Upconversion Luminescence Performance Research Articles

Optimization of upconversion luminescence performance and temperature sensing characteristics of Sr0.37Ba0.50Al2Si2O8:Ho3+, Yb3+ phosphors based on a cation substitution strategy

Upconversion luminescent (UCL) materials have broad application prospects in the field of temperature sensing; thus, improving the luminescence performance and temperature measurement sensitivity of upconversion phosphors is highly important. In this study, SrAl2Si2O8 with good thermal stability was doped with Ho3+ and Yb3+, and the optimal concentration was determined to be SrAl2Si2O8:1%Ho3+, 12%Yb3+ (in mole fraction). A series of (Sr0.87‒xBax)Al2Si2O8:1%Ho3+, 12%Yb3+ phosphor samples was prepared by using a cationic substitution strategy and further doping Ba2+ to replace the Sr2+ lattice in the matrix. The results show that the introduction of Ba2+ effectively replaces Sr2+ and significantly increases the upconversion fluorescence emission intensity of SrAl2Si2O8:1%Ho3+, 12%Yb3+ by approximately 2.9 times. The temperature sensing properties of SrAl2Si2O8:1%Ho3+, 12%Yb3+ and Sr0.37Ba0.50Al2Si2O8:1%Ho3+, 12%Yb3+ were investigated. The Ho3+-based 5F5 and 5S2/5F4 nonthermal coupled energy level fluorescence intensity ratio (FIR) techniques in the Ba0.37Sr0.50Al2Si2O8:1%Ho3+, 12%Yb3+ phosphors show a maximum temperature measurement absolute sensitivity of 4.32%/K at 573 K and a maximum relative sensitivity of 1.08%/K at 373 K; these values are 5.8 and 3.2 times greater, respectively, than that of the non-Ba2+-doped SrAl2Si2O8:1%Ho3+, 12%Yb3+ phosphor. These results not only confirm the effectiveness of the cation substitution strategy in enhancing the upconversion luminescence performance and temperature sensing characteristics but also provide a scientific basis for the design of high-performance optical temperature sensors.

Improved thermometry sensitivity of red-emitting SrGd2O4:Er3+,Yb3+ phosphors using novel NTCL-FIR technology based on 2H11/2 and 4F9/2

In this work, the upconversion luminescence (UCL) and temperature-sensing properties of SrGd2O4 phosphors doped with Er3+, Yb3+ were investigated. The UCL performance was studied by adjusting the doping concentrations of Er3+, Yb3+. It can be found that the intensity of red UCL is effectively improved by doping Yb3+ ions. The band structures of SrGd2O4, SrGd2O4:5 mol%Er3+, and SrGd2O4:5 mol%Er3+,15 mol%Yb3+ were calculated using the density functional theory (DFT) to verify the experimental results. The thermal sensitivity of SrGd2O4:5 mol%Er3+,15 mol%Yb3+ phosphors was studied using the novel fluorescence intensity ratio of non-thermally coupled energy levels (NTCL-FIR) technique based on the 2H11/2 and 4F9/2 energy levels. The analytical results reveal that the maximum values of Sr are 1.69%/K (300 K), 1.18%/K (300 K) and 1.47%/K (300 K) respectively under 915, 980 and 1550 nm excitations. The Sr values of novel NTCL-FIR are compared with that of thermal coupling of energy level (TCL) and other studies in the same field. The results show that the thermometry sensitivity of red-emitting UCL materials can be enhanced by using the novel NTCL-FIR technique. In addition, the intense red UCL of SrGd2O4:Er3+,Yb3+ phosphors have the advantage of deeply penetrating biological tissues. Therefore, the combination of novel NTCL-FIR and red-emitting SrGd2O4:Er3+,Yb3+ phosphors could be conducive to temperature monitoring in vivo.

