Spectroscopic properties and mechanism of Tm^(3+)/Er^(3+)/Yb^(3+) co-doped oxyfluorogermanate glass ceramics containing BaF_2 nanocrystals

Transparent Tm^3＋/Er^3＋/yb^3＋ co-doped oxyfluorogermanate glass ceramics containing BaF2 nanocrystals are prepared. Under excitation of a 980-nm laser diode （LD）, compared with the glass before heat treatment, the Tm^3＋/Er^3＋/yb^3＋ co-doped oxyfluorogermanate glass ceramics can emit intense blue, green and red up-conversion luminescence and Stark- split peaks; X-ray diffraction （XRD） and transmission electron microscope （TEM） results show that BaF2 nanocrystals with an average diameter of 20 nm are precipitated from the glass matrix. Stark splitting of the up-conversion luminescence peaks in the glass ceramics indicates that Tm^3＋, Er^3＋ and （or） Yb^3＋ ions are incorporated into the BaF2 nanocrystals. The up-conversion luminescence intensities of Tm^3＋, Er^3＋ and the splitting degree of luminescence peaks in the glass ceramics increase significantly with the increase of heat treat temperature and heat treat time extension. In addition, the possible energy transfer process between rare earth ions and the up-conversion luminescence mechanism are also proposed.

Enhancement in Laser Performance of Er^(3+)/Yb^(3+) Co-doped Phosphate Glass Materials

Er3＋/Yb3＋co-doped phosphate are presented, laser glass materials with composition of P2O5-A12O3-Ba CO3-KNO3-Li2O-Zn O-Er2O3-Yb2O3（R-PABKLZ） are presented, in which an optimal molar ratio of 1：4 between Er3＋ and Yb3＋ was observed for achieving peak laser gain. Furthermore, due to adding 4.7 mol% Li1＋ and 4.6 mol% Zn2＋ ions into the glass, an optimum composition structure based laser material was demonstrated. On the other hand, since the high temperature melting method with changeable temperature control was used, the emission cross section of fl uorescence, excited lifetime, and an effective spectral half width reached 9.70 × 10-21 cm2, 8.20 ms, and 53.16 nm, respectively, so that a laser gain（semi× rad） of 103.05 was obtained, which is signifi cantly higher than previously reported results. The manuscript also argued the mechanism of relevant laser gain improvement.

Structural and optical studies of Yb^(3+),Er^(3+) and Er^(3+)/Yb^(3+) co-doped phosphate glasses

Phosphate glass samples with various Yb2O3 and Er2O3 contents were synthesized by the conventional melt quenching technique and characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy. The absorption, emission spectra and fluorescence decay studies were carried out both at low and room temperatures. Results showed the existence of several sites occupied by the rare earth ions in the phosphate glass. Up-conversion and cooperative fluorescence were also discussed.

Emissions of Er3+ and Yb3+ co-doped SrZrO3 nanocrystals under near-infrared and near-ultraviolet excitations

In this study,the upconversion(UC)emissions of Er3+and Yb3+co-doped SrZrO3 nanocrystals(NCs)were investigated in terms of the thermal annealing temperature and concentration of Er3+ions and compared with the emissions under a near-ultraviolet(near-UV)excitation.The NCs were synthesized by the combustion method,and the as-synthesized NCs were post-annealed at high temperatures.The X-ray diffraction patterns revealed that the grain sizes and crystallinity degrees of the samples increased with increasing annealing temperatures.The photoluminescence spectra of our samples exhibited strong green and very weak red emissions with the near-UV excitation,originating from the f-f transitions in the Er3+ions.Interestingly,under near-infrared(near-IR)excitation,we identified sizable visible emissions at 525,547,and 660 nm in our NCs,which indicated that the UC process successfully occurred in our NCs.These UC emissions were maximized in the NCs with an Er3+concentration of 0.02 and thermal annealing at 1000°C.We found that the intensity ratios of red to green emissions increased with increasing annealing temperatures.We discussed the differences in the emissions between near-UV and near-IR excitations.

