Energy Back Transfer Process Research Articles

Yb3+/Ho3+ doped Ba3Y2B4O12 phosphors: Upconversion luminescence and temperature sensing properties

Optical thermometry achieved by luminescent materials with good stability and high sensitivity has attracted much attention. In this article, Ba3Y2B4O12, a borate with good chemical stability and high laser threshold was chosen to be host material for preparing a series of Ba3Y2-x-yYbxHoyB4O12 (BYBO:xYb3+/yHo3+; 0.01 ≤ x ≤ 0.35, 0.005 ≤ y ≤ 0.035) upconversion phosphors by a facile solid-state method. Under 980 nm excitation, phosphors show strong 551 nm green emission, weak 668 nm red emission, and 755 nm near-infrared emission, while bright greenlight can be observed by naked eye. When x = 0.15, y = 0.01, luminescent intensity obtains the maximum value. At higher doping concentration, the reduction of cell parameters caused by doping can accelerate the decrease of distance between dopants, so that the energy back transfer process is more likely to occur, weakening the green emission. The intensified non-radiative relaxation results in an increased red emission proportion at higher temperature. According to this rule, the temperature sensing properties based on the fluorescence intensity ratio I668/I551 and I688/I755 are studied. The maximum relative sensitivity (SR) reaches 1.53 % K−1 at 478 K, which is higher than most of reported materials. It shows that BYBO:Yb3+/Ho3+ has application potential in temperature sensing.

Effect of Yb3+ concentration on the upconversion emission properties of sub 10 nm RbY2F7:Yb, Er nanoparticles.

Upconversion nanoparticles (UCNPs) are a fascinating group of luminescent materials known for their ability to convert low-energy photons to high-energy photons. Many inorganic UCNPs have been studied to understand the underlying mechanism of upconversion phenomena, out of which alkali rare-earth fluorides (AREFs) such as NaREF4, LiREF4 and KREF4 were found to exhibit high upconversion efficiencies. This work investigates a similar AREF upconversion nanoparticle viz RbY2F7:Yb, Er. This UCNP system was synthesised by a modified thermal decomposition method by varying the Yb concentration from 20% to 98%. Structural analysis using XRD revealed that all the synthesised samples were found to be formed in the orthorhombic phase irrespective of the increasing Yb concentration. The thermal decomposition method greatly aided in the reduction of particle size. HRTEM analysis revealed that the as-synthesised UCNPs have a spherical morphology with an average particle size of 7.9 ± 0.2 nm. The upconversion emission studies taken by exciting the samples with a 975 nm laser show three distinct peaks at 527, 542 and 656 nm. The experimental results indicate that the increased Yb3+ concentration improves the red to green intensity ratio by supporting the 4F9/2 → 4I15/2 transition of Er3+ through the energy back transfer process between Er3+ and Yb3+. Notably, there is a reduction in the overall emission intensity with increasing Yb3+ concentration. Furthermore, the decay lifetime studies show a decreasing trend at 542 nm and 656 nm emission lines with an increase in the Yb concentration, which is because of the concentration quenching effect of the increasing Yb concentration.

The pathways of electronic excitation back energy transfer processes (BET) in novel Eu3+ heterocyclic 1,3-diketonates bearing a perfluorinated moiety

A series of novel brightly emitting Eu3+ coordination compounds with 1,3-diketones bearing a thiophene moiety and a linear CnF2n+1 chain (n = 1–8) were synthesized and fully characterized. The dependence of back energy transfer (BET) processes on the fluorinated chain length of the ligand environment was investigated in detail. The rates of radiative, non-radiative, and BET processes were estimated by a complete set of spectroscopic methods, including temperature stimulated luminescence measurements. It was demonstrated that fluorination provided a remarkable increase in the photoluminescence quantum yield up to 58% along with an increase in sensitization efficiency from 45 to 86%. It was explained by the reduction of non-radiative relaxation on molecular oscillators. The probability of the BET process has a trend to decrease from 500 to 100 s−1 upon an extension of the diketone fluorinated chain. Moreover, the back energy transfer process occurs from the resonant level of Eu3+ ion to ligand triplet state T1 through activation energy barrier ΔEA between potential energy surfaces of T1 and 5D0 states. It was found that extension of the fluorinated chain in ligand alter the activation energy and frequency factor of BET. The influence of the both parameters on BET was studied. The results obtained give a fundamental basis for further rational design of highly efficient luminescent compounds of Eu3+ ions.

