Green Upconversion Emission Research Articles

Sol-gel synthesis and optical temperature sensing properties of PbTiO3:Yb3+/Er3+ phosphors

This paper reports a new type of PbTiO3:Yb3+/Er3+ (PTO:Yb3+/Er3+) phosphor synthesized by sol-gel method. Under 980 nm excitation, PTO:Yb3+/Er3+ phosphors exhibited green emission bands centered at 524/549 nm (2H11/2/4S3/2 → 4I15/2) and red emissions 661 nm (4F9/2 → 4I15/2). Concentration-dependent upconversion (UC) luminescence spectra showed that the optimal luminescence was observed at 6at%Yb3+/2at%Er3+-codoping concentration. A possible UC mechanism for PTO:Yb3+/Er3+ phosphor is discussed by the pump power-dependent UC luminescence spectra. The temperature-dependence (298–548 K) of the fluorescence intensity ratios (FIR) for the two green UC emission bands peaked at 524 and 549 nm was studied under a 980 nm laser excitation and the maximum relative sensitivity was approximately 12.25 × 10−3 K−1 at 298 K. The thermal quenching activation energy of near-infrared (NIR) luminescence was studied. It can be found that the phosphor has a small thermal quenching possibility and excellent thermal stability. The value of repeatability (R) more than 98% has obtained via four cycles of cooling and heating, which prove that the phosphor has a good cycling stability. These results indicate that PTO:Yb3+/Er3+ phosphor is a promising candidate for optical temperature sensors with high sensitivity and good repeatability.

Study of near-infrared induced color tunability and optical bistability in Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor

This work reports the green to red color tunable upconversion emission in a newly synthesized Ho3+/Yb3+ codoped YV0.75Ta0.25O4 phosphor, prepared by solid-state reaction (SSR) method. The crystal phase formation has been confirmed by X-Ray diffraction analysis. The Fourier transform infrared (FTIR) spectrum show bands at different frequencies due to V-O and Ta-O, and found to play a vital role in relaxation (radiative and non-radiative) processes. The synthesized phosphor sample show intense upconversion (UC) emission in green (∼539 nm), red (∼659 nm) and in near infrared (NIR∼ 754 nm) regions on 980 nm laser excitation. These bands appear as a result of (5F4+5S2→5I8), (5F5→5I8) and (5F4+5S2→5I7) transitions of Ho3+ ion, respectively. The tunability in color from green to orange-red is observed on varying the pump power of NIR laser (980 nm excitation). The intrinsic optical bistability is observed in both, green & red upconversion bands with the increase and decrease in power of NIR source. The Ln I-Ln P plots suggest that green & red UC emissions are due to two photon absorption at low laser power. A decrease in the slope values at higher pump powers confirms the laser induced optical heating (LIOH) in the material. The pump power based color tunable emission and optical bistability can be utilized in security detection, optical memory, optical color coding, color switching and in various advanced applications.

The upconversion luminescence from visible to near-infrared in pyrosilicate C-Er2Si2O7

Rare earth pyrosilicate C-Er2Si2O7 ceramics were synthesized by the conventional solid-state reaction method. We observed strong photoluminescence (PL) peaks of Er3+ around 1546 nm with a lifetime of 135.4 μs at room temperature, which is longer than that of Er2Si2O7 films fabricated on Si substrate. Under 980 nm excitation, obvious blue, green, and red upconversion (UC) emissions of Er3+ are observed in this material, making C-Er2Si2O7 a potential material for color display. The luminescence mechanism that two and three photons participate in the energy level excitation was analyzed. Moreover, the near-infrared UC emission in the first biological window was also observed in C-Er2Si2O7, indicating that this material can be used in the in vivo field.

