NaYF4 Upconversion Nanoparticles Research Articles

Few-mode optical fiber-based flexible pressure feedback tentacle doped with fluorescence temperature pointer

Abstract In this paper, a flexible fiber pressure feedback whisker is proposed, which consists of a water droplet shaped polydimethylsiloxane (PDMS) elastomer with an embedded balloon shaped few mode fiber. The mechanical sensing performance of the device was analyzed and optimized using a combination of finite element method and beam propagation method (BPM). The built-in cladding corroded few-mode fiber increases pressure sensitivity by more than four times. The collection efficiency of fluorescence signal is improved by cladding corrosion. The PDMS elastomer was doped with upconversion nanoparticles NaYF4:Yb, Er@NaYF4 in order to achieve temperature measurement by fluorescence intensity ratio technology. The combination of fluorescence signal and interference spectrum can not only achieve real-time and accurate pressure detection at different temperatures, but also incorporate fluorescent materials into flexible bionic skin for temperature self-compensation, which has potential application value for the development of bionic fiber micro-nano sensing and control devices.

Optimization of the structure, morphology and luminescent properties of NaYF4 upconversion nanoparticles

We designed and constructed rare earth doped upconversion nanoparticles β-Na(Y0.78Yb0.18Er0.04)F4, sensitizing layer encapsulated β-Na(Y0.9Er0.1)F4@β-NaYbF4 and inert layer encapsulated β-Na(Y0.9Er0.1)F4@β-NaYbF4@β-NaYF4. Compared with the mononuclear material, the luminescence intensity of the particles encapsulated with double shells in the three main bands of blue, green and red emissions increased by 346, 22, and 54 times respectively. While improving the upconversion luminescence performance, the underlying reasons for this improvement were analyzed in detail. The effects of shell coating on the fluorescence lifetime, thermal stability and energy level transition are discussed. On this basis, the composite film material was constructed by combining the shell coating strategy and the plasma resonance interaction strategy, which further improved the upconversion efficiency. In addition, by combining performance optimized upconversion particles with information coding, we explored its potential as an anti-counterfeiting material.

An upconversion fluorescent and colorimetric dual-mode optical probe for triazophos pesticides

A dual-mode optical probe for organophosphorus pesticides triazophos (TRP) was developed on the basis of internal filter effect (IFE) between upconversion nanoparticles NaYF4: Yb/Er @NaYF4@SiO2 (UCNPs) and gold nanoparticles (AuNPs) in the presence of protamine (PRO) and Trypsin (TRY). In this essay, AuNPs can quench significantly the fluorescence intensity of UCNPs at 550 nm with 980 nm excitation. PRO is a cationic protein that binds AuNPs effectively and aggregates AuNPs due to electrostatic attraction. The aggregation of AuNPs made the solution blue and the fluorescence intensity of UCNPs at 550 nm was recovered correspondingly. Furthermore, TRY could hydrolyze PRO, and PRO will reduce AuNPs clustering due to the addition of TRY, inducing the solution to purple and quench the fluorescence of UCNPs again. After adding the TRP, the activity of TRY was inhibited, thereby preventing PRO hydrolysis and causing AuNPs to reaggregate. Reassembled AuNPs restored the fluorescence of UCNPs again. The inhibition efficiency of fluorescence and colorimetric has a good linear relationship with the logarithmic TRP concentration in the range of 0.03∼300 ng/mL, and the detection limits are 0.0052 and 0.0026 ng/mL, respectively. In addition, the recovery of TRP in real food samples with satisfactory results ranged from 96.02 to 104.30% and 95.63 to 105.64%, respectively.

Synthesis and surface modification of ultrasmall monodisperse NaYF4:Yb3+/Tm3+ upconversion nanoparticles

The emerging upconversion nanoparticles (UCNP) have gained substantial consideration in the field of bioanalytical as well as diagnostic applications. Therefore, great progress has been made in the synthesis and surface modification of luminescent UCNPs over the last two decades. In this paper, we have reported monodispersed and high luminescent upconversion nanoparticles NaYF4: 20%Yb3+, 2%Tm3+ have been synthesized using a solvothermal method, followed by a coating of the NaYF4 shell with a thin layer of SiO2 on the surface to afford the core-shell NaYF4:Yb3+, Tm3+@SiO2 nanoparticles (NP@SiO2). The prepared nanoparticles were of strong upconversion fluorescent emission intensity, hexagonal phase, and with an average size of about 8 ± 1 nm, which have been characterized by luminescence spectroscopy, powder X-ray diffraction (P-XRD), Dynamic light scattering (DLS), and Transmission electron microscopy (TEM). The results indicate that the NP@SiO2 can be used for the conjugation of fluorescent probes for various biomolecules and can find applications in cancer cell imaging and disease diagnosis.