Effect of microwave heat-treatment on up-conversion luminescence of Er3+/Yb3+ co-doped NaYF4 oxy-fluoride glass-ceramics

The microscopic properties of fluoride grains are known to play critical roles in the up-conversion luminescence properties of phosphors carrying rare-earth-based luminescence centers. To study the effect of different heating methods during preparation on the microstructure and up-conversion luminescence performance of oxy-fluoride glass-ceramics, we synthesized Er3+/Yb3+ co-doped NaYF4 nanocrystals containing transparent glass-ceramics by microwave heat-treatment and the normally heating methods. We characterized the internal structure of glass-ceramics by X-ray diffraction, transmission electron microscopy, mid-infrared spectroscopy, and Raman spectroscopy. While glass-ceramics samples prepared by both methods have extremely high optical transmittance similar to that of a glass, the microwave heat-treatment promoted faster grain growth rate, the glass-ceramics sample had better crystallinity and much improved up-conversion luminescence intensity compared to the sample obtained by the normally heating method.

Full-Spectrum Utilization of ZIF-67/Ag NPs/NaYF4:Yb,Er Photocatalysts for Efficient Degradation of Sulfadiazine: Upconversion Mechanism and DFT Calculation.

In this work, novel ternary composite ZIF-67/Ag NPs/NaYF4:Yb,Er is synthesized by solvothermal method. The photocatalytic activity of the composite is evaluated by sulfadiazine (SDZ) degradation under simulated sunlight. High elimination efficiency of the composite is 95.4% in 180min with good reusability and stability. The active species (h+, ·O2 - and ·OH) are identified. The attack sites and degradation process of SDZ are deeply investigated based on theoretical calculation and liquid chromatography-mass spectrometry analysis. The upconversion mechanism study shows that favorable photocatalytic effectiveness is attributed to the full utilization of sunlight through the energy transfer upconversion process and fluorescence resonance energy transfer. Additionally, the composite is endowed with outstanding light-absorbing qualities and effective photogenerated electron-hole pair separation thanks to the localized surface plasmon resonance effect of Ag nanoparticles. This work can motivate further design of novel photocatalysts with upconversion luminescence performance, which are applied to the removal of sulphonamide antibiotics in the environment.

Molten Salt Synthesized CaTa4O11:Er3+/Yb3+ with Superior Upconversion Luminescence.

Low phonon tantalate-based phosphors with a layer structure are considered to have excellent upconversion luminescence (UCL) intensity, which could be reduced due to the existence of impure phase defects and inappropriate doped rare earth ions. To improve their UCL performance, we have prepared single-phase CaTa4O11:Er3+/Yb3+ samples by a molten salt synthesis (MSS) using KCl as the reaction medium and compared its UCL properties with counterparts made by a conventional solid-state reaction (SSR) in this study. We have demonstrated that the MSS samples have a much higher UCL intensity under 980 nm laser excitation than the SSR ones due to accurate replacement of Ca2+ sites by Er3+/Yb3+ in high-purity single-phase MSS samples. We have further enhanced the green UCL intensity of the MSS samples by 1.57 times via acid picking (AP). Under 980 nm laser excitation at a high powder density of 61.3 W/cm2, the green UCL intensity of the MSS-AP samples can reach 3.72 times that of the SSR-AP samples. For potential luminescence thermometry applications, the maximum absolute sensitivity (SA) of the MSS-AP samples reaches 0.01316 K-1 at 501 K based on the luminescence intensity ratio. This study shows that CaTa4O11:Er3+/Yb3+ phosphors prepared by the MSS method are single-phase samples with excellent pure green UCL as a suitable temperature sensing material.

Plasmon modulated luminescent modes of upconversion nanoparticle by coupling with AuNR@SiO2 nanostructure

Lanthanide-doped upconversion nanoparticles (UCNPs) can convert near-infrared light into visible light emission, and have attracted more and more interests due to their great potential in ultrasensitive biosensors. However, it is still a huge challenge to manipulate the intensity ratio between different emission lines and realize the modulated up-conversion. In this work, the upconversion luminescence performance of UCNPs was regulated by coupling with Au nanorod-silicon core–shell (AuNR@SiO2) nanostructures. By changing the thickness and surface charge of the silica shell, the influence of the thickness and surface charge on the energy transfer of the UCNPs was explored. It is expected that the up-conversion luminescence effect of this composite nanostructure regulated by plasmons can provide a basis for the extensive exploration of biological detection and sensing applications.