Green, red, and near-infrared up-conversion emission of NaY(MoO4)2:Er3+ submicrometric particles obtained by one-step synthesis, and its thermometric application

Lanthanide ion-based nonlinear optical processes for conversion of infrared radiation to visible radiation are well known. These processes have been used to produce efficient photonic devices for optical amplifiers in Telecom, bioimaging systems, solid-state lasers, temperature sensors, displays, and solar cells. Here, we obtained submicrometric spherical NaY(MoO4)2:Er3+ particles doped at 0.5, 1, 2, 5, 10, 15, and 20% (mol/mol, Er3+/Y3+ ions) by spray pyrolysis in one step, and we studied up-conversion emission as a function of the lanthanide ion content in the matrix. Characterization of the samples by XRD, FTIR, TEM, and luminescence spectroscopy confirmed that spherical particles with micro- and submicrometric diameters were produced. All the samples had tetragonal structure with space group I41/a. The up-conversion studies performed upon excitation at 980 and 1550 nm confirmed a two- and three-photon mechanism, respectively. The emission behavior depended on the Er3+ content, and the materials emitted photons in the green, red, and NIR region. In addition, color emission could be tuned by the Er3+ content. Next, we studied the up-conversion behavior of the materials as a function of temperature. Spectroscopy showed that the integrated intensity emission from thermally coupled levels (2H11/2 and 4S3/2) depended linearly on temperature. The particles obtained here could be useful sensitizers for solar cells, bioimaging systems, and luminescent thermometry devices.

Interfacial Stress‐Modulated Mechanosensitive Upconversion Luminescence of NaErF4 Based Heteroepitaxial Core–Shell Nanoparticles

AbstractThe resulting interfacial stress in heteroepitaxial nanocomplex usually has negligible influence on its performance, but at high pressures (HP) the effect can be significantly amplified. In order to unravel the underlying mechanism and search for high quality pressure sensors, a simple object is employed, NaErF4@NaLnF4 (Ln = Y, Lu, Gd) and its Tm3+‐doped derivatives, to comparatively study the effect of interfacial stress on upconversion (UC) luminescence. Specifically, the doping enhances greatly mechanosensitivity because of the anisotropic local geometry of the dopant ions of which the structural distortion is amplified by HP. The generated compressive strain does extend into the core as witnessed by the effect of tensile strain in the shell on the core and the fact that Lu‐shelled nanoparticles are the most sensitive to external force among Tm3+‐doped system. This compressive strain in concert with the external HP intensifies the coupling between Er3+ and Tm3+, making the attenuation of green UC emission more pronounced. The red to green UC emission ratio of this material, robust both in structural and optical properties, increases linearly with pressure in the range from ambient to 9 GPa. The study opens a new horizon for understanding the effect of interfacial stress on UC luminescence.

In Situ Synthesis of β-Na1.5Y1.5F6: Er3+ Crystals in Oxyfluoride Silicate Glass for Temperature Sensors and Their Spectral Conversion and Optical Thermometry Analysis.

Transparent oxyfluoride glass-ceramics (GCs) with embedded β-Na1.5Y1.5F6 crystals doped with Er3+ ions were fabricated by a melt-quenching method with subsequent heat-treatment. The structural characterizations and spectroscopic techniques were performed to verify the precipitation of β-Na1.5Y1.5F6 crystals and partition of the Er3+ dopant into the crystals. Bright green up-conversion (UC) emission was achieved in Er3+-doped glass-ceramic (Er-GC). Furthermore, the temperature-dependent visible UC behavior based on thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs) was also examined in the temperature range 298 k to 823 K with maximum relative sensitivity (Sr) of 1.1% K−1 at 298 K for TCLs in Er-G and Er-GC samples.

Efficient dual-mode emissions of high-concentration erbium ions doped lead-free halide double perovskite single crystals

Lead-free halide double perovskites have attracted great attention due to the intriguing optoelectronic properties. However, the related researches mainly focus on their down-shifting (DS) luminescence process，while the up-conversion (UC) luminescence process is still rarely studied. Herein, Er3+ ions doped Cs2Ag0.6Na0.4InCl6:0.3%Bi double perovskite single crystals were prepared by an improved hydrothermal method, and the efficient UC and DS emission of Er3+ ions were realized by high-level doping concentration of Er3+ ions. Interesting, the UC green emission of Er3+ ions can be all obtained under 808，980 and 1540 nm excitation, and the optimal photoluminescence quantum yield (PLQY) is 0.17%. To be emphasized, it is the UC luminescence of rare earth ions doped semiconductor materials, which is more advantages in the application of optoelectronic devices than the UC luminescence of rare earth ions doped insulator materials (e.g, NaYF4). Moreover, with the increase of Er3+ ions doping concentration, the DS luminescence color can be controlled from yellow to green. And the near-infrared (NIR) light with the peak at 1540 nm is simultaneously emitted, and the highest PLQY reaches 38.36%, which is suitable for optical communication. Notably, the NIR light (1540 nm) can be also obtained under 808 and 980 nm excitation, which has positive significance for biological applications. This work demonstrates that rare earth ions doping has the potential to impart new functions to double perovskites.

