States Of Er3 Research Articles

Defect level induced negative thermal quenching of β-Ba3LuAl2O7.5: Yb3+, Er3+ phosphor

Temperature-dependent behavior of phosphors has recently attracted significant research attention. This is due to the widespread applications of phosphors. Unfortunately, the thermal quenching effect in many phosphors greatly limits their performance at high temperatures. Herein, negative thermal quenching phosphor β-Ba3LuAl2O7.5: 0.3Yb3+, 0.03Er3+ is synthesized using the high-temperature solid-state method. X-ray Rietveld refinement and EPR results indicate the defect state of oxygen vacancy. Temperature-dependent upconversion luminescence spectra demonstrate that the green and red emission intensities increase with temperature to reach maximums at 398 K and 348 K respectively. Diffuse reflectance spectrum and downshifting luminescence spectrum prove that the defect state is near the 4F7/2 state of Er3+ ions. The defect state traps electrons at room temperature and releases them to populate the 4F7/2 state of Er3+ ion at elevated temperatures to cause the observed thermal enhancement of upconversion luminescence. This material's negative thermal quenching effect makes it a suitable candidate for applications in displays and anti-counterfeiting.

Phonon-mediated temperature dependence of Er3+ optical transitions in Er2O3

Characterization of the atomic level processes that determine optical transitions in emerging materials is critical to the development of new platforms for classical and quantum networking. Such understanding often emerges from studies of the temperature dependence of the transitions. We report measurements of the temperature dependent Er3+ photoluminescence in single crystal Er2O3 thin films epitaxially grown on Si(111) focused on transitions that involve the closely spaced Stark-split levels. Radiative intensities are compared to a model that includes relevant Stark-split states, single phonon-assisted excitations, and the well-established level population redistribution due to thermalization. This approach, applied to the individual Stark-split states and employing Er2O3 specific single-phonon-assisted excitations, gives good agreement with experiment. This model allows us to demonstrate the difference in the electron-phonon coupling of the 4S3/2 and 2H11/2 states of Er3+ in E2O3 and suggests that the temperature dependence of Er3+ emission intensity may vary significantly with small shifts in the wavelength (~0.1 nm) of the excitation source.

Near-Infrared Photoluminescence from Ytterbium- and Erbium-Codoped CsPbCl3 Perovskite Quantum Dots with Negative Thermal Quenching.

Near-infrared (NIR) luminescent phosphors hold promise for a wide range of applications, from bioimaging to light-emitting diodes (LEDs), but are typically confined to wavelengths <1300 nm and manifest substantial thermal quenching pervasive in luminescent materials. Here we observed the thermally enhanced NIR luminescence of Er3+ (1540 nm), a 2.5-fold enhancement with increasing temperature from 298 to 356 K, from Yb3+- and Er3+-codoped CsPbCl3 perovskite quantum dots (PQDs) (photoexcited at ∼365 nm). Mechanistic investigations revealed that thermally enhanced phenomena originated from combined effects of thermally stable cascade energy transfer (from a photoexcited exciton to a pair of Yb3+ and then to surrounding Er3+) and minimized quenching of surface-adsorbed water molecules on the 4I13/2 state of Er3+ induced by the temperature increase. Importantly, these PQDs enable producing phosphor-converted LEDs emitting at 1540 nm with inherited thermally enhanced properties, having implications for a wide range of photonic applications.

Ultralow pressure sensing and luminescence thermometry based on the emissions of Er3+/Yb3+ codoped Y2Mo4O15 phosphors.

Pressure and temperature are fundamental physical parameters, so their monitoring is crucial for various industrial and scientific purposes. For this reason, we developed a new optical sensor material that allows monitoring of both the physical parameters. The synthesized material exhibits upconversion (UC) emission of Er3+ in the red and green spectral regions under NIR (975 nm) laser irradiation. These UC emissions are strongly temperature-dependent, allowing multimode temperature sensing, either based on the luminescence intensity ratio between thermal-coupled energy levels (TCLs) or non-thermal-coupled energy levels (NTCLs) of Er3+ ions. Meanwhile, the luminescence lifetime of the 4S3/2 state of Er3+ ions was used as the third temperature-dependent spectroscopic parameter, enabling multi-parameter thermal sensing. Moreover, the observed enhancement of laser-induced heating of the sample under vacuum conditions allows for the conversion of the luminescent thermometer into a remote vacuum sensor. The pressure variations in the system are correlated with changes in the band intensity ratio (525/550 nm) of Er3+ TCLs, which are further applied for optical, contactless vacuum sensing. This is because of the light-to-heat conversion effect, which is greatly enhanced under vacuum conditions and manifests as a change in the intensity ratio of Er3+ bands (525/550 nm). The obtained results indicate that an Y2Mo4O15:Er3+/Yb3+ (YMO) phosphor has great application potential for the development of multi-functional and non-invasive optical sensors of pressure and temperature.