Bi2MoO6 nanoflower-like microsphere photocatalyst modified by boron doped carbon quantum dots: Improving the photocatalytic degradation performance of BPA in all directions

Bi-based semiconductor photocatalyst represented by Bi2MoO6 (BMO) has obvious advantages in the degradation of bisphenol A (BPA), but three prominent problems that restrict the improvement of photocatalytic performance, namely, insufficient solar absorption, less active sites and serious photogenerated carrier recombination, need to be solved urgently. For this reason, we specially designed a simple structure of B-doped carbon quantum dots (BCQDs) modified BMO nanoflower-like microsphere composite to improve the photocatalytic performance of the system from the above three dimensions. The optimized BCQDs/BMO sample completely degraded BPA within 120 min under simulated sunlight, corresponding to an apparent constant of 0.03453 min−1, while the control sample of CQDs/BMO without B doping only degraded about 84 % of BPA within 160 min, with an apparent coefficient of 0.01138 min−1. Even after filtering out UV components below 400 nm, the degradation performance of the optimal composite catalyst did not decrease. The improved catalytic performance comes from the excellent up-conversion luminescence performance and good electron storage capacity of CQDs on the one hand, and the introduction of B on the other hand can adjust the surface structure of CQDs to generate more active sites and functional interfaces to further promote the catalytic reaction. Free radical trapping and electron spin resonance (ESR) tests have shown that·OH and·O2- are the main active substances in the degradation of BPA. The current BCQDs/BMO catalysts, despite their simple structure, can simultaneously improve the catalytic performance from the three important aspects mentioned above, which will guide the design of others semiconductor based photocatalysts.

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.

Up-conversion luminescence performance of Yb3+, Er3+/Ho3+ co-doped Y2W3O12 phosphors

Up-conversion luminescence performance of Yb3+, Er3+/Ho3+ co-doped Y2W3O12 phosphors

Effect of local crystal field environment on luminous properties of Er3+/Yb3+-doped titanate upconversion luminescent materials

The upconversion luminescence performance is closely related to the local crystal field environment. However, it is challenging to achieve an ideal luminescence performance by local crystal structure engineering. In this work, four titanate upconversion luminescent materials with fixed elemental compositions were synthesized, which enabled systematic exploration effects of the local crystal field environment (local structure symmetry and interatomic distance) on the upconversion performance. When the effects of local structure symmetry and interatomic distance on upconversion performance were taken into account individually, it was not easy to precisely characterize how the local crystal field environment influenced the upconversion performance. Thus, to illustrate this issue, we established a mathematical model that can satisfactorily describe the variation trend of the red/green integrated intensity ratio in terms of the product of local crystal field intensity and interatomic distance. This finding provides an excellent theoretical basis for the design of luminescent materials with ideal upconversion performance.

Bright upconversion luminescence performance of Yb3+/Tm3+/Gd3+/Er3+ doped AWO4 (A=Sr or Ca) phosphor for optical temperature sensor

A series of AWO4 (A = Sr, Ca): Yb3+/Tm3+/Gd3+/Er3+ phosphors are successfully prepared by solid-state method. In comparison with the samples without Gd3+ ions, the UC emission intensity of CaWO4: 0.5 mol%Tm3+/1 mol%Yb3+/10 mol%Gd3+ sample has increased by 104 times (∼475 nm), 71 times (∼655 nm) and 23 times (∼795 nm) due to the shrink of the host lattice with the Gd3+ ions corporation. Based on the fluorescence intensity ratio (FIR) of non-thermal couple levels(non-TCLs), the temperature sensing characteristics are investigated for AWO4 (A = Sr, Ca): Yb3+/Tm3+/Gd3+/Er3+ phosphors. The maximum values of absolute sensitivity and relative sensitivity are 0.09356 K-1 and 1.499% K−1 for CaWO4: Yb3+/Tm3+/Gd3+/Er3+ phosphor. It indicates that the AWO4 (A = Sr, Ca): Yb3+/Tm3+/Gd3+/Er3+ phosphors can be applied to develop optical thermometry.