Optical thermometry through infrared excited green upconversion emissions of Er3+ -Yb3+ co-doped LaAlO3 phosphors

Er3+/Yb3+ single- and co-doped LaAlO3 ceramic phosphors have been synthesized by the conventional solid-state reaction method. The structural, morphological, and optical properties of (z at. %) Er: LaAlO3, (1 at.% Er), (y at.% Yb): LaAlO3, and (7 at.% Yb), (x at.% Er): LaAlO3 samples were investigated. The upconversion (UC) luminescence spectra of (Er3+, Yb3+): LaAlO3 phosphors exhibit strong green and weak red emissions under 973 nm excitation. By measuring the power dependence of the UC emission intensity, it was shown that the 4S3/2, 2H11/2, and 4F9/2 levels responsible for the green and red emissions, respectively, are populated by two-photon processes. The luminescence decay of the 4S3/2 (Er3+) level was analyzed. The luminescence intensity ratio (LIR) temperature dependence for the thermally coupled levels (2H11/2 and 4S3/2) of Er3+ ions in (1 at. % Er, 7 at. % Yb): LaAlO3 sample was calculated and the variations of absolute thermal sensitivity (Sa) and relative thermal sensitivity (Sr) with temperature were determined. The maximum values obtained for the Sr and Sa parameters were Sr = 2.44% K−1 at 175 K and Sa = 0.0048 K−1 at 400 K. The results show that (Er3+, Yb3+): LaAlO3 ceramic phosphors are suitable upconverting materials for green display devices and present great potential as non-contact optical temperature sensors.

Bright green up-conversion luminescence of LaNbO4: Nd3+/Yb3+/Ho3+ phosphors under 808 nm and 980 nm excitations and the effects of dopant concentration

LaNbO4: Nd3+/Yb3+/Ho3+ phosphors with various concentrations of Nd3+, Yb3+ and Ho3+ were prepared by a traditional high temperature solid-state reaction method. The crystal structure of the as-prepared samples was characterized by X-ray diffraction (XRD) and the results showed that monoclinic LaNbO4 samples were obtained. Green and red up-conversion (UC) emissions of Ho3+ were observed under the excitations of 808 nm and 980 nm. Concentration dependent studies indicated that Nd3+ and Yb3+ played different roles in the UC emissions of Ho3+ under different wavelength excitations. The same optimal concentrations of Yb3+ and Ho3+ ions were obtained when excited by 808 nm and 980 nm lasers. The UC luminescence mechanisms under different excitation sources were discussed by detecting the UC luminescence intensity related to the laser pumped power density. The energy transfer efficiencies from Nd3+ to Yb3+ and Yb3+ to Ho3+ were confirmed via lifetime measurement. By comparing with the commercial green NaYF4: Er3+/Yb3+ UC luminescence phosphor, the UC luminescence performance of Ho3+ doped sample was evaluated. The results showed that LaNbO4: Nd3+/Yb3+/Ho3+ phosphors had excellent green UC luminescence properties under both 808 nm and 980 nm excitations.

Structural, luminescent and upconversion characteristics of Er3+ doped titanium zinc tellurite glass

The TeO 2 –TiO 2 –ZnO glass was single doped with Er 3+ and its structural, luminescent, and upconversion properties were analyzed. The amorphous nature of the fabricated glass was confirmed by X-ray diffraction, and the characteristic vibrational modes of the tellurite-titanium-zinc glass network were identified by Raman spectroscopy. The photoluminescent and upconversion properties of Er 3+ doped glass was analyzed by time decay measurements at different excitation wavelengths. The spectra recorded upon excitations at 808 nm and 975 nm show an intense green upconversion luminescence corresponding to the 2 H 11/2 , 4 S 3/2 → 4 I 15/2 transitions and a very weak red emission associated to the 4 F 9/2 → 4 I 15/2 transition. The experimental results suggest that in Er 3+ doped glass the excited state absorption and/or energy transfer mechanisms are responsible for upconversion luminescence observed upon 808 nm and 975 nm excitations. • TeO–TiO 2 –ZnO glasses optically activated with Er 3+ single doping. • Up-conversion luminescence takes place as a double photon absorption process. • Up-conversion produced by excited-state absorption and/or energy transfer mechanism. • Intense green up-conversion emission upon 808 and 975 nm excitation.