Enhanced 3.1µm mid-infrared emission from Er3+/Yb3+ co-doped tellurite glass pumped by 980nm laser diode

Yb3+ ions co-doping was attempted for the first time for sensitizing Er3+ ions and increasing the 3.1 µm fluorescence, originating from the transition from Er3+: 4S3/2 → 4F9/2. Under a 980 nm LD excitation, strong 3.1 µm fluorescence in the mid-infrared (MIR) region and the related energy level change process were investigated. An enhanced 3.1 µm emission was attained from the Er3+/Yb3+ co-doped tellurite glass with the increment in Yb2O3 content, which demonstrated that the Yb3+ ions may act as the sensitizer to the Er3+ ions, thereby providing an effective energy transport channel from the 2F5/2 state of Yb3+ ions to the 4S3/2 state of Er3+ions. Moreover, the measured emission band full width at half maximum reaches about 164 nm along with the maximum emission cross-section (2.88 × 10−21 cm2). The outcome of our work suggests that upon co-doping with Er3+/Yb3+, the tellurite glass may function as a prospective material for fabricating the matrix of 3.1 µm MIR lasers.

Downconversion mechanism in Er3+/Yb3+ codoped fluorotellurite glasses to enhance the efficiency of c-Si PV cells

Fluorotellurite glass codoped with erbium and ytterbium was elaborated through the melting-quenching route. Through the DSC and Raman measurements, the investigated glass samples presented high thermal stability and low phonon energy, respectively. By using the laser excitation at 488 nm, the downconversion mechanism in the Er3+/Yb3+ system was investigated and the energy transfers implicated in the emissions of erbium and ytterbium ions were discussed based on the different cross-relaxation processes. The addition of ytterbium resulted in an effective energy transfer from the excited 4S3/2/2H11/2 state of Er3+ ions to the emitting 2F5/2 state of Yb3+ ion, which considerably enhanced NIR emissions at 1000 nm and reduced experimental lifetimes of 4S3/2/2H11/2 states. Through luminescence decay analysis, the maximum values of quantum efficiency (ηQE) and energy transfer efficiency (ηET) were estimated as 61.2% and 161.2%, respectively. This result indicates that the proposed glasses can convert visible photons into NIR emissions at 1000 nm suitable to improve the spectral response of crystalline silicon PV cells.

Volume and surface effects on two-photonic and three-photonic processes in dry co-doped upconversion nanocrystals

Despite considerable advances in synthesizing high-quality core/shell upconversion (UC) nanocrystals (NC; UCNC) and UCNC photophysics, the application of near-infrared (NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence (UCL) of UCNC of small size or thin protecting shell. To obtain deeper insights into energy transfer and surface quenching processes involving Yb3+ and Er3+ ions, we examined energy loss processes in differently sized solid core NaYF4 nanocrystals doped with either Yb3+ (YbNC; 20% Yb3+) or Er3+ (ErNC; 2% Er3+) and co-doped with Yb3+ and Er3+ (YbErNC; 20% Yb3+ and 2% Er3+) without a surface protection shell and coated with a thin and a thick NaYF4 shell in comparison to single and co-doped bulk materials. Luminescence studies at 375 nm excitation demonstrate back-energy transfer (BET) from the 4G11/2 state of Er3+ to the 2F5/2 state of Yb3+, through which the red Er3+4F9/2 state is efficiently populated. Excitation power density (P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and three-photonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+ emission. The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core. We provide a three-dimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC.

Impacts of glass homogenization on optical properties of rare-earth ion doped chalcogenide glass

In rare-earth ion doped chalcogenide glass, the impacts of glass homogenization on optical properties were studied in this work. A series of Ge24Ga10Se65:Er1 glasses were fabricated by melt-quenching method under the same condition with different melting time. The structure of the obtained glasses was characterized, absorption and emission spectra were recorded, and lifetime of the 4 I13/2 state of Er3+ ions was measured as well. It is found that the melting time does not have obvious influence on glass structure, absorption and emission properties of erbium ions. A significant improvement on lifetime was noticed with the increase of melting time.

