Upconversion Luminescence Intensity Research Articles

Erbium-ytterbium containing upconversion mesoporous bioactive glass microspheres for tissue engineering: luminescence monitoring of biomineralization and drug release.

The development of functional biomaterials with real-time monitoring of mineralization processes, drug release and biodistribution has potential applications but remains an unsolved challenge. Herein, erbium- and ytterbium- containing mesoporous bioactive glass microspheres (MBGs:Er/Yb) with blue and red emission at an excitation wavelength of 980nm were synthesized by a sol-gel combined with organic template method. As the concentration of Yb3+ ions gradually increases, the emission intensity of the MBGs:Er/Yb exhibits a clear concentration quenching effect. Combined with in vitro bioactivity tests, the optimal molar ratio of Er3+/Yb3+ was determined to be 4:3. Therefore, MBGs:4Er/3Yb was selected for in vitro biomineralization and drug release monitoring. The results of biomineralization monitoring show that the upconversion luminescence intensity is closely related to the degree of biomineralization. The upconversion luminescence intensity of MBGs:4Er/3Yb is quenched with the increase of the degree of biomineralization. The degree of luminescence quenching during biomineralization can be semiquantized. Drug release monitoring experiments showed that the anticancer drug doxorubicin hydrochloride (DOX) was successfully loaded into MBGs:4Er/3Yb and selectively quenched the green emission. When DOX was released, the green emission recovered stably, and It/I0 increased gradually. Moreover, there was a linear relationship between It/I0 and cumulative drug release, indicating that DOX-MBGs:4Er/3Yb is highly sensitive to DOX release, and monitoring the It/I0 values of DOX-MBGs:4Er/3Yb can achieve real-time tracking of the DOX release process to a certain extent. In conclusion, MBGs:4Er/3Yb has potential application as an upconversion luminescence biomonitoring material in the field of bone tissue engineering. STATEMENT OF SIGNIFICANCE: Mesoporous bioactive glasses have great potential for applications in bone tissue repair due to their excellent biological properties, but the effective information of the repair process cannot be grasped in a timely manner. Therefore, real-time monitoring of mineralization and drug release processes will be beneficial to obtain the degree of healing and optimize the amount and distribution of drugs to improve targeted therapeutic effects. For biomaterials, in vitro biological properties determine their biological properties in vivo, where the environment is more complex and diverse, and thus in vitro biomonitoring is particularly crucial. The organic combination of physical properties and biological properties will also provide a feasible idea for the development of biomaterials.

Low threshold photon avalanche upconversion emission for temperature sensing based on Yb(III)/Er(III) Co-doped NdVO4 with sphere 3D self-assembled structure microparticles

Upconversion luminescent microcrystals (UCMs) due to their optical characteristics have been applicated in temperature detecting fields. However, the accuracy of traditional temperature probes based on UCMs is limited by the low intensity of upconversion luminescence (UCL). Herein, Yb3+ and Er3+ ions co-doped NdVO4 (NdVO4:Yb/Er) UCMs with a 3D self-assembled structure were designed via a hydrothermal method. This innovative structure enables the realization of a photon avalanche (PA) emission process. The Yb3+ and Er3+ co-doping in NdVO4:Yb/Er UCMs significantly reduces the PA threshold compared to NdVO4:Er UCMs. Obvious PA process produced by Yb3+/Er3+ doping is observed at low excitation threshold (～13 mW) in NdVO4:Yb/Er UCMs, enhancing the whole UCL intensity. Additionally, the NdVO4:Yb/Er UCMs exhibit a high temperature sensitivity of 3.5% K−1 at low pump power, indicating that UCMs have the potential application in optical temperature sensor.