Synthesis of NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 nanorods and their size dependent uptake efficiency under flow condition

Lanthanide doped fluorescent nanoparticles have gained considerable attention in biomedical applications. However, the low uptake efficiency of nanoparticles by cells has limited their applications. In this work, we demonstrate how the uptake efficiency is affected by the size of nanoparticles under flow conditions. Using the same size NaYF4:20% Yb3+,2% Er3+,2% Ce3+ (the contents of rare earths elements are in molar fraction) nanoparticles as core, NaYF4:20% Yb3+,2% Er3+,2% Ce3+@NaYF4 core–shell structured nanorods (NRs) with different sizes of 60–224 nm were synthesized by thermal decomposition and hot injection method. Under excitation at 980 nm, a strong upconversion green emission (541 nm, 2H11/2 → 4I15/2 of Er3+) is observed for all samples. The emission intensity for each size nanorod was calibrated and is found to depend on the width of NRs. Under flow conditions, the nanorods with 96 nm show a maximum uptake efficiency by endothelial cells. This work demonstrates the importance of optimizing the size for improving the uptake efficiency of lanthanide-doped nanoparticles.

The enhanced up-conversion green by Yb-Mn dimer in NaBiF4:Yb3+/Er3+/Mn2+ for optical fiber temperature sensor

Through doping Mn2+ into the NaBiF4:Yb3+/Er3+, it can be achieved that NaBiF4 :Yb3+/Er3+/Mn2+ possess superior temperature sensing performance and application in temperature optical fiber sensing on the premise of enhancing the green emission upon the 980 nm excitation. The effect of Mn2+ content on the phase and luminescence of NaBiF4:Yb3+/Er3+/Mn2+ is investigated by X-ray diffraction (XRD) and fluorescence spectrophotometer characterization. The up-conversion (UC) green emission intensity is enhanced by 3 times by Mn2+ doping. The Yb3+-Mn2+ dimer is introduced to clarify the mechanism of UC red and green emission enhancement, where involved in is three-photon process. Moreover, the optical thermometric behaviors of the synthetic compounds are analyzed according to the fact that Er3+ processes a couple of green emission levels 2H11/2 and 4S3/2, and the maximum Sa (absolute sensor sensitivity) reaches 0.00559 K−1. The preliminary design and application of NaBiF4:Yb3+/Er3+/Mn2+ as a probe in the temperature optical fiber sensor has been carried out, suggesting that NaBiF4: Yb3+/Er3+/Mn2+ is expected to be a kind of promising material for non-contact optical thermometer.

The investigation of Er3+ fluorescence properties on femtosecond-laser-written LiNbO3 dual-line and depressed-cladding waveguides

The dual-line and depressed-cladding waveguides are fabricated by femtosecond laser (fs-laser) in Er3+, MgO co-doped nearly stoichiometric LiNbO3 (Er3+:MgO:NSLN) crystals. Single-mode propagation at 1064 nm can be supported inside both two waveguides, in which the 980 nm excited green up-conversion emission can be enhanced. The confocal micro-photoluminescence (µ-PL) spectroscopy has been performed to investigate the changes of Er3+ fluorescence properties in fs-laser modified regions. Under 980 nm excitation, the fluorescence intensity of green up-conversion and near-infrared (NIR) emission is reduced by ~5% in modified areas. However, there is an increase for intensity of 532 nm excited Er3+ emission line (at ~1550 nm). Our work paves a way for fabricating novel waveguide amplifiers as well as lasers, and studying physical mechanism on fs-laser-processing of Er3+:MgO:NSLN crystals.