Locking Energy Transfer of Rare Earth Ions via an “Electron Jam” Caused by Vertical Photocarrier Separation of a Layered Semiconductor

Energy transfer (ET) of trivalent rare earth (RE)-doped inorganic crystals has been investigated comprehensively from theory to technology; however, the influence of photocarrier transmission has been considered impossible, as the 4f electrons of RE ions are shielded well from outer electrons. Here, on the basis of an anisotropic Bi3O4Cl layered semiconductor, we report for the first time the ET phenomenon of an Er3+–Yb3+ codoped system locked by photocarrier separation. When the photocarrier of the layered host is separated efficiently under a vertical spontaneous interelectric field, the ET and energy-back-transfer (EBT) between Er3+ and Yb3+ ions can be inhibited completely; otherwise, they can occur as usual. Consequently, the Yb3+ ion dopant mainly acts as a quencher for 980 nm-excited visible upconversion (UC) and infrared emission of Er3+ ions, and the cross-relaxation between Er3+ and Yb3+ ions via EBT is inhibited simultaneously. We show that the separated photoholes on the surface can suppress the recombination of excited electrons of Er3+ ions to the ground level, leading to a special “electron jam” on intermediate levels, which prevents the acceptance of excited electrons further via either the ET or EBT process. The result of our current work greatly enhances the understanding of ET behavior of RE ions and the material structure of RE-doped materials.

Tuning size and up-conversion luminescence of CeO2:Yb3+/Er3+ nanoparticles through lanthanide doping

Particle size is a critical parameter in up-conversion luminescence tuning and application research. In this study, CeO2:Yb3+/Er3+ nanospheres were synthesized via coprecipitation. The average size of these nanospheres gradually decreased as the Yb3+ doping concentration increased, which might be attributed to the influence of Yb3+ doping on the growth rate of nanospheres by surface charge repulsion. Upon exciting these nanospheres using a 980-nm laser, the corresponding up-conversion red-green emission intensity ratio gradually increased as the Yb3+ doping concentration increased, which might be ascribed to two reasons: the strengthened 4S3/2 → 4F9/2 nonradiative relaxation process and the enhanced Er3+ → Yb3+ energy back-transfer process. To assess the influence of the nonradiative relaxation process on the up-conversion emission red-green ratios, the down-conversion emission spectra and decay curves of CeO2:x%Yb3+/2%Er3+ nanospheres that were excited by a 520 nm laser were investigated. To validate how the particle size affects the up-conversion emission, CeO2:x%Lu3+/2%Yb3+/2%Er3+ nanospheres of various sizes were synthesized by substituting optically active Yb3+ using optically inert Lu3+. The corresponding up-conversion emission spectra and decay curves were investigated. The experimental results enhanced our understanding of how lanthanide doping affects the up-conversion luminescence tuning of Er3+, offering great potential to regulate the morphology and optical properties of the up-conversion luminescence nanoparticles.

Deep red upconversion photoluminescence in Er3+‐doped Yb3Ga5O12 nanocrystalline garnet

AbstractThe nanocrystalline single‐phase Er3+‐doped Yb3Ga5O12 garnets have been prepared by the sol‐gel combustion technique with a crystallite size of ≈30 nm. The presence of Yb3+ in garnet hosts allows their efficient excitation at the ≈977 nm wavelength. The Er3+ doping of Yb3Ga5O12 garnet host results in deep red Er3+: 4F9/2 → 4I15/2 upconversion photoluminescence (UCPL) emission. The dominance of the red UCPL emission over the green Er3+: 4F7/2/2H11/2/4S3/2 → 4I15/2 component was investigated using the measurement of the steady‐state and time‐dependent Er3+ and Yb3+ emission spectra in combination with the power‐dependent UCPL emission intensity. The proposed upconversion mechanism is discussed in terms of the Er3+ → Yb3+ energy back transfer process as well as Yb3+(Er3+) → Er3+ energy transfer and Er3+ ↔ Er3+ cross‐relaxation processes. The studied Er3+‐doped Yb3Ga5O12 garnet may be utilized as a red upconversion emitting phosphor.