SPR studies in PVA composite films of SiO2@NaYF4:Er3+/Yb3+ UCNPs via AuNPs concentration variation and their temperature sensing applications

The composite film of mesoporous silica coated NaYF4:Er3+/Yb3+ upconversion nanoparticles and gold nanoparticles (AuNPs) in Poly vinyl alcohol (PVA) medium were prepared. The effect of the concentrations of AuNPs with 0 µl, 50 µl, 100 µl and 150 µl on the structure and upconversion luminescence intensity were studied. The phenomenon of enhancement in upconversion luminescence intensity due to AuNPs were explained via surface plasmon resonance (SPR) phenomenon. Apart from this the XRD, FE-SEM and AFM studies were done for estimation of structure and surface morphology etc. The impurities were estimated through FTIR analysis. The optical properties of these polymer composite films were studied via UV–vis absorption spectra and upconversion luminescence spectra analysis. A low temperature sensing ability of these films have been demonstrated for the suitability of these films in bio-medical applications.

Simple express precursor synthesis of erbium-doped yttrium oxide luminescent material for optical thermometry

A new, simple and inexpensive method for the preparation of nanosized (Y1-xErx)2O3 oxides, including the stages of synthesis and thermolysis of Y1-xErx(HCOO)3 precursors, has been developed. The precursors were obtained by the interaction of mixtures of yttrium and erbium nitrates with formic acid. The effect of erbium concentration on the structure, morphology, and optical properties of (Y1-xErx)2O3 oxides was studied using X-ray diffraction, scanning electron microscopy, and optical absorption methods. Under UV excitation (Y1-xErx)2O3 oxides with 0.005≤x ≤ 0.25 exhibit strong green luminescence related to the 2H11/2/4S3/2 → 4I15/2 transitions and weak red luminescence associated with the 4F9/2 → 4I15/2 transition. According to the CIE chromaticity coordinates, the oxides demonstrate a yellowish-green color emission. A noticeable decrease in the luminescence intensity was recorded for oxides with erbium concentrations above 2.5 mol.% (x = 0.025). Yellowish-green and yellow green upconversion emission resulting from the 4S3/2 → 4I15/2 and the 4F9/2 → 4I15/2 transitions of Er3+ ions were observed upon continuous 980 nm diode laser excitation. When the concentration of erbium in (Y1-xErx)2O3 oxides increases, the luminescence color changes and the intensity of upconversion emission rises. The maximum intensity of upconversion emission was observed for the (Y0.9Er0.1)2O3 oxide. A two-photon upconversion mechanism was established based on the pumping power dependence of UC luminescence intensity. The thermoluminescence characteristics of (Y0.9Er0.1)2O3 oxides based on the ratio of the intensities of the lines corresponding to thermal-coupled 2H11/2 and 4S3/2 levels were determined, the absolute and relative sensitivity values was calculated, and the prospects for using this oxide in non-contact optical thermometers were estimated.

Structural and morphological characterizations of ex-situ sol-gel derived luminescent Nd3+-Yb3+ion co-doped zinc-silicate dense glass-ceramic

We proposed a novel ex-situ sol-gel synthesis of Nd3+ (0.7 mol%) and Yb3+ (X; X = 0.0, 0.7, 1.5, 3.0 mol%) ion co-doped Zinc-Silicate (SZNYX) dense glass-ceramic(DGC) samples. The structural analyses of the SZNY07-DGC sample were performed at different annealing temperatures using X-ray diffraction (XRD) analysis and Fourier transforms infrared (FTIR) spectroscopy. The tetragonal willemite Zn2SiO4 structure with an R-3(148) space group was confirmed from XRD results. The formation of the pure oxide phases (bridging oxygen) was noticed at FTIR spectra with the complete removal of hydroxyl impurity at higher annealing temperatures. The presence of ZnO crystallites with the inter-planer spacing of ⁓ 0.28 nm and Nd3+/Yb3+ ion pair in an amorphous silica host was confirmed via transmission electron microscopy (TEM) and TEM-energy dispersive spectroscopy (EDS) respectively. The white up-conversion luminescence (UCL) under a 980 nm excitation was attributed to the simultaneous emission of wavelength in the visible spectrum. The intensity of UCL was initially rising with an increase in Yb3+ ion concentration whereas the optimized luminescence was obtained for samples with 1.5 mol% Yb3+ ion concentration. The CIE chromaticity coordinates (0.34, 0.35) of corresponding UCL spectra were invariant with the change in Yb3+ ion concentration. The photoluminescence (PL) confocal mapping of the SZNY15-DGC sample was performed at different locations under a 980 nm laser excitation source which turned out non-uniform in nature throughout the surface. Thus as-synthesized SZNYX-DGC samples have spectacular upconversion luminescence for near-infrared excitation which may be utilized in thermal sensing, photovoltaic, displays, and photonic devices.