Dual-ratiometric thermometry of Erbium(Ⅲ) in electrospun fibers inlaid with BaMgF4 microcrystals

(Ba1−x−yErxYby)MgF4/PAN (BMF-EY/PAN) fibers have been prepared by electrospinning technique, in which composite fibers vested with smooth surface, excellent flexibility and self-calibration temperature sensing function. Under 977 nm laser excitation, the strong green and red up-conversion (UC) emissions produced by the flexible fibers through effective UC luminescence are considered to be a two-photon absorption process, attributing to 2H11/2/4S3/2 → 4I15/2 and 4F9/2 (Ⅰ)/4F9/2 (Ⅱ) → 4I15/2 radiation transitions of Er3+, respectively. Combined utilization of green (523 and 545 nm) and red (656 and 669 nm) emissions endows the composite fibers with the potential in microdomain temperature sensing, realizing the accurate temperature acquisition in complex environment. At a relatively moderate working temperature (363 K), the absolute (SA) and relative (SR) sensitivity values in fibers based on green-emission reach up to 0.351 and 0.824 %K−1 for main sensing, and correspondingly, the values depended on red-emission are 0.342 and 0.302 %K−1 for auxiliary sensing, respectively. Composite fibers inlaid with crystallites have superior performances in luminescence, thermal feedback and flexibility, providing a breakthrough for the development of temperature-sensing materials in biomedical field.

Yb,Ho:(La0.1Y0.9)2O3 ceramics for thermometric applications based on the upconversion emission

A series of Yb,Ho:(La0.1Y0.9)2O3 green-emitting upconversion (UC) ceramics were fabricated by the spark plasma sintering (SPS) method. Under the 980 nm excitation, the samples exhibited strong green, weak red and negligible near infrared (NIR) UC emissions, corresponding to the transitions 5F4/5S2→5I8, 5F5→5I8 and 5F4/5S2→5I7 of Ho3+ ions, respectively. The UC emission intensity of Yb,Ho:(La0.1Y0.9)2O3 ceramics can be optimized by appropriate concentration of Yb3+. In addition, optical temperature sensing properties of Yb,Ho:(La0.1Y0.9)2O3 ceramics were investigated in the range of 303–573 K, presenting a maximum relative sensitivity of about 0.017 K−1 at 573 K. The results demonstrate the Yb,Ho:(La0.1Y0.9)2O3 ceramic can be a potential candidate for temperature sensors.

Efficient white upconversion luminescence in Yb3+/Eu3+ doubly-doped transparent glass ceramic.

Efficient white upconversion (UC) luminescence is obtained in Yb3+/Eu3+ doubly-doped optical glass ceramic (GC) for the first time. KYb3F10 nanocrystals are controllably precipitated from the amorphous networks via the inducing of Yb3+. Yb3+ ions are spontaneously confined within the compact fluoride crystal structures to produce efficient blue UC emissions of Yb3+-Yb3+ pairs. Eu3+ ions are easily incorporated into the KYb3F10 crystal lattices. Owing to the extremely short interionic distance in the crystal structures, intense green UC emissions apart from the red emissions of Eu3+ are observed, which are not obtained by the traditional Yb3+/Eu3+ doubly-doped GCs. As a result, white UC emissions are synthesized based on the three-primary-color principle and the emission intensities of GCs are dramatically enhanced as compared to glass. The designed GCs provide novel optical gain materials for the promising applications in three-dimensional display, solid-state lighting and tunable fiber lasers.

Tuning the structural and luminescence properties of LiYF4:Yb, Er upconversion phosphor: Understanding the role of K ion concentration

Influence of K+ ion concentrations on the upconversion emissions of LiYF4: Yb, Er phosphor has been investigated. Li1−xKxY0.77F4:Yb0.2, Er0.03 phosphors are synthesized by solid-state reaction method under reduced atmosphere. X-ray diffraction analysis revealed a major phase transition from tetragonal LiYF4 to hexagonal KYF4 as the concentration of K+ ion increases. Blue, green and red upconversion emissions are observed when the samples are excited at 980 nm. Green and red luminescence intensities are affected by the inclusion of K+ ion concentrations in the host lattice. Downshifting photoluminescence and the corresponding decay analysis are carried out for the Li1−xKxY0.77F4:Yb0.2, Er0.03 phosphors under the excitation wavelength of 378 nm. Significant changes in the emission intensity of the green to red ratio suggest the tuning of the emission color with the modification of the K+ ion concentrations in Li1−xKxY0.77F4:Yb0.2, Er0.03 host and such successful tuning in the color of emission can find potential applications in the field of display devices.