Novel BaY1-xGdxF5: Yb3+/Er3+/Bi3+ solid solution nanocrystals with enhanced upconversion luminescence and magnetism properties

Fluoride phosphors with enhanced upconversion luminescence performance and multi-functionalization are urgently explored for applications in modern bio-detection and medical imaging. Here, a series of BaY1-xGdxF5: Yb/Er/Bi (0 ≤ x ≤ 0.5) solid solution nanocrystals are designed and synthesized. The influence of Gd3+-doping concentration on microstructure, upconversion luminescence, and magnetic performances are deeply reported. XRD results demonstrate the formation of solid solution with cubic phase structure. With increasing Gd3+ concentration, the diffraction angle gradually shifts toward lower direction as a result of replacing Y3+ by Gd3+ with larger ionic radius. Microstructure results show that the size distribution is between 60 and 100 nm and reveal that Gd3+ facilitates the growth of crystal grains. Upon 980 nm excitation, the BaY1-xGdxF5: Yb/Er/Bi samples demonstrate two dominant green and red emissions of Er3+ at 546 nm and 658 nm, respectively. By substituting Y3+ with Gd3+, the characteristic green luminescence can efficiently lead to an obvious enhancement at x = 0.2. The detailed enhancement mechanism is presented. Besides, the obtained nanocrystals show excellent paramagnetism properties, and the magnetic magnitude is significantly enhanced with increasing Gd3+ concentration. These results indicate that the BaY1-xGdxF5: Yb/Er/Bi nanocrystals are promising three-mode probes with potential applications in medical imaging and disease diagnosis.

Up-conversion luminescence performance of Tm3+/Yb3+ co-doped strontium cerate phosphors

Tm3+/Yb3+ co-doped Sr2CeO4 phosphors were fabricated via a high-energy ball milling technique. The structural, morphological, and luminescence characteristics were analyzed by XRD technique, field emission scanning electron microscopy, and up-conversion luminescence spectra, respectively. The structural X-ray diffraction patterns indicate their orthorhombic structure. Under excitation at 975 nm, the up-conversion luminescence spectra of Sr2CeO4:Tm3+/Yb3+ samples with various concentrations of Yb3+ were observed. The phosphor containing 10 mol% Yb3+ ions exhibited optimal up-conversion luminescence. All the samples show emission peaks at 478, 652, and 801 nm, which are assigned to the 1G4 → 3H6, 1G4 → 3F4, and 3H4 → 3H6 transitions of Tm3+. A detailed analysis of the up-conversion mechanisms is proposed based on simplified energy level diagram. The results show that the Sr2CeO4:Tm3+/Yb3+ phosphor has potential application prospects in wide-range and light emitting devices.

Up-conversion luminescence performance and application of GdOF:Yb,Er porous spheres obtained by calcining NaGdF4:Yb,Er microcrystals