Upconversion NIR luminescence negative thermal quenching and temperature sensing in LiYGeO4:Yb3+/Nd3+ phosphors

Solid state reaction was used to create LiYGeO4(LYG):Yb3+/Nd3+ phosphors, and upconversion luminescence (UCL) properties were investigated under 980 nm laser stimulation. When only the Yb3+ concentration is altered, and the doping concentration of Nd3+ is kept at 0.02, LYG:0.30 Yb3+/0.02Nd3+ achieves the highest UCL intensity. Because to phonon-assisted transitions and electron thermal migration, considerable near infrared (NIR) UCL negative thermal quenching (NTQ) from Nd3+ is observed with rising sample temperature. The UCL intensity of 4F7/2/4S3/2 → 4I9/2 transition in LYG:0.20 Yb3+/0.02Nd3+ at 723 K is 301.39 times than that at 303 K, and the total UCL intensity of 4F7/2/4S3/2; 4F5/2/2H9/2; 4F3/2 → 4I9/2 transitions attain 24.32 times. Moreover, the temperature sensitive characteristic based on the technology using luminescence intensity ratio (LIR) was systematically evaluated. According to the study, LYG:Yb3+/Nd3+ phosphors exhibit a remarkable NIR UCL NTQ effect and a relative temperature sensitivity (Sr) reaches 1.41% K−1, making them appropriate for application as a photothermal thermometer under high temperature.

Near-infrared photo-responsive Er3+-K+ co-doped Y2O3 phosphors with enhanced UC luminescence

Y2O3: x% Er3+ (x=5, 7, 10, 12, 15) and Y2O3: 10% Er3+，x% K+ (x=0, 1, 3, 5, 7, 10, 15) phosphors were successfully prepared by a low-temperature combustion method. The structure as well as the absorption/emission spectra of phosphors were investigated. The effect of doping concentration of K+ ions on the upconversion (UC) luminescence of Y2O3: 10% Er3+ phosphor was examined and the possible optical transitions were discussed. The results showed that K+ ion doping not only changed the microstructure and crystallinity of the phosphors, but also enhanced its UC luminescence intensity. The Y2O3: 10% Er3+, 7% K+ phosphor exhibit the strongest UC emission intensity. Compared with the Y2O3: 10% Er3+ phosphor, the UC luminescence intensity at 563 nm and 661 nm was enhanced by 67.8 and 27.3 times for the K-codoped samples, respectively. The phosphor with the optimal doping concentration was mixed with a polymer to form a composite film, which was employed for the fabrication of near-infrared (NIR) photo-responsive detection devices. The device exhibited strong photo-current response to NIR light at 980 nm, implying that our work could inspire new design strategy for the development of NIR photo-detection devices.