Enhanced ultraviolet upconversion emission in Ho3+/Yb3+-codoped NaYF4 microcrystals induced by tridoping with Gd3+ ions

NaY(0.78-x)GdxHo0.02Yb0.2F4 (x = 0, 0.2, 0.4) microcrystals are synthesized by hydrothermal process. Ultraviolet upconversion emissions centered at 340 and 360 nm in Ho3+/Yb3+/NaYF4 microcrystals, which are stimulated by 976 nm lasers, can be enhanced by tridoping with Gd3+ ions. The ultraviolet upconversion radiations are enhanced more than fourfold for Gd3+ ions concentrations of 20 mol%. The X-ray diffraction (XRD) data mean that the enhancement is not come from expanding structural. Excitation and down emission spectra and decay lifetimes results demonstrate that the enhancement due to an energy back transfer process (PJ6(Gd3+)→(F5, F3, G5)2 (Ho3+)). The UV UC mechanisms are supported by decay lifetime and pump power dependence.

Effects of Er3+/Yb3+ Doping Concentration on the Crystal Structure and Luminescence Properties of Gd1.985Lu0.015O2S Up-Conversion Phosphors

A series of Er3+ and Yb3+ co doped Gd1.985Lu0.015O2S phosphors were prepared by the high-temperature solid state method. The crystal structure and luminescence characteristics of a series of samples were analyzed by X-ray diffraction (XRD), up-conversion luminescence spectra and decay curves. Under the excitation of 980 nm laser, the sample exhibited two green and one red emission, which belonged to the transitions of Er3+ ion 2H11/22 → 4I15/2,4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. In addition, the energy transfer process between Er3+ and Yb3+ ions is described according to the energy level diagram. When the concentration of Er3+ and Yb3+ is too high, the concentration quenching effect occurs, which increases the reverse energy transfer from Er3+ to Yb3+ and reduces the luminescent brightness. A series of decay curves show that the strain fluorescence lifetimes at 548 nm and 670 nm decrease with the increase of Er3+ and Yb3+ concentration, which is due to the increase of Er3+ cross relaxation process and the back energy transfer process between the two ions. Subsequently, the introduction of Lu3+ ions was found to be beneficial to improve the temperature stability of the material by temperature dependent spectroscopy (300K–500K). This work provides useful ideas for the development of infrared detection materials with better temperature stability.

Super Bright Red Upconversion in NaErF4:0.5%Tm@NaYF4:20%Yb Nanoparticles for Anti-counterfeit and Bioimaging Applications.

Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600-900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF4:0.5%Tm@NaYF4:20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF4:0.5%Tm@NaYF4 (core@inactive shell). Here, an Er3+-enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb3+ ions efficiently transfers the energy to the Er3+-enriched core, which suppresses the nonradiative channel rate, and Tm3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.

Enhancing upconversion emission of Er3+ in single β-NaYF4 microrod through constructing different inert and active shells with doping Yb3+ ions

The construction of core-shell structure helps in enhancing upconversion luminescence in lanthanide-doped micro/nanomaterials. This study aimed to synthesize a series of NaYF4 and NaErF4 core-shell microrods based on epitaxial growth technology so as to enhance the upconversion emission. The upconversion luminescence properties of single NaYF4:Yb3+/Er3+ and NaErF4 microrods with different core-shell structures were carefully studied using a confocal microscope spectroscopy test system under 980-nm near-infrared excitation. The upconversion emission intensity and red-to-green emission intensity ratio of Er3+ ions were remarkably enhanced in different single microrods by building different inert and active core-shell structures. The higher red-to-green ratio was mainly due to the cross-relaxation between Er3+ ions and the energy back-transfer process from Er3+ to Yb3+ ions, which were explained on the basis of spectral characteristics and rate equations. These tunable NaYF4 and NaErF4 core-shell microrods had the potential to be applied to displays, micro-lasers, and anti-counterfeiting.

