Upconversion Emission Of Yb3 Research Articles

Up-conversion emission of Yb3+/Tm3+-activated SrNb2O6 lead-free glass-ceramics for optical temperature sensors

The development of fluorescent materials with excellent thermal stability and high-temperature sensitivity is urgently needed to meet the rapidly growing temperature sensors. In this paper, the SrO-SrF2-Nb2O5-Al2O3-B2O3-SiO2-Yb2O3-Tm2O3 glasses were fabricated by high-temperature melting method. And the glass-ceramic with the optimal concentration of 4.0Yb3+/0.1Tm3+ was obtained after heat treatment of 800 °C for 30 min. Only the nanocrystalline SrNb2O6 crystal phase with a tetragonal structure precipitated from the glass matrix. The as-prepared glass-ceramic material produced intense blue light emission and excellent thermal cyclic stability. Utilizing the fluorescence intensity ratio technique, the glass-ceramic material showed the supreme relative sensitivity of 2.63 %K−1 at 298 K using thermally coupled energy levels (TCELs) and the highest absolute sensitivity of 22.10 %K−1 at 598 K employing non-TCELs. These findings show that Yb3+/Tm3+- doped SrNb2O6 glass-ceramic material is a promising candidate for optical sensor application.

Color Tuning and Optical Temperature Sensing Properties of Upconversion Emission in Yb3+/Er3+/Tm3+Doped Boro-Zinctellurite Glasses

Zinc borotellurite (B2O3/BaO/ZnO/TeO2) glasses co-doped with Tm3+/Yb3+, Er3+/Yb3+ and tri-doped Tm3+/Er3+/Yb3+ were prepared using the traditional melt quenching method. Optical absorption spectra were measured in the wavelength range of 350 nm-1100 nm at room temperature. The optical bandgap (Eg) and Urbach energy were calculated from Tauc’s plot. Blue and green emissions that can be seen by the naked eye were generated under 975 nm laser light excitation in doped Tm3+/Yb3+ and Er3+/Yb3+ doped glasses. Shifts in both blue and green color coordinates were seen as the excitation power density increased from 0.5 to 15.1 W cm−2. A white light generation was generated in glass doped with Tm3+/Er3+/Yb3+ ions, although a noticeable shift was not observed in both blue and green color coordinates for the same excitation power density range. Temperature sensing properties were investigated using the fluorescence intensity ratio of upconversion green emissions from the two thermally coupled 2H11/2 and 4S3/2 levels of Er3+ ions between 304 K and 443 K. The maximum sensitivity of the glasses doped with Er3+ and Er3+/Yb3+ were found to be 7.2 × 10−3 K−1 and 1.2 × 10−2 K−1 at 429 K, respectively.

Optical thermometry based on upconversion emission of Yb3+/Er3+ codoped bismuth titanate microcrystals

Optical thermometry has drawn great attention due to its sensitive and noncontact properties. Herein, Yb3+/Er3+ codoped Bi4Ti3O12 phosphor microcrystals have been synthesized by solid phase reaction for optical temperature sensing. The phase, microscopic structure and morphology of the prepared sample have been studied by the X-ray diffraction, transmission electron microscopy, etc. The process of upconversion emission has been researched with different environmental temperature and excitation power under 980 nm laser excitation. Meanwhile, the temperature sensing nature of the as-prepared microcrystals has been investigated based on the luminescence intensity ratio of two thermally coupled energy levels (Er3+:2H11/2, 4S3/2). The excitation laser power density is 3.95 mW/mm2, and the absolute sensitivity reaches 0.0046 K-1. The result demonstrates potential of the Bi4Ti3O12:Yb3+/Er3+ microcrystals in making optical sensing device under low excitation power density.

The color tunability and mechanism of upconversion emissions in Yb3+ and Er3+ co-doped Y2Ce2O7 phosphors

Y2Ce2O7 powders doped with different Yb3+ and Er3+ concentrations were synthesized via the sol-gel method. The structure and upconversion properties were investigated. The results indicated that a single phase was obtained and that the structure was cubic. The green and red upconversion emissions were detected with excitation at 980nm, and the emission intensities could be tuned by the Yb3+ and Er3+ concentrations. The mechanism of the upconversion process was evaluated on the basis of the emission intensities and lifetimes of the 4S3/2, 4F9/2 and 4I13/2 levels. The results demonstrated that cross-relaxation was responsible for the dependence of green and red upconversion emissions on the dopant concentration.

