Upconversion Luminescence Mechanism Research Articles

Plasmon-enhanced up-conversion luminescence and oxygen vacancy defect-induced yellow light in annealed Cu8S5@SiO2@Er2O3 nanocomposites

Monodispersed Cu8S5 nanoparticles were successfully synthesized by modified hot-injection method, and Cu8S5@SiO2@Er2O3 core-shell particles were designed and prepared for up-conversion luminescence. Under the excitation of 980 nm laser, the local surface plasmon resonance of Cu8S5 nanoparticles coupled with annealed Er2O3 crystals to enhance the up-conversion luminescence of Cu8S5@SiO2@Er2O3 nanocomposites in the green and red emission bands, compared with that of SiO2@Er2O3 particles. After addition of Cu8S5 nanoparticles, the local near-field enhancement of Cu8S5@SiO2@Er2O3 nanocomposites was ~36-folds stronger than that of annealed Er2O3 crystals under 980 nm incident light, indicating that Cu8S5 nanoparticles have excellent potential for enhancing the up-conversion luminescence of rare earth elements. The generation of yellow light at ~610 nm was attributed to oxygen vacancy defects in annealed Er2O3. The formation mechanism of oxygen vacancy defects in annealed Er2O3 was proposed and investigated. Furthermore, the mechanism of up-conversion luminescence of Cu8S5@SiO2@Er2O3 composites and the electronic band structure of annealed Er2O3 crystals were also discussed.

Up-conversion luminescence and energy transfer mechanism in ZnTiO3: Er3+,Yb3+ phosphor

Er3+ and Yb3+ doped zinc titanate (ZnTiO3) was successfully synthesized using the conventional solid-state reaction method. X-ray diffraction confirmed crystallization of an ecandrewsite ZnTiO3 of an undoped sample, although impurity phases from the dopants were present in the doped and co-doped samples. The surface analysis showed a morphology composed of agglomerated irregular shaped particles. The energy band gap of ZnTiO3 was affected by the incorporation of different concentrations of rare-earth dopant ions. After irradiating the ZnTiO3:Er3+,Yb3+ phosphors with a 980 nm laser beam, the phosphor displayed up-converted photoluminescence emission in the visible range of the electromagnetic spectrum. The emission mostly consisted of green and red bands of Er3+ ions with peaks located at 527, 545 and 665 nm. Co-doping with Yb3+ ions proved effective in enhancing the luminescence intensity of the Er3+ ion emission, through an energy transfer mechanism.

Study on the Upconversion Luminescence Mechanism of Tegtragonal LiYF4: RE with Sublattice Energy Cluster Construction and Crystal Field Manipulation

Study on the Upconversion Luminescence Mechanism of Tegtragonal LiYF₄: RE with Sublattice Energy Cluster Construction and Crystal Field Manipulation

The construction of sublattice level energy cluster for promoting UV upconversion emission in tetragonal LiYF4

The preparation of high performance upconversion luminescence materials with stronger shortwave emissions is still a challenge. In this work, the feature of hexagon circles sublattice structure of tetragonal LiYF4 was revealed, and the sublattice level energy clusters of 4 Yb3+-1Tm3+ were constructed by the substitution of 70 mol% Yb3+ for Y3+ in tetragonal LiYF4 matrix. The sensitizing ions concentration quenching was inhibited by the hexagon circles sublattice structure, and the upconversion luminescence was dramatically enhanced, especially, the UV band emission was enhanced about 20 times and the intensity ratio of UV to blue emissions was improved about 10 folds under the excitation power density of 0.230 W/cm2. Photon numbers of upconversion emissions obviously decreased with the increasing of sublattice level energy clusters that the upconversion process of three photons was changed to two steps of two photons process. The upconversion luminescence mechanism of sublattice energy cluster construction was system investigated. The material with high performance of UV and blue UC luminescence can be a well candidate for the applications of photodynamic therapy and photocatalytic, etc. The work may be an inspiration for high efficient UC luminescence materials design and preparation.