Flame-made Y2O3:Yb3+/Er3+ upconversion nanoparticles: Mass production synthesis, multicolor tuning and thermal sensing studies

Developing a rapid and continuous synthesis method for scalable production of upconversion nanoparticles (UCNPs) plays an important role in the applications of advanced color display, high-resolution biomedical imaging and precise optical thermometry. Here, for the first time, we report the multicolor tunable upconversion luminescence (UCL) in Y2O3:Yb3+/Er3+ (x/1 mol%) UCNPs with the average size of ∼14 nm, which were successfully fabricated by liquid-fed flame aerosol synthesis with a high production rate of ∼40 g h−1. Under the excitation of 980 nm continuous-wave (CW) laser, the UCL color can be efficiently modulated from green to red and the red-to-green (R/G) UCL intensity ratio is enhanced dramatically as the doping concentration of Yb3+ ions increases from 1 to 15 mol%. The UCL color manipulation can be ascribed to the cross-relaxation (CR) and the energy back transfer (EBT) processes between Yb3+ and Er3+ ions, and it was proved by investigating the dependence of UCL on the pump power and the decay lifetimes of 4S3/2 and 4F9/2 states. Moreover, the coefficients of CR and EBT processes were also calculated by a rate equation model, and the results suggest that they are efficient in Y2O3 host. In addition, the optical thermal sensing performance was also evaluated by analyzing fluorescence intensity ratio (FIR) of the thermally coupled levels (2H11/2, 4S3/2) of Er3+ ions in Y2O3:Yb3+/Er3+ (1/1 mol%) UCNPs, achieving an excellent thermal sensitivity of 0.0196 K−1 at 543 K.

An Europium (III) Luminophore with Pressure-Sensing Units: Effective Back Energy Transfer in Coordination Polymers with Hexadentate Porous Stable Networks.

A luminescent EuIII coordination polymer with O2 -sensing units under air, EuIII -hcpt (hcpt: 2,3,6,7,10,11-hexakis(4-carboxy-phenyl)triphenylene), is reported. The hexadentate carboxylic acids in hcpt ligands play an important role in the formation of tight-packed three-dimensional networks in EuIII -hcpt, giving hyper thermo-stable structures (decomposition temperature=420 °C). The three-dimensional porous network promotes bright luminescence (4f-4f emission quantum yield=70 %). The emission lifetime of EuIII -hcpt under vacuum (0.86 ms) was twice as large as that under O2 (0.48 ms, 1 atom:101.3 kPa). The Arrhenius analysis of the emission decay profile indicates that the back energy transfer (BEnT) from the emitting level of the europium(III) ion to the excited T1 state of the hcpt ligand should be activated at room temperature. The gradual decrease of emission lifetime is caused by the BEnT process in EuIII -hcpt. Finally, an advanced pressure-sensitive luminophore is demonstrated.

Small-sized red-emitting core/shell/shell nanoparticles through an efficient energy back transfer process

From the existing Er3+-based upconversion (UC) research, we can't judge whether the 980 nm near-infrared (NIR) emission photons from Er3+ in core or the 980 nm NIR excitation photons from laser were captured by Yb3+ in active shell, due to 980 nm excitation was the only excitationmode in the previous reports. In this work, the systematic research of small-sized (about 20 nm) NaErF4:0.5%Tm@NaYbF4@NaYF4 core/shell/shell nanoparticles with intense red UC luminescence under 808/980/1532 nm excitations is presented for the first time. We confirm that 980 nm NIR emissionphotons from Er3+ in core which would inevitably transfer to the external space, must be captured by Yb3+ in active shell. The coating of NaYbF4 active shell can maximize the capture of 980 nm NIR emissionphotons from Er3+ in core. Under theprotection of NaYF4 inert outer shell, the efficient energy back transfer from NaYbF4 active shell to Er3+ in core may induce the 4I15/2 → 4I11/2 and 4I13/2 → 4F9/2 transitions of Er3+, leading to the bright red UC luminescence with high purity under 808/980/1532 nm excitations. The small-sized red-emitting core/shell/shell nanoparticles under multiple excitations exhibit huge advantages in bioimaging and solar energy conversion.