Rapid determination of serum amyloid A using an upconversion luminescent lateral flow immunochromatographic strip.

The early diagnosis and real-time prognosis of cardiovascular diseases (CVDs) at the bedside are important. However, real-time detection of myocardial infarction involves the use of large-scale instrumentation and long test times. Herein, a simple, rapid and sensitive lateral flow immunochromatographic strip (LFIS) based on Yb/Er co-doped NaYF4 upconversion nanoparticles (UCNPs) was demonstrated for use in the detection of myocardial infarction. First, through heavy Yb/Er doping and an inert NaYF4 shell coating on the nanoparticles, the surface-related luminescence quenching effect of UCNPs was eliminated to enhance the upconversion luminescence. Second, through uniform coating of a SiO2 layer on the UCNPs, the biological affinity was improved to couple UCNPs and antibody proteins. Finally, through modification and activation with a specific antibody protein (serum amyloid A (SAA)), the UCNPs exhibited intense upconversion luminescence and high specificity when applied as a lateral flow immunochromatographic strip (LFIS). The developed UC-LFIS was highly sensitive (0.1 μg mL-1) and specific for detecting SAA in only 10 μL of serum. The UC-LFIS holds great potential for the early diagnosis and prognosis of CVDs.

Natural and Synthetic Polymer Scaffolds Comprising Upconversion Nanoparticles as a Bioimaging Platform for Tissue Engineering.

Modern biocompatible materials of both natural and synthetic origin, in combination with advanced techniques for their processing and functionalization, provide the basis for tissue engineering constructs (TECs) for the effective replacement of specific body defects and guided tissue regeneration. Here we describe TECs fabricated using electrospinning and 3D printing techniques on a base of synthetic (polylactic-co-glycolic acids, PLGA) and natural (collagen, COL, and hyaluronic acid, HA) polymers impregnated with core/shell β-NaYF4:Yb3+,Er3+/NaYF4 upconversion nanoparticles (UCNPs) for in vitro control of the tissue/scaffold interaction. Polymeric structures impregnated with core/shell β-NaYF4:Yb3+,Er3+/NaYF4 nanoparticles were visualized with high optical contrast using laser irradiation at 976 nm. We found that the photoluminescence spectra of impregnated scaffolds differ from the spectrum of free UCNPs that could be used to control the scaffold microenvironment, polymer biodegradation, and cargo release. We proved the absence of UCNP-impregnated scaffold cytotoxicity and demonstrated their high efficiency for cell attachment, proliferation, and colonization. We also modified the COL-based scaffold fabrication technology to increase their tensile strength and structural stability within the living body. The proposed approach is a technological platform for “smart scaffold” development and fabrication based on bioresorbable polymer structures impregnated with UCNPs, providing the desired photoluminescent, biochemical, and mechanical properties for intravital visualization and monitoring of their behavior and tissue/scaffold interaction in real time.

Dual‐Functional Nonmetallic Plasmonic Hybrids with Three‐Order Enhanced Upconversion Emission and Photothermal Bio‐Therapy

AbstractPlasmonic semiconductor nanoparticles (NPs) with wide‐range tailorable localized surface plasmon resonance (LSPR) hold exciting prospects on optical signal amplification. In this work, by precisely controlling oxygen vacancies around W atoms, plasmonic bismuth tungstate Bi2WO6 (BWO) nanosheets are constructed to enhance emission of Yb3+/Er3+ co‐doped NaYF4 upconversion nanoparticles (UCNPs). In the optimal conditions, the UCNPs/BWO‐2 hybrids exhibit over three‐order (1260‐fold) enhancement selectively on the 520 nm emission owing to the strong LSPR‐induced electrical field and photothermal effect. Moreover, it is found that the highly efficient emission of UCNPs/BWO‐2 allows it to act as a thermometer to monitor the real‐time local temperature with high absolute sensitivity of 5.8 × 10−3 K−1 in wide temperature range (up to 990 K). For proof‐of‐concept, the dual functions of plasmonic UCNPs/BWO‐2 hybrids on bioimaging and photothermal therapy for cancer cells are demonstrated that can be completely killed within 5 min under 980 nm irradiation. As far as it is known, this work reaches a new level on UCNPs emission enhancement by plasmonic semiconductor, exceeding most plasmonic metals.