A sandwiched luminescent heterostructure based on lanthanide‐doped Gd2O2S@NaYF4 core/shell nanocrystals

AbstractLanthanide (Ln3+) oxysulfide nanocrystals (NCs) have great prospect in many advanced technologies; however, they suffer from a low photoluminescence efficiency due to the volatility of sulfur and deleterious surface quenching effect. Herein, we report a novel sandwiched luminescent heterostructure based on Ln3+‐doped Gd2O2S@NaYF4 core/shell NCs with tunable sulfur content in the sandwich layer. By means of Eu3+ as the sensitive structural probes, we unravel the ligand‐mediated structure control of the NCs from Gd2O3: Ln3+@NaYF4 to Gd2O2S: Ln3+@NaYF4 with tailored S2– deficiency. Such a sandwich‐type core/shell heterostructure enables us to achieve efficient and multicolor downshifting and upconversion luminescence (UCL), with up to 208.8 folds of enhancement in UCL intensity as compared to that of their core‐only counterparts. These findings provide a general approach for the controlled synthesis of lanthanide oxysulfide@fluoride heterostructure, which offers a new way for the materials design towards diverse emerging applications.

Enhanced upconversion luminescence in LaVO4:Yb3+/Er3+ nanorods through Ba2+ ions doping

The low efficiency of upconversion luminescence hinders the pratical applications in many optical fields. During the past years, much attention have focused on the fluorides, reports of lanthanum vanadate (LaVO4) in oxides are scarce. Herein, a series of LaVO4:Yb3+/Er3+ crystals codoping with Ba2+ ions are synthesized through one-pot facile hydrothermal route. Many instruments, such as XRD, ICP, TEM equipped with EDS, luminescence spectroscopy are applied to characterize the products. By optimizing the impurity doping content to 15 mol%, the upconversion luminescence intensities of the green and red emissions are enhanced by 23 and 25 times, respectively. A formation mechanism for morphology evolution is proposed. The enhancement of upconversion performance are systematacially investigated upon the grain size, crystal structure symmetry and doping concentration. Moreover, additional operations are carried out by DFT calculations to confirm the experimental result. This work will guide to enhance upconversion performance based on lanthanum vanadate nanocrystals through impurity doping, which may realize the prospective applications in many fields.

Energy transfer and color tunable up-conversion luminescence in PrF3 and YbF3 co-doped SrF2 transparent ceramics

Near-infrared pumped up-conversion luminescent PrF3 and YbF3 co-doped SrF2 ceramics were fabricated by the hot-pressing sintering technique, and the pellets were transparent with a primrose yellow appearance. The influence of YbF3 co-doping levels on the optical qualities and microstructures of ceramics was investigated. We identified the mechanisms to realize up-conversion luminescence in the visible range from 3P0,1 levels (Pr3+) under near-infrared wavelength pumping sources other than the near ultraviolet to blue region photons. Yb3+ ions inducing a broad and intense absorption band at the 900–1050 nm region, and the absorption coefficient and cross-section at 980 nm are 7.57 cm−1 and 4.19 × 10−21 cm2 in the ceramic co-doped with 15 wt% YbF3, respectively. The intense up-conversion luminescence bands at 480, 520, 540, and 600 nm under 980 nm excitation were attributed to 3P0→3H4, 3P1→3H5, 3P0→3H5 and 1D2→3H4 transitions of Pr3+ ions, respectively.

Multiphonon assisted upconversion thermal enhancement for optical temperature sensing and high penetration depth

Thermal quenching that the upconversion (UC) luminescence intensities decrease with increasing temperature limits the application of UC luminescence materials in the field of optical temperature sensing. Herein, we report that Tm3+/Yb3+ doped Gd2O3 phosphors achieve thermal enhancement of UC luminescence with the multiphonon assisted process. Significantly, a possible mechanism of Yb3+ ions in thermal enhancement and multiphonon assisted UC luminescence process is proposed. Based on the luminescence intensity ratio technique of non-thermally coupled energy levels, research shows that thermal enhancement can effectively improve the optical temperature sensing absolute sensitivity. Owing to the near-infrared excitation and strong near-infrared emission, the UC luminescence of the Gd2O3: Tm3+/Yb3+ phosphors can penetrate 12 mm pork tissue and achieve UC thermal enhancement in 287-314 K after penetrating 6 mm pork tissue, which shows its potential in vivo application. The results not only provide a pathway to realize the thermal enhancement of UC luminescence and the improvement of the temperature sensing sensitivity, but also promote the understanding and utilization of the UC luminescence thermal enhancement.