Tunable upconversion luminescence and optical temperature sensing based on non-thermal coupled levels of Lu3NbO7:Yb3+/Ho3+ phosphors

The color-tunable upconversion (UC) emission and optical temperature sensing based on non-thermal coupled levels (NTCL) were observed from the Yb3+/Ho3+ codoped Lu3NbO7 phosphors synthesized by the solid-state method. The phosphors are capable of generating color tunable UC luminescence from green (yellow) to yellow (green) with the increase of the Yb3+ (Ho3+) concentration. The tunable emission is due to the different energy back transfer processes from Ho3+ to Yb3+. The temperature sensing performances are investigated in the temperature range of 293–573 K based on NTCL by using fluorescence intensity ratio technology. The maximum absolute sensitivities are 0.37%K−1, 0.94%K−1, 0.27%K−1 at 298 K, which are based on three pairs NTCL of (5F4/5S2→5I8)/(5F5→5I8), (5F5→5I8)/(5F4/5S2→5I7) and (5F4/5S2→5I8)/(5F4/5S2→5I7) of Ho3+, respectively. The above results suggest that the as-prepared Lu3NbO7:Yb3+/Ho3+ phosphors have great potential for the application prospects of upconverter, color tunable device and optical temperature sensor.

Simultaneous phase and morphology control of Ba2YbF7: Er3+ upconversion nanocrystals through La3+ doping

Lanthanide doped upconversion nanocrystals are widely applied in biological imaging, photonics, photovoltaics and therapeutics. Highly monodispersed and uniform products with controllable optical modulation of upconversion fluorescence really matters their promising applications. Here, Er3+ doped Ba2YbF7 nanocrystals with phase transformation, controllable morphology and tunable upconversion emission color is investigated via varying the concentration of La3+. Accompanied with tetragonal Ba2YbF7 transformed to be cubic phase, nanocubes appear instead of nanorods, and a distinct upconversion color changing from yellow to green is obtained. Crystal structure management of Ba2YbF7 contributing to a suppressive back energy transfer process, which facilitates a controllable upconversion color in monodispersed nanocrystals with a uniform morphology, is demonstrated.

Ligand-Assisted Back Energy Transfer in Luminescent TbIII Complexes for Thermosensing Properties.

A luminescent TbIII complex with a hexafluoroacetylacetone (hfa) ligand shows a characteristic back energy transfer (BEnT), which leads to high temperature sensitivity and potential application as a thermosensitive paint. Ligand-assisted BEnT was observed when a phosphine oxide ligand was introduced into Tb(hfa)3 complex, which was shown to affect the activation energy (ΔEa ) and frequency factor (A) in the BEnT process between TbIII ion and hfa ligands. According to temperature-dependent emission-lifetime measurements of mononuclear Tb(hfa)3 complexes with monodentate phosphine oxides and polynuclear Tb(hfa)3 complexes with bidentate phosphine oxides, the ΔEa and A values of polynuclear TbIII complexes were smaller than those of mononuclear TbIII complexes. Phosphorescence spectra and lifetimes of each Gd(hfa)3 complex revealed that excited states of hfa ligands in TbIII complexes differed from those of the polynuclear TbIII complexes and mononuclear TbIII complexes. The differences in the ΔEa and A values between polynuclear and mononuclear TbIII complexes were caused by the formation of different excited states, such as delocalization of the excited state in the polynuclear TbIII complexes and localization of excited states in the mononuclear TbIII complexes. In particular, small ΔEa and A values of polynuclear TbIII complexes provided high, effective activation of the BEnT at low temperature, which resulted in high-sensitive temperature-dependent phosphor materials over a wide temperature range.

A luminescent Lanthanide-free MOF nanohybrid for highly sensitive ratiometric temperature sensing in physiological range

Luminescent MOF materials with tunable emissions and energy/charge transfer processes have been extensively explored as ratiometric temperature sensors. However, most of the ratiometric MOF thermometers reported thus far are based on the MOFs containing photoactive lanthanides, which are potentially facing cost issue and serious supply shortage. Here, we present a ratiometric luminescent thermometer based on a dual-emitting lanthanide-free MOF hybrid, which is developed by encapsulation of a fluorescent dye into a robust nanocrystalline zirconium-based MOF through a one-pot synthesis approach. The structure and morphology of the hybrid product was characterized by Powder X-ray diffraction (PXRD), N2 adsorption-desorption measurement and Scanning electron microscopy (SEM). The pore confinement effect well isolates the guest dye molecules and therefore suppresses the nonradiative energy transfer process between dye molecules. The incorporated dye emission is mainly sensitized by the organic linkers within MOF through fluorescence resonance energy transfer. The ratiometric luminescence of the MOF hybrid shows a significant response to temperature due to the thermal-related back energy transfer process from dye molecules and organic linkers, thus can be exploited for self-calibrated temperature sensing. The maximum thermometric sensitivity is 1.19% °C−1 in the physiological temperature range, which is among the highest for the ratiomtric MOF thermometers that operating in 25–45°C. The temperature resolution is better than 0.1°C over the entire operative range (20–60°C). By integrating the advantages of excellent stability, nanoscale nature, and high sensitivity and precision in the physiological temperature range, this dye@MOF hybrid might have potential application in biomedical diagnosis. What’ more, this work has expanded the possibility of non-lanthanide luminescent MOF materials for the development of ratiometric temperature sensors.

