF4 was not changed by a low content of Gd3+ dopant, whereas orthorhombic GdF3 formed as an impurity when the amount of Gd3+ was increased. The upconversion luminescence intensity of LiErF4 was enhanced by a suitable Gd3+ content. Considering the enhanced upconversion emission of LiErF4 and synthesis of pure tetragonal phase LiGdF4, a core–shell structure of LiErF4@LiGdF4:Yb,Er was designed, characterized, and compared to LiYF4@LiGdF4:Yb,Er. LiErF4@LiGdF4:Yb,Er had a yellow upconversion emission output, which was attributed to the combination of the upconversions in the core and shell. Additionally, a series of relevant derivatives of LiErF4@LiGdF4:Yb,Er were prepared for further investigation of their luminescence performance, and red‐to‐green tunable upconversion luminescence was obtained for these core–shell nanocrystals.