Synthesis and upconversion luminescent properties of Bi2MoO6:20%Yb3+, 2%Er3+ hollow microsphere with different W6+ ions doping

In this work, W6+ ions doped Bi2MoO6:20%Yb3+, 2%Er3+ samples were successfully synthesized by a facile and modified hydrothermal method. The main morphology of Bi2MoO6 samples were hollow microsphere structure assembled by nanosheets. The particle size was slightly increased as enhancing W6+ ions doping concentration to 5%, then decreased as the doping concentration increased. Besides, doping W6+ ions can increase the band gap of products from 2.65 ​eV to 2.71eV. The upconversion emission intensity of all samples was strongly influenced by the W6+ ions doping concentration. The luminescent intensity enhanced with the doping concentration increasing up to 3%, then decreased when the W6+ ions concentration further increased. Moreover, the intensity of red emission increased by a large margin than that of green-light region. Besides, the lifetime of 4F9/2 states of Er3+ ions for Bi2MoO6:20%Yb3+, 2%Er3+, 3%W6+ (τ655 ​= ​583.64 ​μs) had significant longer lifetime relative to the Bi2MoO6:20%Yb3+, 2%Er3+ (τ655 ​= ​70.29 ​μs).

Comparative Study of Er3+ Ions Doped Phosphate Based Oxide and Oxy-fluoride Glasses for Lasers Applications

Abstract Er3+ ions doped sodium strontium gadolinium oxide and oxy-fluoride phosphate glass samples prepared by conventional melt quenching technique. The samples were melted at 1200 °C in electric furnace with alumina crucibles. The densities of the samples were measure with the help of Archimedes principle using water as immersion liquid. The refractive index (n) was measured by Abbe refractometer with a sodium-vapour lamp as a light source and using mono-bromonaphthalene (C10H7Br) as a contact liquid. The prepared glass samples were characterized with UV-Vis-NIR absorptions and NIR photoluminescence. The UV-Vis-NIR spectra show peaks at 379, 406, 488, 521, 548, 652, 803, 977, and 1536 nm which are due to the transitions from 4 I15/2 ground state to 2H9/2, 4F3/2, 4F7/2, 4H11/2, 4S3/2, 4F9/2, 4I11/2 and 4I13/2 exited states of Er3+ ions, respectively. In NIR emission one broad peak at 1543 nm is observed in present glass samples with 379 nm excitation. From NIR emission it is observed that the FFEr glass give better emission intensity than the GEr and FEr. McCumber theory was used to evaluate stimulated emission cross-section of 4I13/2→4I15/2 transition of Er3+ ion using the absorption spectral measurements. Thus, these results show that present glasses have the potential for use in efficient short and conventional-length optical amplifiers and tuneable lasers

A three-mode self-referenced optical thermometry based on up-conversion luminescence of Ca2MgWO6:Er3+,Yb3+ phosphors

To develop new up-conversion luminescent materials for optical thermometry, a sequence of Ca2MgWO6:xEr3+,yYb3+ phosphor samples were synthesized via high temperature solid-state reaction method. Their structure, morphology and luminescent performances were completely explored via X-ray diffraction, scanning electron microscopy and photoluminescence. Excited by 980 nm laser, all phosphor samples emit intense up-conversion luminescence of Er3+ at 531, 549 and 661 nm. Besides, these emissions were greatly enhanced with addition of Yb3+ ions. Benefiting from the different temperature dependence of three emission peaks, a dual-mode temperature sensor based on fluorescence intensity ratio (2H11/2/4S3/2 and 2H11/2/4F9/2) is realized by using single luminescent center. Meanwhile, the fluorescence lifetime of 4S3/2 state of Er3+ ions was used as the third temperature detection signal. More importantly, the phosphors exhibit superior thermal stability that will be helpful to obtain high precision temperature measurement. All results show that Ca2MgWO6:Er3+, Yb3+ samples could have potential applications for self-referenced optical thermometry.