Chiral inorganic nanostructured BiOCl co-doped with Er3+/Yb3+ exhibits circularly polarized luminescence and enhanced upconversion luminescence

It has been challenging to develop lanthanides doped chiral inorganic materials that emit circularly polarized light by upconversion. Here, we report the synthesis of bismuth oxychloride based inorganic nanostructured phosphor co-doped with Er3+, Yb3+, modified with chiral sugar alcohols (D-BYE), which exhibited a strong up-conversion circularly polarized luminescence (UC-CPL) property in the visible range. Compared with the achiral bismuth oxychloride phosphor co-doped with Er3+, Yb3+ (A-BYE), D-BYE significantly improved the intensity of upconversion luminescence. Our studies showed that an accelerated rate of radiative transition induced by electromagnetic field and the Mie scattering effect may be responsible for the enhanced upconversion luminescence. Our works provide a new strategy to realize enhanced upconversion of circularly polarized luminescence with rare earth doped chiral inorganic materials.

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er3+, Tm3+ and Yb3+ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm3+1G4→3H6 transition, 531 and 547 nm (green) from the Er3+2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 transitions, and 640 and 662 nm (red) from the Er3+4F9/2 → 4I15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er2O3, 0.5 mol% Tm2O3 and 2.0 mol% Yb2O3, and this crystal is suitable for use in highly efficient white light emission devices.

Uncovering Different Responses and Energy Mechanisms of Sensitizer and Activator in Host Manipulation for Upconversion Nanoparticles.

Agile and efficient upconversion luminescence (UCL) fine-tuning strategies are the most demanded for in the frontier applications of highly doped upconversion nanoparticles (UCNPs). By doping Zn2+ ions into NaHoF4 and NaGdF4:Yb3+ shells using the oleate method, the separate influences of Zn2+ on Ho3+ and Yb3+ ions in UCL-related processes were analyzed in detail, revealing relevant UCL changes and underlying energy mechanisms from a novel but explicit perspective. Different behaviors of green and red UCL before and after Zn2+-ion doping were attributed to the disparities in the energy pathways and features of the sample structures. Herein, the populations of 5S2/5F4 and 5F5 states, not the usually mentioned decay time, decided the UCL intensities of the NaHoF4@NaYbF4-structured highly doped UCNPs. The advantageous small sizes and intense single-band red UCL of these UCNPs were further developed by combining our previous strategies with introducing Zn2+ ions into the NaHoF4 matrix. Overcoming energy loss by surface quenchers and Zn2+-triggered inner defects is the key factor in maximizing 4f-4f transitions. To the best of our knowledge, the current study is the first attempt to date to experimentally reveal separate impacts of the heteroions on activators and sensitizers in UCL-related processes and can deepen the theoretical investigation of Ho-based UCL for the broadened applications of NaHoF4 UCNPs.

Preparation of the up-conversion glass-ceramics and its synergistic effect on the photocatalytic degradation of photocatalyst

The B2O3–CaF2–Bi2O3 glass-ceramics precipitating CaF2 crystal were prepared by high temperature melting method. The effects of heat treatment schedules, B2O3: Bi2O3 ratio on crystallization behavior and microstructure of base glass were studied. Up-conversion glass-ceramics with Yb3+ as sensitizer and Tm3+ as activator were also prepared, and the effects of Tm3+ doping on their crystallization, microstructure, and up-conversion luminescence performance were analyzed through DSC, XRD, SEM, TEM and PL. To improve further the up-conversion luminescence peformance, Li+ doped up-conversion glass-ceramics and the effect of Li+ doping amount were prepared and explored. The results indicated that the up-conversion luminescence intensity reached its highest when the doping concentrations of Yb3+, Tm3+ and Li + ions were 10 mol%, 0.1 mol% and 6 mol%, respectively. To explore the effect of the prepared up-conversion glass-ceramics on the photocatalytic degradation of ZnIn2S4–Ag–LaFeO3 photocatalyst to dye contaminated model methylene blue (MB), the photocatalytic degradation experiment was carried out by mechanical mixing of up-conversion glass-ceramics and photocatalyst. It was found that the addition of up-conversion glass-ceramics increased the photocatalytic degradation efficiency by 25% under near-infrared light and 7.3% under full spectrum.