Preparation, Structure, and Up‐Conversion Luminescence of Yb3+/Er3+ Codoped SrIn2O4 Phosphors

SrIn2O4, which shows lower phonon energy than CaIn2O4, is not only a good photocatalyst but also can be an excellent up‐conversion (UC) host to exhibits UC luminescence. In this work, Yb3+ and/or Er3+ doped SrIn2O4 phosphors were synthesized, and their UC luminescence properties were studied and compared with those in the CaIn2O4 host. The structure of SrIn2O4: 0.01Er3+ and SrIn2O4: 0.1Yb3+/0.01Er3+ samples were refined by the Rietveld method and found to that SrIn2O4: 0.1Yb3+/0.01Er3+ showed increasing unit cell parameters and cell volume, indicating In3+ sites were substituted successfully by Yb3+ and/or Er3+ ions. From the UC luminescence spectra and diffuse reflection spectra, Er3+‐doped SrIn2O4 showed very weak luminescence due to ground state absorption of Er3+; Yb3+/Er3+ codoped SrIn2O4 presented strong green (550 nm) and red (663 nm) UC emissions which were assigned to energy transfer from Yb3+ transition 2F7/2→2F5/2 to the Er3+ transition 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2. Comparing with CaIn2O4, Yb3+/Er3+ codoped SrIn2O4 showed obvious advantages with higher UC luminescent intensity. The pumping powers study showed that UC emissions in Yb3+/Er3+ codoped SrIn2O4 were attributed to energy transfer of Yb3+→Er3+ with a two‐photon process. The possible UC luminescent mechanism of Yb3+/Er3+‐doped SrIn2O4 was discussed.

Structural characterizations and intense green upconversion emission in Yb3+, Pr3+ co-doped Y2O3 nano-phosphor

We report the structural and optical properties of Yb3+, Pr3+ co-doped Y2O3 nano-phosphor synthesized through solution combustion method. The structural studies reveal the nano-crystalline structure of the sample. The energy dispersive spectroscopy (EDS) measurements confirm the presence of Y, O, Pr and Yb elements in the sample. Fourier transform infrared studies show the vibrational features of the samples. The fluorescence spectra of the samples have been monitored on excitation with 976nm and the intense green upconversion emission observed at 552nm is due to 3P0→3H5 electronic transition. The concentration of Pr3+ ion in the sample is optimized and the fluorescence intensity is maximum at 0.08mol% of Pr3+. The power dependence studies reveal the involvement of two photons in the emission process. The possible mechanism of upconversion has been discussed on the basis of schematic energy level diagram. The sample annealed at higher temperature enhances the fluorescence intensity up to 8 times and this enhancement is discussed in terms of the removal of optical quenching centers. The nano-phosphor can be applicable in the field of display devices and green laser.

Efficient green up-conversion emission in Yb3+/Ho3+ co-doped CaIn2O4

Intense green up-conversion (UC) emissions from 5F4/5S2→5I8 transitions of Ho3+ in Yb3+/Ho3+ co-doped CaIn2O4 have been observed with excitation at 980nm. The optimal processing parameters were determined by investigating emission intensities as a function of annealing temperature, duration time and Ho3+/Yb3+ dopant concentrations. It has been confirmed that the green UC luminescence was generated via a two-photon process from the quadratic dependence of the emission intensity on the pump power. A UC mechanism was proposed and the lifetime of the green emission was measured to be ∼204μs. The infrared-to-visible UC efficiency of the optimized CaIn2O4: 0.005Ho3+, 0.1Yb3+ sample increases to ∼5.5% with the excitation power and saturates at 1.5W. The chromaticity coordinates (0.281, 0.708) of the samples are located in the green region and hardly changed due to the negligible red emission. The results indicate that CaIn2O4: Yb3+, Ho3+ could act as an effective UC green light emitter and CaIn2O4 is an ideal oxide host for UC luminescence.

White upconversion emission in Yb3+/Tm3+/Ho3+ doped SrMoO4 nanocrystals by high excited state energy transfer

The SrMoO4:Yb3+/Tm3+/Ho3+ nanocrystals have been successfully synthesized via a sol–gel process. Under 976nm laser diode excitation, the nanocrystals show the intense white upconversion (UC) emission, which is composed of the blue (1G4→3H6 of Tm3+), green (5F4/5S2→5I8 of Ho3+), and red (5F5→5I8 of Ho3+) UC emissions. The UC mechanisms based on spectral, kinetic, and pump power dependence analyses were discussed. It indicates that the white UC emission is attributed to the high excited state energy transfer from the sensitizer Yb3+−MoO42− dimer to the activators (Tm3+ and Ho3+), which can partly decrease the non-radiative processes at the lower energy levels of the activators.

Comparative Investigation of Green and Red Upconversion Luminescence in Er3+ Doped and Yb3+/Er3+ Codoped LaOCl

Pure tetragonal LaOCl:Er3+ and LaOCl:Yb3+/Er3+ samples possessing upconversion (UC) luminescence behavior were synthesized using a simple solid‐state reaction method and the structural properties were investigated using X‐ray diffraction, crystal structure analysis, and SEM, respectively. The UC spectroscopic properties of Er3+ doped and Yb3+/Er3+ codoped LaOCl were studied in terms of UC emission spectra. The intense green and red emissions around 528, 550, and 662 nm corresponding to the 2H11/2→4I15/2, 4S3/2→4I15/2, and 4F9/2→4I15/2 transitions of Er3+ ions were observed for LaOCl:Er3+ sample under excitation at 980 nm, and the power studies indicated that two‐photon processes were responsible for the green and red upconversion luminescence. The bright green emission is visible to the naked eyes for LaOCl:Er3+. A great enhancement of the visible upconversion emissions in Yb3+/Er3+‐codoped sample was observed, furthermore, it is interesting to find the bright red emission for LaOCl:Yb3+/Er3+ samples. The mechanisms for the green and red UC luminescence, especially the enhancement of red UC emission were discussed based on the law of UC intensity versus pump power and their lifetimes.