Improved green upconversion emissions from CaWO4: Er3+-Yb3+ by Cr3+ codoping for optical thermometry

Optical temperature sensors based on rare earth ions activated luminescent materials have presented their capabilities in thermal reading with good stability and high spatial resolution. The ongoing challenge is to improve the luminescence for further enhancing temperature measurement sensitivity and accuracy. Here, several Er3+-Yb3+ codoped CaWO4 phosphors are prepared and Cr3+ ions are introduced, trying to modify the upconverion (UC) emissions from Er3+ ions. Under the excitation of 980 nm laser, green UC luminescence from 2H11/2 and 4S3/2 states of Er3+ is successfully strengthened with Cr3+ codoping. Through the analysis of characterization by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and time-resolved spectroscopy, it is found that the dopant of Cr3+ ions could affect the crystallinity and distort the crystal structure of the as-prepared samples. The thermometry behavior based on green emissions of Er3+ is studied via fluorescence intensity ratio method. It is interesting to observe that the temperature sensing performance has also been influenced by the incorporation of Cr3+. When introducing 9 mol% Cr3+ ions into Er3+-Yb3+ codoped CaWO4 phosphors, a maximum sensitivity of about 1.91% K−1 has been achieved. Combined with the intense green luminescence, CaWO4: Er3+-Yb3+-Cr3+ would be a promising candidate for optical thermometry with excellent measurement sensitivity and accuracy.

Origin of strong red emission in Er3+-based upconversion materials: role of intermediate states and cross relaxation.

Among the various upconversion (UC) materials, sodium yttrium fluoride doped with ytterbium and erbium (NaYF4:Yb3+,Er3+) is the most widely studied owing to its high UC efficiency. Nonetheless, UC mechanisms are not yet fully understood and, in particular, near-infrared-to-red UC mechanisms are still under debate. Herein, we examine UC mechanisms in Er3+-based UC materials. Most importantly, the 4F3/2 and 4F5/2 states of Er3+ were found to be important intermediate states for strong red emission, for the first time. The cross relaxation between the Er3+ ions, back energy transfer from Er3+ to Yb3+, and relative doping concentrations of Er3+ and Yb3+ in NaYF4:Yb3+,Er3+ were found to play important roles in the relative intensity between red and green emissions. The proposed UC mechanism will provide design principles for various Er3+-based UC materials.

Photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation

In the present work, down- and up-conversion photoluminescence properties of Er3+/Yb3+ doped ZrO2 coatings formed by plasma electrolytic oxidation of zirconium in electrolyte containing Er2O3 and Yb2O3 particles were investigated. Down-conversion PL analysis shows that emission spectra of ZrO2:Er3+/Yb3+ coatings excited with 280 nm radiation are composed of broad PL band related to ZrO2 host and bands assigned to f-f transitions of Er3+. The main PL emission bands of Er3+ at around 548 nm and 560 nm are related to 4S3/2→4I15/2 transition. PL excitation spectra monitored at 548 nm feature broad band in the region from 250 nm to 350 nm which is associated with the electron transfer transition from 2p orbital of O2− to 4f orbital of Er3+ and transitions of ZrO2. On the other hand, bands in PL excitation spectra ranging from 350 nm to 535 nm are related to 4f transitions of the Er3+ from the ground state 4I15/2 to higher energy levels. Down-conversion PL intensity decreases with increasing concentration of Yb3+ in coating due to energy transfer from Er3+ to Yb3+. ZrO2:Er3+/Yb3+ coatings show intense green (4S3/2→4I15/2) and red (4F9/2→4I15/2) up-conversion PL emission under the excitation with a 980 nm diode laser. With increasing Yb3+ concentration red up-conversion PL intensity increases more rapidly with respect to green emission, because red up-conversion PL intensity strongly depends on Yb3+ concentration, i.e. 4F9/2 state of Er3+ is directly excited by energy transfer from excited Yb3+.

Promising Er3+/Yb3+-Codoped GdBiW2O9 Phosphor for Temperature Sensing by Upconversion Luminescence.

Yb3+/Er3+-codoped GdBiW2O9 phosphors are prepared via the solid-state route for application in upconversion temperature sensors. The structural analyses indicate that all phosphors possess a single-phased orthorhombic structure. Upon the excitation of a laser wavelength of 980 nm, Yb3+/Er3+-codoped GdBiW2O9 phosphors emanate green emission peaks, endorsed to the emission to the 4I15/2 state from the 4S3/2 and 2H11/2 states, respectively, and the weak emission (red) from the 4F9/2 state to the 4I15/2 state of Er3+ ion. The upconversion mechanism has been elucidated via the scheme of energy levels conferred from the pump power-induced upconversion characteristics. The temperature-dependent upconversion of GdBiW2O9 phosphors was investigated in detail along with the estimation of the stability and repeatability of the measurement. The obtained sensitivity data for the present materials with the corresponding sensing parameters show their probable outlook in temperature sensing applications.