Facile Synthesis of NaYF4:Yb Up-Conversion Nanoparticles Modified with Photosensitizer and Targeting Antibody for In Vitro Photodynamic Therapy of Hepatocellular Carcinoma.

Rare Earth up-conversion nanoparticles NaYF4:20%Yb,2%Er@PEI (UCNPs) were generated via a one-step hydrothermal technique at relatively reduced temperatures. Photosensitizer Ce6 and anti-EpCAM, a highly expressed monoclonal antibody in cancer stem cells of hepatocellular carcinoma, were linked to UCNP surfaces via the formation of amide linkage between carboxyl from Ce6 or anti-EpCAM and abundant amino from PEI, leading to the formation of Ps-Ce6 and anti-EpCAM-UCNPs-Ce6 nanoparticles. The synthesized nanoparticles characterized by XRD, TEM, and IR, and their zeta potential, ROS generation ability, Ce6 loading rate, and up-conversion fluorescence properties were investigated. It has been revealed that all the products were uniformly dispersed nanoparticles (25–32 nm), which crystallized primarily as hexagonal structures, and their up-conversion fluorescence spectra were similar to that of NaYF4:20%Yb,2%Er. The Ce6 loading rate in the anti-EpCAM-UCNPs-Ce6 nanoparticles was about 2.9%, thereby resulting in good ROS generation ability. For anti-EpCAM-UCNPs-Ce6, the biosafety, targeting effect, and PDT effect exposed under near-infrared (NIR) laser (980 nm) were evaluated using human liver cancer cells (BEL-7404). The results showed that it has good biocompatibility and biosafety as well as high targeting and PDT treatment efficiencies, which renders it a potential experimental material for the near-infrared PDT study.

Stability, dissolution, and cytotoxicity of NaYF4-upconversion nanoparticles with different coatings

Upconversion nanoparticles (UCNPs) have attracted considerable attention owing to their unique photophysical properties. Their utilization in biomedical applications depends on the understanding of their transformations under physiological conditions and their potential toxicity. In this study, NaYF4:Yb,Er UCNPs, widely used for luminescence and photophysical studies, were modified with a set of four different coordinatively bound surface ligands, i.e., citrate, alendronate (AA), ethylendiamine tetra(methylene phosphonate) (EDTMP), and poly(maleic anhydride-alt-1-octadecene) (PMAO), as well as silica coatings with two different thicknesses. Subsequently, the aging-induced release of fluoride ions in water and cell culture media and their cytotoxic profile to human keratinocytes were assessed in parallel to the cytotoxic evaluation of the ligands, sodium fluoride and the lanthanide ions. The cytotoxicity studies of UCNPs with different surface modifications demonstrated the good biocompatibility of EDTMP-UCNPs and PMAO-UCNPs, which is in line with the low amount of fluoride ions released from these samples. An efficient prevention of UCNP dissolution and release of cytotoxic ions, as well as low cytotoxicity was also observed for UCNPs with a sufficiently thick silica shell. Overall, our results provide new insights into the understanding of the contribution of surface chemistry to the stability, dissolution behavior, and cytotoxicity of UCNPs. Altogether, the results obtained are highly important for future applications of UCNPs in the life sciences and bioimaging studies.