Red, green, blue and white light upconversion emission in Yb3+/Tm3+/Ho3+ co-doped tellurite glasses

Several Yb3+/Tm3+/Ho3+ co-doped transparent TeO2–ZnO–Na2O–Yb2O3–Ho2O3–Tm2O3 glasses were prepared and luminescence properties were characterized. Simultaneous red, green and blue (RGB) emission were obtained after excitation at 970 nm. Colour emission was tuned from multicolour to white light with colour coordinate (0.32, 0.33) matching very well with the white reference (0.33, 0.33). Changes in colour emission were obtained by varying the intensity ratios between RGB bands that are strongly concentration dependent because of the interaction of co-dopants. The colour tunability, high quality of white light and high intensity of the emitted signal make these transparent glasses excellent candidates for applications in solid-state lighting.

Upconversion emissions in Yb3+–Tm3+-doped tellurite glasses excited at 976 nm

Intense Tm3+ blue upconversion emission has been observed in Tm3+-Yb3+ codoped oxyfluoride tellurite glass under excitation with a diode laser at 976 nm. Three emission bands centered at 475, 650 and 796 nm corresponding to the transitions (1)G(4) -> H-3(6), (1)G(4) -> H-3(4) and F-3(4) -> H-3(6), respectively, simultaneously occur. The dependence of upconversion intensities on Tm3+ ions concentration and excitation power are investigated. For fixed Yb2O3 concentrations of 5.0 mol%, the maximum upconversion intensity was obtained with Tm2O3 concentration of about 0.1 mol%. The blue upconversion luminescence lifetimes of the Tm3+ transitions (1)G(4) -> H-3(6) are measured. The results are evaluated by the possible upconversion mechanisms.

Mechanism of the enhanced upconversion emissions in Yb3+/Er3+-codoped germanate-tellurite glasses

The intensity of upconversion emissions of rareearth ions is determined by the maximum phonon energy of glass host. In this paper the intensities of upconversion emissions in Yb3+/Er3+codoped germanatetellurite glas ses upon the excitation of 980nm laser diode were extremely enhanced by replacing PbO wit h Bi2O3 and increasing the size of alkalimetal ions. Rama n spectra show tha t the maximum phonon energies of the glass hosts investigated keep unchanged, wh ile the maximum phonon density decreases on substituting Bi2O3 for PbO and i ncreasing the size of alkalimetal ions. Based on the nonradiative decay rate, it is found that the maximum phonon density is the main reason for the enhanceme nt of upconversion emissions in Yb3+/Er3+codoped germana tetellurite glasses.

Blue Upconversion Emission in Yb3+ and Tm3+ CodopedLead–Germanate–Tellurite Glasses

Intense blue and red upconversion emissions have been observed inYb3+/Tm3+ co-doped0.05 K2O-0.1ZnO-0.1BaO-0.2PbO-0.2GeO2-0.35TeO2glasses under the pump of 976-nm laser diode. The dependence of theintensity of the upconversion emissions on the Tm3+concentration has been studied in order to determine the ionconcentration and the involved mechanism. The blue emission centred at476 nm decreases and the 792-nm red emission increases with theincreasing Tm3+ concentration. Subsequently, the dependence ofupconversion emission intensity on the excitation power isinvestigated. It is found that the intensity ratio between the 792-nmred and 476-nm blue emissions decreases with the increasing pumpenergy.

Upconversion dynamics in Yb3+–Ho3+ doped fluoroindate glasses

The mechanisms and dynamics of the upconversion emissions in Yb3+–Ho3+-doped fluoroindate glasses by exciting at 975 nm have been analysed. The upconversion efficiencies have been measured as a function of temperature in the range from 12 to 295 K. The temporal evolution of the 545- and 650-nm upconversion emissions obtained under flash excitation at 975 nm in codoped samples with 2.25 mol.% of Yb3+ and 0.75 mol.% of Ho3+ cannot be described using the energy migration model. This indicates that at this concentration of Yb3+ the rapid migration regimen between these ions has not been reached. A model is proposed in order to explain the temporal evolution of these emissions taking into account energy migration between donors and backtransfer processes.

Blue up-conversion emission in Yb3+ sensitized YAG:Pr3+

One-color infra-red laser pumping of YAG:Pr3+ + Yb3+ crystals results in a strong up-converted blue fluorescence from the excited3P0 multiplet. Up-conversion fluorescence intensity increases as the square of incident pump power indicating two-ion process. The first step is the efficient nonradiative energy transfer from2F5/2 level of Yb3+ to the1G4 level of Pr3+. The second step is an excited-state absorption (ESA) from the1G4 multiplet. The resonance between the first-step pumping process and the second-step ESA is strongly temperature dependent.