Xixian Luo

Design and achieving of multicolor upconversion emission based on rare-earth doped tellurite

Yb3+/Tm3+ co-doped and Yb3+/Ho3+/Tm3+ tri-doped tellurite glasses were synthesized by fusing the mixture of TeO2, PbF2, AlF3, BaF2, Yb2O3, Tm2O3 and Ho2O3 in a corundum crucible at 850 °C for 20 min. The synthesized glasses were characterized by upconversion emission spectra under the excitation of 980 nm laser, and the emission colors were investigated according to the CIE-1931 standards. The results indicated that Yb3+/Tm3+ co-doped tellurite glass exhibited blue upconversion emission with favorable color coordinates of (0.20, 0.07). Yb3+, Ho3+ and Tm3+ tri-doped tellurite glasses presented white upconversion luminescence under a single 980 nm laser excitation. Moreover, a very wide range of emission colors could be tuned by altering Ho3+ concentration. Combining the contribution of adjusting Ho3+ concentration and pump power, near equal energy white light was obtained.

Upconversion luminescence of Y2Ti2O7:Er3+ under 1550 and 980 nm excitation

Abstract Er 3+ doped Y 2 Ti 2 O 7 phosphors were prepared by the high temperature solid state reaction method at 1500 °C. X-ray diffraction and luminescence spectra were used to characterize the properties of samples. Due to the layer distribution of Y 3+ ions in the pyrochlore Y 2 Ti 2 O 7 crystal, Er 3+ ions, replacing Y 3+ in Y 2 Ti 2 O 7 crystal, could realize high-concentration doping by suppressing energy migration between layers to minimize concentration quenching. Investigation on the upconversion characteristic of Y 2 Ti 2 O 7 :Er 3+ showed that the optimal doping concentration of Er 3+ was up to 28 mol.%. Y 2 Ti 2 O 7 :0.28 Er 3+ exhibited both dominating red emission under 980 and 1550 nm excitation. The brightness of Y 2 Ti 2 O 7 :0.28Er 3+ were 4 times (980 nm) and 7 times (1550 nm) higher than that of Y 2 Ti 2 O 7 :0.05Er 3+ . And Y 2 Ti 2 O 7 :Er 3+ presented much better red emission color purity and stability under 1550 nm excitation.

Upconversion photoluminescence properties of SrY2O4:Er3+,Yb3+ under 1550 and 980 nm excitation

Abstract Er 3+ /Yb 3+ co-doped SrY 2 O 4 phosphors with high color purity and brightness were successfully synthesized via a solid-state reaction method. Luminescence spectrum studies showed that the main red peaks and the minor green peaks of upconversion emissions were located at approximately 634–681 nm and 543–570 nm, respectively, corresponding to the transitions of 4 F 9/2 ? 4 I 15/2 and 4 S 3/2 ? 4 I 15/2 of Er 3+ ions. Under the excitation of 980 and 1550 nm lasers, the spectra of all of the samples exhibited similar peak positions but different intensities. When excited by the 980 nm laser, the intensity ratio of red to green emission increased with increasing Yb 3+ doping concentration and decreased with increasing excitation power. In the case of 1550 nm excitation, the intensity ratio of red to green emission increased with increasing Yb 3+ doping concentration and excitation power, thereby, improving the color purity of the red emission. The intensity of red emission was considerably stronger under 1550 nm excitation than that under 980 nm excitation. Therefore, the color of the proposed phosphors could be efficiently tuned by tailoring both the Yb 3+ doping concentration and excitation power.

Preparation and stabilization of γ-La2S3 at low temperature

Abstract Eu doped γ-La 2 S 3 were synthesized by the sulfurization of their oxide powders using CS 2 gas at 700 °C. During the sulfurizing reaction process, the cubic Eu 3 S 4 crystals of prior formation acted as the nuclei sites of the γ-La 2 S 3 phase to facilitate the nucleation process. The γ-La 2 S 3 transformation occurred at significantly lower temperature by the combined contributions of low transformation enthalpy and induced multiple nuclei. On the other hand, the doped Eu ions could be inserted into the empty tetrahedral S 4 cavities to stabilize the γ-La 2 S 3 phase at temperature excess of 1100 °C.

Preparation and upconversion luminescence of monodisperse Y2O2S:Yb/Ho-silica/aminosilane core-shell nanoparticles

Abstract Y 2 O 2 S:Yb/Ho-silica/aminosilane core-shell nanoparticles were prepared by a solid-gas method in combination with polyvinylpyrrolidone assisted one-step ammoniating method. The core was a single Y 2 O 2 S:Yb/Ho with 80 nm in diameter and the shell was silica/aminosilane with around 5 nm in thickness. The results of sedimentation experiment indicated that the nanoparticles could be well-dispersed in ethanol and water to form stable colloids. Since the coating weakened lattice vibration energies of the Y 2 O 2 S:Yb/Ho particles, the proportion of upconversion processes in the depletion of Ho 3+ 5 I 6 level were increased, resulting in increase of green light and decrease of red light.

Preparation of γ-Gd2S3 via thermolysis of Gd[S2CN(C4H8)]3·phen coordination

Abstract Pure γ-Gd 2 S 3 was synthesized by the thermolysis of a single Gd[S 2 CN(C 4 H 8 )] 3 phen complex precursor in a flow of argon carrier gas containing sulfur vapor. The complex precursor was decomposed into amorphous Gd 2 S 3 and carbon at about 350 C. Crystalline γ-Gd 2 S 3 could be achieved at temperature exceeding 600 C, and the obtained γ-Gd 2 S 3 presented a very high degree of crystallinity at 800 C. Carbon prevented the formation of Gd 2 O 2 S impurity in the preparation of γ-Gd 2 S 3 . However, the carbon blackened the product. At temperature ≥1000 C, the residual carbon impurity could be efficiently removed by introducing sulfur into the system for the volatile CS 2 could be formed in situ via the reaction of sulfur with the deposited carbon. In the meantime, S also promoted the crystallization of γ-Gd 2 S 3 remarkablely.