Up-conversion luminescence and optical temperature sensing properties in novel KBaY(MoO4)3:Yb3+,Er3+ materials for temperature sensors

In this article, a series of KBaY(MoO4)3:Yb3+,Er3+ (KBYMO:Yb3+,Er3+) materials with efficient up-conversion (UC) luminescence properties, were synthesized using a high-temperature solid-state reaction method. Upon 975 nm NIR laser excitation, characteristic Er3+ green emission bands around 529 and 550 nm and a feeble red band around 670 nm in KBYMO:Yb3+,Er3+ were observed, which corresponded to the Er3+ transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The UC luminescence mechanism in this kind of materials was analyzed to be a two-photon process and simultaneous energy transfer from Yb3+ to Er3+ ions. In order to explore its potential application in optical temperature sensor, the temperature-dependent behavior of a representative KBYMO:0.50 Yb3+,0.02Er3+ was investigated in detail. Based on fluorescent intensity ratio (FIR) technique, the calculated FIR values of I519/I550 in KBYMO:0.50 Yb3+,0.02Er3+ (250–460 K) were utilized as the original data. Therefore, the maximum absolute sensitivity Sa and relative sensitivity Sr were determined to be 0.01306 K-1 (420 K) and 1.80% K−1 (250 K), which can be comparable with reported optical thermometric materials before, respectively. The results suggest that as-prepared KBYMO:Yb3+,Er3+ can be promising candidates applied in optical temperature sensors with good sensitivities.

Impact of organic additives on synthesis and upconversion luminescence properties in Ln3+, Yb3+ (Ln3+=Er3+/Tm3+/Ho3+) doped CaSc2O4 nanocrystals via hydrothermal method

The influence of organic additives (Cit-3Na、EDTA、CTAB et al.) on structure, crystallinity, morphology and upconversion properties for CaSc2O4 nanocrystals was investigated by hydrothermal synthesis. Via adding organic additives, we obtain rod-like and square-like CaSc2O4 nanocrystals. The sample choosing Cit-3Na as organic additive exhibits the best uniformity, monodispersity, narrowest size distribution and strongest red emission, which is enhanced by a factor of 2.5, in comparison with no adding the organic additives. Simultaneously, the upconversion luminescence properties and mechanism of Ln3+/Yb3+ (Ln3+ = Er3+/Tm3+/Ho3+) doped CaSc2O4 nanocrystals were investigated by the spectra distribution and power dependence. The emitting color of CaSc2O4 nanocrystals can be tuned from blue to green and red. The results reveal that CaSc2O4: Er3+/Yb3+ nanocrystals is a perfect red emission material and CaSc2O4 is an ideal host for upconversion luminescence.

Structure design and modulation of dual-wavelength sensitive upconversion luminescence in RE2MoO6:Er3+/Yb3+ materials

A series of RE2MoO6: 2%Er3+, 15%Yb3+ (RE = Y, Pr, Nd, Sm, Eu, Gd, Dy, and Lu) nanoparticles were prepared by citric acid-assisted sol–gel method. The upconversion luminescence (UCL) properties of block-shaped Gd2MoO6: 2%Er3+, 15%Yb3+ were the best among the materials obtained. In addition, the UCL properties of the investigated systems by two strategies could be further improved. Modulation of the crystal structure could be achieved by the substitution of rare earth ions in matrix lattice. The UC emission intensity of Gd2MoO6 doped with Y3+ (40%) was enhanced about 2.27 (2.52) more times than that of Y3+-absent samples excited at 980 nm (1550 nm). Secondly, dual wavelength was used as the excitation wavelength simultaneously: The green UCL intensity of RE2MoO6: 2%Er3+, 15%Yb3+ was almost not changed, while the red UCL intensity was enhanced compared to the sum of the red UCL intensities excited by 980 nm and 1550 nm, respectively. The UCL mechanism excited by dual wavelength was investigated in detail, in which the two co-operative excitation processes were presented.