A Highly Sensitive Luminescent Upconversion Nanosensor for Turn-On Detection of As3.

A luminescent nanoprobe (NP), MnO2-modified Er3+/Yb3+-codoped Ag2MoO4 upconversion nanoparticles (UCNPs; cod-AMO-3/MnO2), was constructed for rapid, sensitive, and selective "turn-on" detection of trace As3+. Herein, two kinds of luminescent NPs were developed based on luminescence resonance energy transfer (LRET) between cod-AMO-3 as the energy donor and MnO2 as the energy acceptor. By using MnO2 as the matrix in cod-AMO-3/MnO2 fluorometric assay, the upconversion luminescence (UCL) intensity (IUCL) of the cod-AMO-3 probe was quenched significantly through LRET, illustrating MnO2 as an efficient quencher for UCL. With the addition of As3+, a stable bidentate binuclear (BB) corner-sharing bridged complex (As5+-MnO2) was probably formed, which alters the surface of the upconversion NP, leading to gradual separation between UCNPs and MnO2 and subsequent recovery of IUCL. Interestingly, it possessed superior sensitivity, reaction kinetics, and also high selectivity toward As3+ in aqueous solution. Our optimized cod-AMO-3/MnO2 nanocomposite (NComp) demonstrated a linear range of 0-150 ppb and an ultrasensitive detection limit of 0.028 ppb for As3+, which is extremely below the regulatory level, signifying the promising practical usage of this system. To the best of our knowledge, such a surface-modified Ln3+-codoped Ag-based nanosensor being applied for As3+ detection probably has not been reported yet, and it is rather unexplored. In a nutshell, the ability to monitor the As3+ concentration may enable the rational design of a convenient platform for a diverse range of environmental monitoring applications.

Enhanced upconversion luminescence using long-range surface plasmon resonance mode with prism coupler

In the study, we present the significant enhancement of the upconversion luminescence by taking advantage of long-range surface plasmon resonance mode. Compared with the reflection enhanced upconversion luminescence of Ag film, the intensity of upconversion luminescence enhanced by long-range surface plasmon resonance mode is improved 100 times. Additionally, the finite-difference time-domain simulation indicates that the incident light energy can concentrate in the upconversion nanoparticles doped dielectric layer at the long-range surface plasmon resonance mode, which the maximum electric field enhancement factor |E|2/|E0|2 can reach to 58. The experimental result shows that the upconversion luminescence enhancement is related to the thickness of doped Polymethylmethacrylate (PMMA) layer. Furthermore, due to the excited upconversion luminescence having high directionality, it is shown that the strong upconversion luminescence could be received at the specific angle.

Infrared to visible up-conversion luminescence of SrF2:Ho particles upon excitation of the 5I7 level of Ho3+ ions

The visible and near-infrared (NIR) up-conversion luminescence (UCL) of a concentration series of fluoride phosphors SrF2:Ho (CHo = 1.3, 3.5, 4.8, 7.4, 8.9, 10.8, 13.0, 13.6 mol.%) upon excitation of the 5I7 level of Ho3+ ions are presented. The dependences of the UCL intensity corresponding to the 5F3→5I8, 5S2(5F4)→5I8, 5F5→5I8, 5I4→5I8, 5F3→5I6, 5I5→5I8, 5F5→5I7, 5I6→5I8 transitions on the concentration of Ho3+ ions were revealed. The UCL energy yield, color coordinates, and correlated color temperature (CCT) values were estimated. The maximum values of UCL energy yields of 0.03% (380–780 nm) and 0.09% (380–1100 nm) were registered for SrF2:Ho (3.5 mol.%) sample. All studied fluoride phosphors are characterized by a red glow of UCL. This glow corresponds to CCT of 6711–7474 K upon incident power density of 28 W/cm2. The UCL mechanisms of SrF2:Ho phosphors were proposed. The SrF2:Ho phosphors can be used as laser beam viewers of the two-micron radiation of thulium and holmium commercial lasers.