Simple method for simultaneously achieving red and green up-conversion luminescence

The simultaneous emission of red and green light with high brightness and color purity was obtained from Er3+-doped NaYbF4-based up-conversion nanoparticles excited by 980 and 1550 nm excitation. The 2F5/2 level of Yb3+ showed high absorption efficiency at 980 nm. The 4I13/2 level of Er3+, an excellent UC intermediate with high energy and a long lifetime (milliseconds), absorbed more energy in the cross section (6.0 × 10−20 cm2) than did the Yb3+ 2F5/2 level (1.2 × 10−20 cm2) and was efficiently and directly pumped by light with a wavelength of ∼1500 nm. In contrast to particles resulting from other methods using complex coating for achieving multi-color emission in a single sample, the as-prepared luminescent NaYbF4:25% Er3+ up-conversion nanoparticles were designed to be single-layered and spherical and showed excellent dispersibility and uniform sizes. Nanoparticles prepared by this method exhibit a great advantage based on the simple preparation process and small particle size. On this basis, we expect to easily achieve the emission of three primary colors by these reasonably designed core–shell particles.

K3LaTe2O9:Er: a novel green up-conversion luminescence material

A novel green up-conversion luminescence material, K3LaTe2O9:Er, was synthesised via a solid-state reaction method. K3LaTe2O9:Er phosphors were characterised by X-ray diffraction, reflectance spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, up-conversion spectroscopy and temperature sensing performance analysis. The diffraction pattern of the hexagonal K3LaTe2O9:0.02Er microcrystals was indexed with Miller indices and the lattice constants were a = b = 0.60636 ± 0.00018 nm, and c = 1.49543 ± 0.00037 nm. The photoluminescence under 380 nm excitation and the up-conversion luminescence under 980 and 1550 nm pumping were investigated. The influence of Er3+ ion concentration and excitation power on the luminescence properties of K3LaTe2O9:Er was also discussed. K3LaTe2O9:Er phosphor presented green down-shifting emission and up-conversion luminescence under 380, and 980 nm excitation and yellow–green up-conversion luminescence under 1550 nm pumping, respectively, and the red emission component was enhanced with the increment in excitation wavelength. The quenching concentration of Er3+ ions in K3LaTe2O9:Er was much higher than that in normal phosphors. This result can be attributed to the suppression of energy migration because the shortest (0.606 nm) and average distance (0.9720 nm) between Er3+ ions were significantly large in K3LaTe2O9. Therefore, the electric quadrupole–quadrupole interactions between Er3+ ions are the dominant energy transfer process in down-shift emission, and the UCL mechanism can be regarded as the excited state absorption in K3LaTe2O9:Er. Furthermore, the doping concentration of Er3+ ions influenced the temperature sensitivity of K3LaTe2O9:Er.

Up-conversion luminescence of Er2Mo4O15 under 980 and 1550 nm excitation

Y2−xErxMo4O15 (x = 0.04, 0.08, 0.16, 0.32, 0.64, 2.0) phosphors were synthesised at 700 °C through a solid-state reaction method. The samples were characterised by XRD and emission spectra analysis. Y2−xErxMo4O15 samples showed a strong green emission (2H11/2, 4S3/2 → 4I15/2) and a weak red emission (4F9/2 → 4I15/2) under 1550 and 980 nm excitation. The green emission intensity was enhanced increasing the Er3+ ion doping content, whereas the red emission was basically unchanged. Thus, Er2Mo4O15 exhibited an abnormal green up-conversion luminescence without concentration quenching under 1550 and 980 nm excitation. The dominating green up-conversion luminescence was due to the larger adjacent Er3+⋯Er3+ distance caused by the special structure of Er2Mo4O15, which limited the energy-transfer process and cross-relaxation responsible for the red up-conversion emission. Therefore, the up-conversion luminescence mechanism was excited-state absorption under 1550 nm excitation.

Upconversion luminescence properties of Y 2 O 3 :Yb, Er and Y 2 O 2 S:Yb, Er nanoparticles prepared by complex precipitation

The Yb3+, Er3+ doped Y2O3 and Y2O2S upconversion nanophosphors were prepared by the direct complex precipitation method with the mixed solution of NH4HCO3 and NH3ċH2O as the complex precipitant. The precipitate of Re(OH)x(CO3)y calcined at 900°C in air presents the pure Y2O3 with cubic structure, and the calculated crystalline size is about 26 nm, while the Y2O2S:Yb, Er nanocrystals were obtained by annealing the same precipitate at 900°C but in the atmosphere of N2 gas containing sulfur vapor. The obtained sample presents the pure hexagonal structure of Y2O2S with calculated crystalline size of 29 nm. According to the transmission electronic microscopy (TEM), the nanophosphors exhibit uniform quasispherical shape and size about 30 nm. By using the 980 nmexcitation laser, the properties of upconversion luminescence and energy transfer processes were studied in detail for the different concentration of Yb3+ in Er3+ doped Y2O3 as well as the Yb3+, Er3+ codoped Y2O2S nanocrystals. The high-efficient red and yellow upconversion emissions were both observed by naked eyes in day time corresponding to the Y2O3:Yb, Er and Y2O2S:Yb, Er phosphors, respectively. Thus the upconversion nanoparticles combining its high efficient emission would pave the way for ideal fluorescence probes in biological applications.