High luminescent TiO2-Yb2O3: Er, Li complex nano spherical upconversion phosphor prepared by a hydrothermally treatment

Green upconversion (UC) luminescent spherical TiO2-Yb2O3: Er, Li complex nanocrystals (about 62 nm) were hydrothermally prepared at 120 °C for 6 h then annealed at 800 °C for 4 h. The prepared TiO2-Yb2O3: Er, Li complex nanocrystal are anatase titanium dioxide and cubic ytterbium oxide complex structure. We compared the UC luminescence of samples with the Er concentration when fixed the Yb and Li at 10% and 20%, respectively. All samples showed UC emission peaks near 560, 660 and 845 nm. When the doping concentration of Er was 1.5%, the strongest green UC emission was achieved. The bright green light is observed by the naked eye under lighting conditions. Doping the appropriate proportion of Er,Yb and Li, using suitable process to form a complex to reduce phonon energy also obtained strong UC luminescent nanoparticles. The effective way is extended the effective energy transfer from Yb3+ to Er3+ as well as reduced the non-radiative decay. The UC luminescence mechanism was discussed.

Low-Temperature Solid-State Synthesis and Upconversion Luminescence Properties in (Na/Li)Bi(MoO4)2:Yb3+,Er3+ and Color Tuning in (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ Phosphors.

In this Article, we reported the synthesis and the upconversion luminescence (UCL) properties of a series of novel (Na/Li)Bi(MoO4)2:Yb3+,Er3+ [(N/L)BMO:Yb3+,Er3+] and (Na/Li)Bi(MoO4)2:Yb3+,Ho3+,Ce3+ [(N/L)BMO:Yb3+,Ho3+,Ce3+] phosphors. X-ray diffraction patterns and Rietveld refinements for several representative samples indicated the pure phase of as-prepared samples. The Yb3+,Er3+ codoped (N/L)BMO presented bright green luminescence under 975 nm laser excitation with UCL spectra showing two main green bands around 529 nm (Er3+, 2H11/2 → 4I15/2) and 551 nm (Er3+, 4S3/2 → 4I15/2), in addition to a very weak one at 655 nm (Er3+, 4F9/2 → 4I15/2). The (N/L)BMO:Yb3+,Ho3+ mainly showed a green band around 544 nm (5S2,5F4 → 5I8) and a red band around 654 nm (5F5 → 5I8) upon 975 nm laser excitation. With increasing Yb3+ concentrations in (N/L)BMO:Yb3+,0.01Ho3+, the red/green ratios decreased monotonously corresponding to the emission color variation from light red to light yellow. Both UCL mechanisms of Yb3+,Er3+ and Yb3+,Ho3+ were determined to be two-phonons absorption processes in (N/L)BMO:Yb3+,Er3+/Ho3+. The Ce3+ ions were introduced into Yb3+,Ho3+ codoped (N/L)BMO to show the color tuning from light yellow to light red originating from the cross relaxation processes of (CR1) Ho3+ (5F4,5S2) + Ce3+ (2F5/2) → Ho3+ (5F5) + Ce3+ (2F7/2) and (CR2) Ho3+(5I6) + Ce3+ (2F5/2) → Ho3+ (5I7) + Ce3+ (2F7/2), which is based on the energy matching of Ce3+2F7/2-2F5/2 level pairs with Ho3+5I6-5I7 and 5F4,5S2-5F5 level pairs and confirmed by the decay times. These results suggest good UCL properties of (N/L)BMO:Yb3+, Er3+ and (N/L)BMO:Yb3+, Ho3+, Ce3+ materials, and color modulation is easily controlled by varying Yb3+ concentration and a cross relaxation process between Ce3+ and Ho3+, which provides efficient methods to regulate the emission color of UCL phosphors.