Designing Er3+ Single-doped ternary sulfide for highly efficient upconversion luminescence under 1550 nm excitation

Optimizing the host lattice is the most efficient strategy to break through the intrinsic characteristic of low efficiency up-conversion luminescence (UCL). In principle, ternary sulfide, e.g. NaYS2, is an ideal UCL host matrix due to its low phonon energy and highly asymmetrical crystal structure. However, it was found that the low lying S2-→Yb3+ charge transfer state (CTS) existing in the ternary sulfide material severely quenches the UCL under 980 nm excitation, which generally employs Yb3+ ion as the conventional sensitizer. Herein, we design Er3+ single-doped NaYS2 phosphors for highly efficient UCL under 1550 nm excitation. This novel NaYS2:Er3+ phosphor excited at 1550 nm exhibits a 94-fold enhancement of UCL intensities compared to that of conventional NaYS2:Yb3+,Er3+ under 980 nm excitation. More encouragingly, compared to the commercial β-NaYF4:Yb3+,Er3+ phosphors, the UCL efficiency and brightness of NaYS2:Er3+ excited at 1550 nm are twice that of β-NaYF4:Yb3+,Er3+ excited at 980 nm. Such extraordinary efficient UCL is accomplished by taking advantages of the intrinsic low phonon energy (279 cm−1) of the NaYS2 host and the highly asymmetrical trigonal crystal system. Furthermore, in the Er3+ single-doped NaYS2 system, the S2-→Er3+ CTS lies at a high state of ≈34500 cm−1, which will not quench the efficient UCL from Er3+ ions. The large absorption cross-section at 4I13/2 energy level (high response to 1550 nm radiation) and long lifetime of the metastable state of 4I9/2 also contribute to the population of the emission levels (2H11/2/4S3/2). These findings provide a new class of host materials for achieving highly efficient UCL.

An efficient construction model of multi-fluorescence morphologies in oxyfluoride matrix

As the most common up-conversion (UC) activation center now, Er3+ can emit the blue, green and red light under the excitation of 980 nm. It has important meaning how to manipulate the emission wavelength in practical application. In our work, a series of excellent UC luminescence materials Y6O5F8: M3+ (M = Yb, Er, and Fe) are synthesized by the hydrothermal method. Under the condition of different pH, the prepared precursors exhibited different phases of YF3 and Y(OH)1.63F1.37 and various morphologies. The hydrogen bond guides a regular crystal growth process. With the change of pH, OH group could be selectively introduced into the host during this different crystal growth process. The structure change is likely to decrease the rigidity of this lattice and adjusted the cut-off phonon energies, and further influence the f-f transition of Er3+, selectively forming red emission in Y6O5F8: Yb3+, Er3+. The intensity of red UC luminescence is enhanced by 22 times via Fe3+ co-doping into the Y6O5F8: Yb3+, Er3+ crystalline lattice. The introduction of transition metal ions Fe3+, produces an excellent energy transfer from <2F7/2, 4T1g> (Yb3+-Fe3+ dimer) to energy levels of Er3+ as well as the distortion of the crystalline field symmetry. In addition to the enhancing luminescence effect, Fe ions also introduce magnetism from the hysteresis loop curve. The temperature-dependent UC emission of Y6O5F8: Yb3+, Er3+, Fe3+ display significant thermal coupling occurs with a higher absolute sensitivity. Based on this, the anti-fake and temperature-sensitive luminescent applications of this material are investigated in detail.