Influence of the multiphonon non-radiative relaxation on the luminescence ratiometric thermometry

We take the 2H11/2/4S3/2–4I15/2 transitions of Er3+ as examples to study the role of thermal quenching mechanisms, especially the multiphonon non-radiative relaxation (MNR), in determination of the luminescence ratiometric thermometry. A convenient method to effectively confirm the existence of the quenching mechanism is proposed, namely the piecewise fitting in several small temperature ranges. Based on this method, a series of fitted gaps between the 2H11/2 and 4S3/2 states of Er3+ are obtained, which are found to decrease monotonically with the increase of temperature. Undoubtedly, it suggests that the quenching mechanism is present. Furthermore, it is demonstrated that the MNR process which depopulates the distribution of the 2H11/2 and 4S3/2 states is likely to be mainly responsible for these gradually decreasing gaps.

Tunable phase and upconverting luminescence of Gd3+ co-doped NaErF4:Yb3+ nanostructures

Upconverting NaErF4:Yb3+,Gd3+ nanoparticles (NPs) and nanorods (NRs) with improved red emission have been successfully achieved via a facile hydrothermal route using oleic acid as the assistant surfactant. The crystalline phase, morphology even the size are simultaneously tuned by controlling the reaction temperatures and Gd3+ doping contents. The higher synthesis temperature leads to the morphology evolution from NPs to NRs. The integrated intensity ratio of red to green emissions is much improved for Gd3+ codoping nanostructures. The microstructure characterizations along with the steady and transient spectroscopy are performed to better understand the underlying mechanisms of phase evolution and emission enhancement. For the different states of Er3+, i.e.2H11/2 and 4F9/2, the radiative/non-radiative transition probabilities could be affected by Gd3+ doping in different ways as for NPs and NRs, based on the lifetime and emission intensity data. NaErF4:Yb3+,Gd3+ nanosctructures are expected to have promising applications in multimodal bioimaging for deeper tissue penetration.

Influence of phase transitions on green fluorescence intensity ratio in Er3+ doped K0.5Na0.5NbO3 ceramic.

The fluorescence intensity ratio (FIR) method is a non-contact temperature (T) measurement technique based on thermally coupled levels of rare earth ions in a doped host. Green fluorescence originating from 2H11/2 and 4S3/2 states of Er3+ doped K0.5Na0.5NbO3 (KNN) ceramic are studied in the temperature range of 300 K to 720 K. The fluorescence intensities change dramatically around phase transition points where the crystal symmetry changes, inducing deviation of the FIR from Boltzmann's law. The temperature determined by the FIR method deviates from thermocouple measurements by 7 K at the orthorhombic to tetragonal phase transition (TO-T) point and 13 K at the Curie point (TC). This finding gives guidance for developing fluorescent T sensors with ferroelectrics and may also provide a fluorescent method to detect phase transitions in ferroelectric materials.

Phonon-Assisted Population Inversion in Lanthanide-Doped Upconversion Ba2 LaF7 Nanocrystals in Glass-Ceramics.

The effective population inversion of 2 H11/2 from 4 S3/2 state of Er3+ ions can be achieved through the annihilation of phonons; random lasing action from BLF films embedded with Yb3+ /Er3+ codoped BLF nanocrystals is demonstrated and high ambient temperature (>433 K) operation lasers with a very low excitation threshold (<530 nJ cm-2 ) are realized.

Optical thermometry based on the red upconversion fluorescence of Er3+ in CaWO4:Yb3+/Er3+ polycrystalline powder.

Based on the fluorescence intensity ratio method, the temperature-sensing behavior through thermally coupled levels (TCL) of the H11/22 and S3/24 states as well as the sub-levels of the F9/24 state of Er3+ has been studied. The thermometry is observed to be dependent on the pump power for the H11/22 and S3/24 states, leading to an error of more than 20 K at 478 K. By utilizing the sub-levels of the F9/24 state, such a problem could be solved. The maximum sensitivity is about 0.15% K-1 at 298 K. This will provide guidance on selecting appropriate and practical TCL for precisely sensing the temperature.