Synthesis of photoactivable Pt(IV) prodrug loaded on NaYF4 based upconversion nanoparticles functionalized with 2-deoxy-D-glucose and its evaluation for targeted cancer therapy

Nano-formulation based on Tm, Yb doped NaYF4 upconversion nanoparticles (UCNPs) functionalized with 2-deoxy-D-glucose have been synthesized to load the photoactivable Pt(IV) prodrug, cis-[PtI2(NH3)2(OCOCH2CH2COOH)2]. The Pt(IV) prodrug has been synthesized by oxidation of cis-[PtI2(NH3)2] to [PtI2(OH)2(NH3)2] and its further treatment with succinic anhydride. It is loaded through ester bond formation between the carboxyl groups of Pt(IV) prodrug with hydroxyl groups of 2-deoxy-D-glucose (2-DG) coated on UCNPs. The cytotoxicity of formulation after exposing to 385 nm UV light and in absence of light is evaluated against MCF-7 cell lines by MTT assay. The results have revealed enhanced cytotoxicity of UV exposed nano-formulation. Additionally, the clonogenic assay has exhibited the decrease in plating efficiency as inferred from decreased surviving fraction around 20% only for UV activated formulation as compared to formulation in dark, as well as merely Pt(IV) prodrug. These results are indicative that more internalization of the formulation inside the cancer cells was achieved due to the presence of 2-DG rendering more efficiency to kill cancer cells.

Development of photocatalyst based on NaYF4: Yb, Tm@NaYF4: Yb, Ce/NH2-MIL-101 (Cr): Doping Ce3+ ions to promote the efficient energy transfer between core and shell

Utilization of the whole solar spectrum for the photocatalysis is still a challenge and interesting topic. A series of novel photocatalysts are fabricated by combination of core–shell upconversion nanoparticles NaYF4: Yb, Tm@NaYF4: Yb, Ce (Tm@Ce) with the NH2-MIL-101 (Cr) (NMC) (Tm@Ce/NMC). Tm@Ce/NMC displays the high stability, wide photoresponsive range from UV–Vis to NIR, and excellent photocatalytic activity for decomposition of RhB. With the optimal doping amount of Ce3+ ions and ratio between Tm@Ce and NMC, the degradation of RhB is improved by 1.13, 1.14, and 1.50 times as compared with NaYF4: Yb, Tm/NMC (Tm@NMC), under the simulated solar light, UV + Vis, and NIR, respectively. The enhanced photocatalytic activity of Tm@Ce/NMC is mainly attributed to the efficient energy transfer between core and shell by the doping Ce3+ ions along with the distinct charge separation and suppressed recombination. By the controlled synthesis, the NaYF4: Yb, Tm (YT) nanoparticle is developed with the similar size as the Tm@Ce to further testify the effect of doping Ce3+ ions and exclude the influence of the increased size. The photocatalytic activity of YT/NMC is the less than that of Tm@Ce/NMC, which is almost the same with that of Tm/NMC. It suggests that to merely increase the size of upconversion nanoparticles is not the judicious choice for enhancement of the photocatalytic activity. On the basis of the trapping experiments and other spectra properties, the possible photocatalytic mechanism is conjectured, which is helpful to refine the structure design with the ultimate aim to get the robust photocatalyst.

High Color-Purity Red, Green, and Blue-Emissive Core-Shell Upconversion Nanoparticles Using Ternary Near-Infrared Quadrature Excitations.

Development of multicolor-emitting upconversion nanoparticles (UCNPs) is of significant importance for applications in optical encoding, anti-counterfeiting, display, and bioimaging. However, realizing the orthogonal three-primary color (TPC) upconversion luminescence in a single nanoparticle remains a huge challenge. Herein, we have rationally designed core-multishell-structured NaYF4 UCNPs through regulating the dopant concentration, composition of luminescent layers, and shell position and thickness, which are capable of emitting red, green, and blue luminescence with high color purity in response to ternary near-infrared quadrature excitations (1560/808/980 nm). Moreover, their high color purity is well retained with varying excitation power densities. This orthogonal TPC emissions property of such UCNPs endows them with great promise in the field of security. As a proof-of-concept, we have demonstrated the feasibility of combining such UCNPs with MnO2 nanosheets for information encryption and decryption. This work not only offers a new way to achieve TPC upconversion luminescence at a single nanoparticle level but also broadens the scope of application for security protection.

Development of a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran by magnetic separation.