Up-conversion photoluminescence properties and energy transfer process of Ho3+,Yb3+ Co-doped BaY2F8 fine fibers

An intermediate product was obtained by sintering PVP/[Ba(CH3COO)2+Y(NO3)3+Ho(NO3)3+Yb(NO3)3] fine fibers prepared by electrospinning. The Ho3+,Yb3+:BaY2F8 fine fibers were obtained by sintering the above products using a double-crucible reduction atmosphere fluorination technology. X-ray diffraction data analysis showed that pure monoclinic phase of Ho3+,Yb3+:BaY2F8 fine fibers was C2/m space group. Scanning electron microscopy (SEM) was used to test the morphology, indicating the size of the fine fibers is near 269 nm. By analyzing the up-conversion fluorescence spectrum, strong green and weak red up-conversion radiation at 536 nm and 658 nm were obtained with the optimal doping concentrations of Ho3+ and Yb3+ ions of 1% and 8%, respectively. The up-conversion luminescence mechanism of Ho3+,Yb3+:BaY2F8 fine fibers and the fluorescence lifetime at 536 nm have also been studied in detail.

Red upconversion luminescence (UCL) properties in one-dimensional Yb2Ti2O7:Er nanofibers via an electrospinning route

The upconversion luminescence (UCL) nanofibers with low dimensional structure have attracted increasing attention in recent years. It is known that oxides based UCL family possesses many merits such as higher stability and lower cost. Consequently, it is of great importance to study the UCL emission in one dimensional structured oxides. Here, we demonstrated that the one-dimension (1D) nanofibers were successfully fabricated via an electrospinning route and the upconversion emissions were realized in cubic pyrochlore Yb2Ti2O7:Er nanofibers. The crystal phase, morphology, crystal structure were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscope. The red color can be observed by the naked eye under 980 nm excitation. We proposed a UCL mechanism based on experiments, which revealed that the green bands corresponding to Er3+ ion transitions 4H11/2-4I15/2, 4S3/2-4I15/2 were suppressed, while the red band corresponding to the transition 4F9/2-4I15/2 became dominant. The enhanced red emission can be ascribed to the resonant energy transfer of Er3+ ions caused by the host Yb3+. This work paved the way for further studies on 1D nanofibers of cubic pyrochlore as well as their UCL applications.

Wide-range thermometry and up-conversion luminescence of Ca5(PO4)3F:Yb3+/Er3+ transparent glass ceramics

Ca5(PO4)3F:Yb3+/Er3+ glass ceramics (GCs) were successfully manufactured via traditional controlled crystallization method. The structural, optical and up-conversion (UC) illuminant properties were systemically investigated by XRD, TEM, HRTEM, fluorescence spectra and luminescence lifetime measurements. The results show that Ca5(PO4)3F:Yb3+/Er3+ nanocrystals has been precipitated from the precursor glass matrix and the UC luminescence mechanism of PG and GC660 is two-photon process. The enhanced UC emission intensity and extended lifetime of Er3+ is observed in the GCs. Using the temperature dependent fluorescence intensity ratio (FIR) of thermally coupled emitting states (4S3/2, 2H11/2) as thermometric index, Ca5(PO4)3F:Yb3+/Er3+ GCs present wide temperature-sensing range (298–798 K) and high absolute sensitivity (51.9 × 10−4 K−1 at 600 K). This finding suggests that Ca5(PO4)3F:Yb3+/Er3+GC materials are promising in optical temperature measurement field.

Preparation and photoluminescence enhancement of Au nanoparticles with ultra‐broad plasmonic absorption in glasses

AbstractThe metal nanoparticles with ultra‐broad localized surface plasmonic resonance (LSPR) absorption have been widely used to enhance the up conversion luminescence (UCL) of rare‐earth doped nanoparticles. However, there have been no reports on the preparation of metal nanoparticles with the ultra‐broad LSPR in the glasses. In this work, the gold nanoparticles with the ultra‐broad LSPR were prepared for the first time in the rare‐earth doped tellurite glasses by the high‐temperature melting method, and the influence of ultra‐broad LSPR on the UCL of Er3+–Yb3+ and Er3+–Yb3+–Nd3+ co‐doped tellurite glasses was investigated upon 980 and 808 nm excitation, respectively. With the precipitation of the Au NPs, about seven and 12‐fold enhancements were obtained for the green and red UCL of Er3+–Yb3+ co‐doped tellurite glasses excited at 980 nm, respectively, and about 5.9 and sevenfold enhancements were observed for the green and red UCL of Er3+–Yb3+–Nd3+ co‐doped tellurite glasses excited at 808 nm, respectively. The UCL mechanism related to UCL enhancement was confirmed. The results demonstrated that the enhanced excitation field and the increasing rate of radiative decay were responsible for the enhancement of UCL.