Precise tuning of the structure, luminescence intensity, and color of lanthanides-doped up-conversion (UC) micro/nanomaterials is essential for many applications. Herein, a porous material with enhanced UC emission was achieved by calcining the hexagonal phase NaGdF4:Yb,Er microrods synthesized by the hydrothermal method. Under excitation at 980 nm, compared to the as-synthesized NaGdF4:Yb,Er microcrystal, the 700 ℃ calcined products exhibit a single-band red UC luminescence and nearly two orders of luminescence enhancement. However, the XRD patterns of the calcined products are simultaneously consistent with the cubic phase NaGdF4 and rhombohedral phase GdOF, which makes the composition of calcined products be an open question. We have carefully designed and carried out some experiments, and then verified the GdOF identity of the calcined products. Interestingly, GdOF:Yb,Er porous spheres exhibit a greater loading capacity (0.25 g/g) of Cu-Cy photosensitizer than the as-synthesized NaGdF4:Yb,Er (0.12 g/g) microcrystals. Furthermore, after loading the photosensitizer, GdOF:Yb,Er porous spheres still emit a strong single-band red luminescence upon 980 nm excitation. These phosphors can also be used as security inks for printing luminescent patterns. This study provides a novel way towards the preparation of the GdOF:Yb,Er porous phosphors with a tremendous potential in drug loading, anti-counterfeiting and imaging applications.

Er3+ and Sr(Bi0.5Nb0.5)O3-modified (K0.5Na0.5)NbO3: A new transparent fluorescent ferroelectric ceramic with high light transmittance and good luminescence performance

In this work, (K 0.5 Na 0.5 )NbO 3 –Sr(Bi 0.5 Nb 0.5 )O 3 : x wt% Er 3+ ( x = 0.1–0.4) transparent fluorescent ferroelectric ceramics were prepared using traditional solid-phase method. By solid solution of the second component Sr(Bi 0.5 Nb 0.5 )O 3 (SBN) and doped rare earth Er 3+ to modify (K 0.5 Na 0.5 )O 3 (KNN), it was successfully prepared with good luminescence performance while maintaining ceramic samples with excellent light transmittance. Results show that the representative 0.94(K 0.5 Na 0.5 )NbO 3 -0.06Sr(Bi 0.5 Nb 0.5 )O 3 : 0.1 wt%Er 3+ ceramic sample has a light transmittance of 80.25% in the near-infrared band (1100 nm). Meanwhile, in the visible light band (780 nm), the light transmittance is maintained at 71.95%. At the same time, the ceramic sample has good up-conversion luminescence performance, with two green light emissions and one red light emission at 525, 550 and 665 nm. The SEM photos show that the crystal grain size of the ceramic sample reaches the nanometer level with a fine and dense microstructure. The XRD pattern shows that the ceramic sample is in the pseudo cubic phase structure with the weakest optical anisotropy. In addition, the introduction of Bi 3+ makes the ceramic samples significantly suppress P r while maintaining a high P max , the ceramic samples have certain ferroelectric properties and good energy storage potential. This work has prepared an excellent multifunctional material, which provides helpful references for the development of opto-electronic materials.

Effect of excitation mode on the upconversion luminescence of β-NaYF4:Yb/Er nanocrystals

Upconversion nanoparticles (UCNPs) with multi-color emissions have been studied extensively owing to their potential applications in diverse research fields. The upconversion luminescence (UCL) of UCNPs is greatly affected by the excitation mode or intensity of NIR laser. Herein, the effect of excitation mode (continuous wave and pulsed excitation) on the UCL and modulation mechanism of β-NaYF4:Yb/Er nanocrystals were investigated. In this Yb3+-Er3+ co-doped nanocrystals, temporally red emission was dramatically realized by employing pulsed excitation mode. As a result, bright red color luminescence was output in β-NaYbF4:2%Er3+ nanocrystals. Besides, pulsed excitation can partially eliminate the concentration quenching effect, enhancing the optimal Yb3+ doping ratio from 20% to 50%. Excitation mode would change the dynamic balance of excitation energy transfer processes, which eventually leads to the variation of UCL of β-NaYF4:Yb/Er. These fantastic insights may open up new pathways to efficiently tailor upconversion luminescence performance in favor of further development of applications.