Highly efficient multi-colour upconversion emission of Yb3+/Er3+, Ho3+ codoped single LiYF4 octahedral microparticle

In this work, Yb3+/Er3+, Ho3+ codoped tetragonal-phase LiYF4 octahedral microparticles have been successfully synthesized through a facile hydrothermal method. Here, we implemented a confocal microscopy setup to manipulate and study the optical properties of a single LiYF4 microparticle under a focused NIR 980nm excitation. The strong multi-colour upconversion emission intensity with beautiful luminescent patterns have been clearly observed. And output colours (the different ratio of red-to-green emission intensity) of single LiYF4: Yb3+/Er3+, Ho3+ microparticles have been anticipated to be adjusted by controlling Yb3+ doping concentrations. The results show that the different ratio of red-to-green emission intensity of Er3+ and Ho3+ in single LiYF4 microparticle, which is due to the cross-relaxation processes and energy back transfer processes between Yb3+ ions and Er3+ or Ho3+ leading to different population densities of intermediate energy levels. The upconversion emission mechanisms and the influence of Yb3+ concentrations on upconversion emission properties of Er3+ and Ho3+ ions are also discussed according to the emission spectra and rate equations.

Investigation of NIR-to-red upconversion luminescence mechanism in Y2O3:Er3+,Yb3+ and the effect of co-doping Zn in the matrix

We studied composite ZnO:Y2O3 matrix for upconversion luminophore pair Er:Yb using near IR light excitation. Uni-phase crystalline nanoparticles were produced up to a 4% co-doped ZnO in Y2O3. In ZnO:Y2O3 co-host matrix, Er(2%):Yb(10%) pair emits strong red luminescence. Doping 4% ZnO into the matrix enhances the luminescence by ~ 2.5 times. The mechanisms for the predominant red emission in the presence and absence of Zn ions were studied. An energy back transfer (EBT) process from Er to Yb is the main pathway for the intense red emission under NIR excitation although other mechanisms, e.g. Er-Er cross relaxation (CR), may also contribute to the red emission. The Er-Yb EBT process brings the Er ion from the green emission state to the intermediate 4I13/2 state, which further absorbs a near IR photon and jumps to the red emission state. The introduction of ZnO into Y2O3 matrix does not interfere with this process significantly. Thus, the enhancement of luminescence is mainly caused by the breaking of the symmetry around Er3+ ions due to the Y-to-Zn substitution, which favors the f-f electric dipole transitions that are forbidden in centrosymmetric environment.

Luminescence spectroscopy and near-infrared to visible upconversion in Er3+ and Yb3+ codoped Sc2O3 nanoparticles

The Er3+ and Yb3+ co-doped Sc2O3 nanoparticles were prepared by co-precipitation method. The phase structure and up-conversion properties were investigated using XRD, FESEM and up-conversion spectra. The nanoparticles with the size of about 40nm emitted red and green light. Yb3+ ions are crucial to adjust the intensity proportion of red and green emission as a sensitizer. In Er3+, Yb3+ co-doping samples, the red emissions are much higher than green and the intensity ratio is up to 56.43, while the green to red intensity ratio is 11.21 with Er3+ single doping, which both show excellent mono-chromaticity. Strong red emissions are attributed to the cross-relaxation energy transfer and energy back-transfer processes. High Yb3+ ions concentrations induce the red up-conversion saturation, resulting in a near linear laser power dependence, and it can be illustrated based on steady-state rate equations.