Near-Infrared Upconversion Luminescence and Bioimaging In Vivo Based on Quantum Dots.

Recently, upconversion luminescence (UCL) has been widely applied in bioimaging due to its low autofluorescence and high contrast. However, a relatively high power density is still needed in conventional UCL bioimaging. In the present study, an ultralow power density light, as low as 0.06 mW cm−2, is applied as an excitation source for UCL bioimaging with PbS/CdS/ZnS quantum dots (UCL‐QDs) as probes. The speculated UCL mechanism is a phonon‐assisted single‐photon process, and the relative quantum yield is up to 4.6%. As determined by continuous irradiation with a 980 nm laser, the UCL‐QDs show excellent photostability. Furthermore, UCL‐QDs‐based probe is applied in tumor, blood vessel, and lymph node bioimaging excited with an eye‐safe low‐power light‐emitting diode light in a nude mouse with few heat effects.

Synthesis, characterization and upconversion luminescence of core-shell nanocomposites NaYF4: Er/Yb@SiO2@Ag/Au

The improvement in the upconversion (UC) luminescence due to the surface plasmonic properties of precious metals is an effective mode to increase UC luminescence efficiency. In the present research work, pure hexagonal-phase NaYF4: Yb, Er UC nanocrystals were prepared via a reverse micro emulsion method. A single-step method was adopted to change the hydrophobic surfaces of the as-prepared NaYF4: Yb, Er nanocrystals. After the surface modification, Au/Ag nanoparticles were decorated on the surfaces of NaYF4:Yb, Er nanocrystals. The structural analysis and composition of the nanocomposites were studied in details. The XRD pattern indicated the formation of the hexagonal structure of NaYF4 crystals. The decorated UC nanocrystals exhibited a prominent UC emission in green and red bands under 980 nm laser excitation due to normal two-photon UC process. The UC intensity increased by ∼3 times than the uncoated samples. The enhancement mechanism of UC luminescence was investigated in details.

Preparation of PbF2:Ho3+, Er3+, Yb3+ phosphors and its multi-wavelength sensitive upconversion luminescence mechanism

In this paper, PbF2: Ho3+, Er3+, Yb3+ phosphors are prepared by a high-temperature solid-state method. The crystal structure acquired by X ray powder diffractometer shows that the resultant phosphor is a pure cubic PbF2 crystal. The upconversion (UC) emission spectra of samples are performed by a fluorescence spectrophotometer coupled with lasers of 980 nm, 1064 nm and 1550 nm, presenting the green emission in the range of 541∼548 nm and red emission in the range of 653–667 nm, corresponding to the excitation path: Ho3+: 4F9/2→4I15/2, Er3+: 4S3/2→4I15/2, Er3+: 4F9/2→4I15/2 and Ho3+: 5F5→5I8. Finally, the UC luminescence mechanism is analyzed under excitation of different wavelengths. The result shows that the phosphors have a promising prospect for application in anti-counterfeiting technologies and solar cell field.

Study on Upconversion and Thermal Properties of Tm3+/Yb3+ Co-Doped La₂O₃-Nb₂O₅-Ta₂O₅ Glasses.