Enhancement of the up-conversion luminescence performance of Ho3+-doped 0.825K0.5Na0.5NbO3-0.175Sr(Yb0.5Nb0.5)O3 transparent ceramics by polarization

Enhancement of the up-conversion luminescence performance of Ho3+-doped 0.825K0.5Na0.5NbO3-0.175Sr(Yb0.5Nb0.5)O3 transparent ceramics by polarization

Structural design and synthesis of new MOO3-x interlayer bi-functional nanomaterials for enhanced up-conversion luminescence properties

A novel imaging materials based on bi-functional Fe3O4@MOO3-x@YF3:Yb/Er nanoparticles (NPs) with strong up-conversion luminescence and magnetic properties was designed and synthesized by inlaying MOO3-x with localized surface plasmon resonance (LSPR) and ferromagnetic property in the bi-functional Fe3O4@YF3:Yb/Er NPs. The morphology, structure and properties of Fe3O4@MOO3-x@YF3:Yb/Er NPs are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), photoluminescence (PL) spectra, UV–Vis-NIR spectrophotometer and superconducting quantum interference devices (SQUID). It was found that the experimental conditions (reaction temperature, reaction time, the mass ratio of core:shell and oxygen pressure in heat treatment) have a certain effect on the oxygen defect concentration of the MOO3-x interlayer. XRD also showed the crystal structure of Fe3O4, Fe3O4@MOO3-x and Fe3O4@MOO3-x@YF3:Yb/Er NPs. The SEM and TEM results showed that the average grain size of the prepared NPs were 200 nm. The SQUID and PL results showed that the Fe3O4@MOO3-x@YF3:Yb/Er NPs have stronger magnetism (14.3 emu/g) and excellent up-conversion luminescence performance (the emission peak at 525 nm is nearly 20 times higher than the corresponding emission intensity of the Fe3O4@YF3:Yb/Er). The Fe3O4@MOO3-x@YF3:Yb/Er NPs can be easily used to magnetic resonance and fluorescence dual-mode image-guided visual delivery drug and also increase the accurate diagnosis and treatment effect of malignant tumor.

Preparation and luminescence properties of ZnWO4: Tb3+/Yb3+ glass ceramics

Tb3+/Yb3+ co-doped glass ceramics containing ZnWO4 crystals were prepared by melting crystallization method. The effects of Tb3+ and Yb3+ doping on the crystal phase and luminescence properties of glass ceramics were studied. The XRD analysis confirmed the existence of ZnWO4 crystals in glass ceramics, with the increase of Tb3+ doping concentration, the crystal phase changed to Na0.5Tb0.5WO4. The effect of heat treatment time and doping concentration of Tb3+ on the luminescence performance of the glass ceramics were studied to determine the optimal doping concentration of Tb3+. When the concentration of Tb2O3 is 0.1 mol%, with the increase of Yb2O3 doping concentration, the crystal phase of glass ceramics changes from ZnWO4 to Na0.5Yb0.5WO4. The up-conversion luminescence performance of Tb3+/Yb3+ co-doped glass ceramics was studied, and the optimal doping concentration ratio between Tb2O3 and Yb2O3 is determined to be 1:7.

Enhancement of field-induced strain and bright upconversion luminescence in BNT-based multifunctional ceramics

In this work, a multifunctional lead-free (Bi0.5Na0.5)0.945Ba0.065Ti(1−x)(Fe0.5Sb0.5)xO3-0.005Er (BNBT-Er-xFS) ferroelectric material was prepared through the solid-state method, which has a large reversible field-induced strain of 0.465% (under an moderate electric field of 65 kV/cm) with a high normalized strain d33* (Smax/Emax) of 713 pm/V. Besides the excellent strain properties, this system also exhibits a bright green upconversion emission under excitation of 980 nm due to the luminescence characteristic of Er3+ ion. Moreover, the upconversion luminescence performance of BNBT-Er-xFS is enhanced with the (Fe0.5Sb0.5)4+ doping. At x = 0.0075, sample exhibited the strongest upconversion luminescence. As a multifunctional material, the BNBT-Er-xFS system is expected to be used in multifunctional electronic devices due to its excellent electrical and photoluminescence performance.