The contents of both pesticide residues and dextran are important parameters for evaluating the quality of sugarcane. In this study, a multicolor upconversion fluorescence immunoassay for the simultaneous detection of thiamethoxam and dextran was established on the basis of magnetic separation. Antigens of thiamethoxam and dextran were coupled to magnetic nanoparticles as the separation elements. Monoclonal antibodies of thiamethoxam (6C7D12) and dextran (3C6F7) were conjugated with the upconversion nanoparticles of NaYF4:Yb,Er with an emission wavelength at 544 nm and NaYF4:Yb,Tm with an emission wavelength at 477 nm to prepare the signaling elements, respectively. Due to the difference in the emission wavelength, the signaling elements bound on the separation elements could be detected simultaneously after separation by an external magnetic field. After optimization, the half-maximal inhibitory concentration (IC50) values of the immunoassay for thiamethoxam and dextran were 0.46 and 49.33 ng mL−1, respectively. The assay showed no cross-reactivity with the analogs of thiamethoxam and dextran except for clothianidin (8.7%). The average recoveries of thiamethoxam and dextran in sugarcane juice were 82.9–93.3% and 87.5–97.2%, respectively. The results indicated that the immunoassay could meet the requirements for the simultaneous quantitative detection of thiamethoxam and dextran.

Upconversion nanoparticles extending the spectral sensitivity of silicon photodetectors to λ = 1.5 μm

The telecommunication wavelength of λ = 1.5 μm has been playing an important role in various fields. In particular, performing photodetection at this wavelength is challenging, demanding more performance stability and lower manufacturing cost. In this work,upconversion nanoparticle (UCNP)/Si hybrid photodetectors (hybrid PDs) are presented, made by integrating solution-processed Er3+-doped NaYF4 upconversion nanoparticles (UCNPs) onto a silicon photodetector. After optimization, we demonstrated that a layer of UCNPs can well lead to an effective spectral sensitivity extension without sacrificing the photodetection performance of the Si photodetector in the visible and near-infrared (near-IR) spectrum. Under λ = 1.5 μm illumination, the hybrid UCNPs/Si-PD exhibits a room-temperature detectivity of 6.15 × 1012 Jones and a response speed of 0.4 ms. These UCNPs/Si-PDs represent a promising hybrid strategy in the quest for low-cost and broadband photodetection that is sensitive in the spectrum from visible light down to the short-wave infrared.

Ratiometric upconversion luminescence nanoprobes for quick sensing of Hg2+ and cells imaging

Rare earth upconversion nanomaterials have the advantages of near-infrared region excitation, almost zero interference background, large anti-Stokes shifts without broad emission peaks, which can overcome parts of the defects of organic fluorescent probes. In this work, core-shell rare earth upconversion nanoparticles NaYF4:Yb,Tm:20 %Yb,0.35 %Tm@NaYF4 (UCNPs) were synthesized, and then water-soluble nanoparticles DMSA-UCNPs and PAA-UCNPs were subsequently fabricated. Meanwhile a naphthalimide-based colormetric Hg2+-probe was synthesized, and assembled with DMSA-UCNPs and PAA-UCNPs to give composite nanoprobes A-DMSA-UCNPs and A-PAA-UCNPs toward mercury ions. Both nanoprobes use the upconversion luminescence ratio at 451 nm and 361 nm (UCL451/UCL361) as the detection signal, and can quickly respond to Hg2+ ions within 1–2 min. The detection limits of A-DMSA-UCNPs and A-PAA-UCNPs were calculated to be 2.47 μmol/L and 8.15 μmol/L respectively. A-DMSA-UCNPs and A-PAA-UCNPs both could be employed as ratiometric nanoprobes for Hg2+ imaging in living cell and lysosomal localization.

Local Overheating of Biotissue Labeled With Upconversion Nanoparticles Under Yb3+ Resonance Excitation.

Local overheating of biotissue is a critical step for biomedical applications, such as photothermal therapy, enhancement of vascular permeability, remote control of drug release, and so on. Overheating of biological tissue when exposed to light is usually realized by utilizing the materials with a high-absorption cross section (gold, silica, carbon nanoparticles, etc.). Here, we demonstrate core/shell NaYF4:Yb3+, Tm3+/NaYF4 upconversion nanoparticles (UCNPs) commonly used for bioimaging as promising near-infrared (NIR) absorbers for local overheating of biotissue. We assume that achievable temperature of tissue labeled with nanoparticles is high enough because of Yb3+ resonance absorption of NIR radiation, whereas the use of auxiliary light-absorbing materials or shells is optional for photothermal therapy. For this purpose, a computational model of tissue heating based on the energy balance equations was developed and verified with the experimentally obtained thermal-graphic maps of a mouse in response to the 975-nm laser irradiation. Labeling of biotissue with UCNPs was found to increase the local temperature up to 2°C compared to that of the non-labeled area under the laser intensity lower than 1 W/cm2. The cellular response to the UCNP-initiated hyperthermia at subcritical ablation temperatures (lower than 42°C) was demonstrated by measuring the heat shock protein overexpression. This indicates that the absorption cross section of Yb3+ in UCNPs is relatively large, and microscopic temperature of nanoparticles exceeds the integral tissue temperature. In summary, a new approach based on the use of UCNP without any additional NIR absorbers was used to demonstrate a simple approach in the development of photoluminescent probes for simultaneous bioimaging and local hyperthermia.