The effect of Yb3+ ions on upconversion luminescence and thermal properties of Tm3+/Yb3+ co-doped La2O3-Nb2O5-Ta2O5 glasses has been studied. Glass transition temperature is around 740 °C, indicating high thermal stability. The effect of Yb3+ ions on the thermal stability is not obvious. Both the glass forming ability and the upconversion luminescence first increase and then decrease with the increase of Yb3+ ions. The glasses perform low glass forming ability with ΔT around 55 °C. Blue and red emissions centered around 477, 651, and 706 nm are obtained at the excitation of 976 nm laser. The upconversion luminescence mechanism is energy transfer from Yb3+ to Tm3+ mixed with two- and three- photon processes. The thermal kinetic Differential Thermal Analysis (DTA)-analysis indicates that the average activation energy first increases and then decreases with the increase of Yb3+ ions. This result can be introduced in order to improve upconversion luminescence of glasses by crystallization in the future. Tm3+/Yb3+ co-doped La2O3-Nb2O5-Ta2O5 glasses with good upconversion and thermal properties show promising applications in solid-state laser, optical temperature sensing.

Preparation and Properties of Rare-earth-doped Na2Ca3Si2O8 and BaZrSi3O9 Matrix Luminescent Materials

To achieve higher quality temperature measurement, this paper studies the rare-earth-doped Na2Ca3Si2O8 and BaZrSi3O9 matrix luminescent materials. The paper mainly adopts sol-gel method to prepare luminescent material in the form of thin film and powder. By comparing the thermodynamic reaction of the two materials and their respective properties, the differences between the two are further distinguished. The results illustrate the temperature-dependent up-conversion luminescence mechanism of thin film and explain the relationship between the up-conversion luminescence intensity and temperature. The results show that more accurate temperature measurements can be achieved.

Temperature sensing behavior in Yb3+–Tb3+ and Eu3+ doped Ca2Gd8(SiO4)6O2 phosphors based on upconversion and downshifting luminescence

To develop new phosphor materials for optical temperature sensing application, a series of Yb3+–Tb3+ and Eu3+ doped Ca2Gd8(SiO4)6O2 (CGS) phosphors were designed by solid-state reaction method. Upon 980 nm excitation, the green emission of Tb3+ was observed in the CGS:0.8Yb3+, xTb3+ (0.08 ≤ x ≤ 1.2) phosphors, which could be mainly owing to the cooperative energy transfer from Yb3+ to Tb3+. The corresponding upconversion (UC) luminescence mechanism was studied by using the dependence of UC emission intensity on excitation powder. The temperature-dependence indicates that the ratio of the Tb3+ emission intensities of I5D4 and I5D3 changes with temperature, which shows a linear relationship. The high absolute sensitivity was achieved to be about 0.431 K−1. Upon 463 nm excitation, the Eu3+ 5D0,1–7FJ transitions were found in the Eu3+-activated CGS. The investigation on temperature-dependence reveals that with increasing temperature the intensities of 5D0–7FJ transitions decrease but those of 5D1–7FJ transitions increase gradually, owing to the thermally coupled 5D0 and 5D1 levels. The fluorescence lifetime based temperature sensing properties was studied in this sample.

Fabrication and characterization of Er, Nd codoped Y2O3 transparent ceramic: A dual mode photoluminescence emitter

The transparent Er, Nd co-doped Y2O3 ceramics with transparency ∼78% (in 500–2000 nm range without Fresnel's correction) were fabricated successfully. It involved nanoparticle synthesis by coprecipitation method and sintering of pellets under high vacuum condition. The crystalline phase, particle size and element composition were confirmed by X-ray diffraction, scanning electron microscope, energy dispersive X-ray fluorescence techniques, respectively. The upconversion luminescence mechanisms involving energy transfer and non-radiative relaxation were analyzed. It is expected that, the result evolved from this study will provide better understanding of upconversion mechanism involved in Er, Nd codoped host material. The emission at both 563 nm (Er3+:4S3/2 → 4I15/2) and 1064 nm (Nd3+:4F3/2 → 4I9/2) on 822 nm (Nd3+:4I9/2 → 4F5/2) excitation proves potential of the ceramic material for dual mode efficient emitter at room temperature.