Highly colloidal luminescent Er3+, Yb3+-codoped KY3F10 nanoparticles for theranostic applications

Highly colloidal luminescent nanoparticles (NPs) 5 at% Er3+, 20 at% Yb3+:KY3F10 were prepared by EDTA assisted hydrothermal method. Spherical and monodispersed Er3+, Yb3+:KY3F10 nanoparticles with highly pure cubic phase exhibit attractive optical properties for their use in long-term biological studies because of the high chemical photo-stability and strong emissions in the visible and near infrared (NIR) regions. The luminescence spectra of Er3+, Yb3+:KY3F10 as dried powder and dispersed in physiologic medium show intense green upconversion emission transition in between 510 and 570 nm (2H11/2→4I15/2 and 4S3/2→4I15/2) and red upconversion emission transition in between 635 and 680 nm (4F9/2→4I15/2) under NIR light excitation (980 nm). The cellular nontoxicity of as-prepared Er3+, Yb3+ codoped KY3F10 to glioblastoma multiforme (GBM) cells, were reported for the first time to our knowledge. This nanomaterial shows potential use for theranostic applications in early detection of brain cancer, acting as biomarkers in the visible and NIR ranges, and as drug activators for some photobiological response as a coadjuvant therapy for cancer treatment, such as photodynamic therapy (PDT).

Electrospinning-derived YVO4:Er/Yb nanowires and nanotubes with temperature sensitivity of their up-converted emission

YVO4:Er/Yb nanowires and nanotubes phosphors were prepared by electrospinning technique following calcination at different heating rates. The obtained nanowires are of 80–200 nm in diameter and are single crystals or polycrystalline in phase. The outer diameter of the obtained nanotubes is 50–200 nm with a wall thickness of 20–30 nm. The up-conversion properties of YVO4:Er3+/Yb3+ nanowires and nanotubes were investigated. All samples were found to produce a green up-converted emission. The temperature-sensing features of YVO4:Er3+/Yb3+ nanowires and nanotubes were investigated through the fluorescence intensity ratio approach, and the sensitivity of temperature was determined over the temperature range of 30–390 °C. The temperature sensing sensitivities of the mixed YVO4:Er3+/Yb3+ nanowire samples and nanotubes exceeded the single YVO4:Er3+/Yb3+ nanowire samples because of higher Yb3+-doped concentrations. The morphology influence on optical properties was studied at a fixed doping rare earth concentration and size. The temperature sensitivities of YVO4:Er/Yb samples depended on the Yb ion concentrations rather than the morphology. The significant temperature sensitivity indicates its potential for use as an optical temperature sensing probe.

Up-conversion and 2 µm mid-infrared emission effective enhancements in Ho3+/Yb3+ co-doped tellurite glass

Rare-earth ions doped fiber lasers at 2 µm can supply various applications in daily life. In this paper, Ho3+/Yb3+ co-doped tellurite glasses were prepared by the high temperature melting method to obtain a strong 2 µm mid-infrared fluorescence emission. The characterization results of the X-ray diffraction (XRD) and differential scanning calorimeter (DSC) show that this glass possesses good crystallization resistance and thermal stability, and its ΔT is 136 °C, which can be successfully drawn. Under the 980 nm LD excitation, strong green (550 nm) and red (660 nm) up-conversion emission were obtained, meanwhile, intensive 2 µm mid-infrared emission was also achieved, and the emission intensity was significantly improved with the increase of Yb3+ concentration, when the Yb3+ content was 2.0, the 2 µm mid-infrared emission intensity was increased by about 28% compared with the content of 0.5, it should be noted that the concentration of Yb3+ is required to be strictly controlled to prevent concentration quenching. In addition, the luminescence process of Ho3+ was further elaborated through the energy transfer mechanism. All results indicate that the Ho3+/Yb3+ co-doped tellurite glass can be an attractive candidate for up-conversion and mid-infrared fiber laser materials.