Preparation of spherical upconversion nanoparticles NaYF4:Yb,Er by laser ablation in liquid and optical properties

Spherical upconversion nanoparticles, NaYF4:Er,Yb, were successfully prepared by laser ablation in liquid. The number of photons related to luminescence from the nanoparticles was 2. Micrometer-sized raw materials were irradiated with a nanosecond-pulsed laser (Nd:YAG, SHG) to prepare nanoparticles. The particle size of prepared spherical nanoparticles was a few hundred nanometers. The composition of nanoparticles was the same as that of the raw material even by using the high-temperature process of laser ablation in liquid. Fine nanoparticles prepared at high laser fluence by a focused laser beam would be melted at low laser fluence and cooled to prepare the spherical nanoparticles. The amount of spherical nanoparticles was increased by using the unfocused laser beam. This phenomenon supported the formation mechanism of spherical nanoparticles.

Temperature-dependent Förster resonance energy transfer from upconversion nanoparticles to quantum dots.

The Förster resonance energy transfer (FRET) from the β-NaYF4:Yb3+, Er3+/NaYF4 upconversion nanoparticles (UCNPs) to ZnCdSe/ZnS quantum dots (QDs) as a function of temperature (77-427 K) is demonstrated. With an increasing of temperature, both the intensity and peak position of QDs emission variated, which is attributed to the combining of the FRET and thermal quenching effect. By analyzing the dependence of the photoluminescence (PL) spectra on temperature, the UCNP + QD sample can be considered as dual thermal probes with high sensitivity based on either the UCL or the spectral shift of QD emission under 980 nm excitation. The lifetime of the UCNP and UCNP + QD samples are collected to investigate the dynamics of the FRET at various temperatures, showing a decrease and then an increase of the FRET efficiency from UCNPs to QDs with temperature from 77 to 427 K. This result is mainly attributed to the variation of the Förster distance R0 with the increasing of temperature. The work will be significant to detect the nanoscale interaction and it can be widely applied in biomedical, sensing and imaging.

Near-Infrared Light-Induced Sequential Shape Recovery and Separation of Assembled Temperature Memory Polymer Microparticles.

Light-induced, shape-changing polymeric microparticles have many applications. Here, the near-infrared (NIR)-light-triggered sequential recovery and separation of assembled large and small polymer microparticles using cross-linked blends of poly(ethylene-vinyl acetate) and trans-polyisoprene as temperature memory polymers as well as two NaYF4 based up-conversion nanoparticles (UCPs) to provide luminescent and photothermal effects are reported. Under irradiation of NIR light with a low light power density, small particles assembled onto the compressed large one recover first due to the low switching temperature (Tsw ) arising from the temperature-memory effect. The small particles can separate from the underlying large particle in flowing aqueous media. The recovery of the large particle occurs at a high power density. Two UCPs of NaYF4 : 20Yb, 0.2Tm, 5Gd and NaYF4 : 18Yb, 2Er, 5Gd facilitate the detection of small and large microparticles via providing blue and green light emissions, respectively. This work can expand the applications of light-induced shape-changing polymer microparticles in the biomedical field, controlled catalysis, microfluidic devices, and so on.

Near-Infrared- and Magnetic-Field-Responsive NaYF4:Er3+/Yb3+@SiO2@AuNP@Fe3O4 Nanocomposites for Hyperthermia Applications Induced by Fluorescence Resonance Energy Transfer and Surface Plasmon Absorption

Monodispersed upconversion nanoparticles NaYF4:Er3+/Yb3+ (UCNPs) have been synthesized via the thermolysis method. Forster or fluorescence resonance energy transfer (FRET) dynamics from NaYF4:Er3+/...