Preparation and characterization of Er^(3+)-Yb^(3+)-Ce^(3+) co-doped transparent glass ceramic containing nano Ca_5(PO4)_3F crystals

A transparent glass ceramic tri-doped with Ce3＋/Er3＋/yb3＋ was fabricated by the high-temperature melting technique and following heat-treatment. X-ray diffraction and transmission electron microscope results demonstrated that Cas（PO4）3F（FAP） nanocrystals, possessed with preferable emission performances for the 1.54 μm transition for doping Er3＋, were homogeneously pre- cipitated among the glass matrix with a mean size of 30 rim. Addition of Ce3＋ greatly enhanced 1.54 ~tm fluorescence of Er3＋ by the cross relaxation energy transfer between Er3＋ and Ce3＋. Meanwhile, incorporation of Ce3＋ dramatically decreased the visible upcon- version emission intensity of glass ceramic than that of glass, suggesting that Ce3＋ might incorporate into the FAP nanocrystals. The properties of this transparent glass ceramic showed the potential application as an efficient 980 nm pumped infrared laser medium.

Investigation of Silver Nanostructures and Their Influence on the Fluorescence Spectrum of Erbium-Doped Glasses

Sodium borate glasses embedded with silver were made by the melt quenching technique. Glass transition temperature was recorded by thermal analysis of the sample. As made glasses revealed emission in the visible region under nitrogen laser and excimer laser excitations. Heat treatment was used to induce silver metallic particles. Absorption spectra revealed a peak at 417 nm due to surface Plasmon resonance. Particle size was estimated to be 2.6 ± 0.2 nm. Erbium and silver co-doped multielement oxide glasses were made by the melt quenching technique followed by heat treatment to induce nanoparticles. In heat treated samples, Er3+ luminescence increased 4× due to enhanced field in the vicinity of silver particles. Under excimer laser excitation, Er3+ and 2% Ag co-doped glass revealed Er3+ transitions due to enhanced field at the rare-earth ions. Under 795 nm laser excitation Er3+ green upconversion signals are found to be 4× stronger in 2% Ag co-doped, heat treated sample, than the others.

Silver nanoparticles enhanced near-infrared luminescence of Er^3＋/Yb^3＋ co-doped multicomponent phosphate glasses

A new way to improve the 1.53μm emission in Er3＋/Yb3＋ co-doped multicomponent phosphate glass was demonstrated by introducing silver nanoparticles （NPs） in rare-earth doped glass. The existence of Ag NPs was confirmed by absorption spectra and transmission electron microscopy （TEM） measurements. The homogeneous distribution of silver NPs could be observed by the TEM images. UV-Vis-NIR absorption spectra revealed that the surface plasmon band was centered at about 420 nm. The photoluminescence spectra of glass samples were used to investigate the effect of silver NPs on the fluorescence properties of Er3＋. Efficient 1.53μm emis-sion was obtained in prepared samples when pumped at 980 nm laser diode （LD）. The 1.53μm emission intensity could be enhanced 87% by doping 2 mol.% AgCl due to the increased localized field effect in the vicinity of NPs and the possible energy transfer from silver NPs to Er3＋ions. Our present work may point out one way to enhance the gain coefficient of Er3＋/Yb3＋ co-doped glass fiber.

An investigation on the magneto-optic properties of terbium gallium garnet under high magnetic field

This paper reports that a series of Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses have been prepared and their absorption spectra measured. The J-O intensity parameters Ωk （k = 2, 4, 6）, spontaneous radiative lifetime Trad, spontaneous transition probability A, fluorescence branching ratio β and oscillator strength fed of the Nd3＋ ions at room temperature are calculated based on Judd-Ofelt （J-O） theory. The temperature dependence of the up-conversion photoluminescence characteristics in a Nd3＋：Er3＋：Yb3＋ co-doped sample is studied under a 978 nm semiconductor laser excitation, and the energy transfer mechanisms among Yb3＋, Er3＋ and Nd3＋ ions are analysed. The results show that the J-O intensity parameters Ω2 increase when the Nd3＋ concentration of the Nd3＋：Er3＋：yb3＋ co-doped borosilicate glasses increases. The possibility of spontaneous transition is small and lifetimes are long at levels of 4F5/2 and 4F3/2. The intensity of Nd3＋ emissions at 595, 691, 753, 813 and 887 nm axe markedly enhanced when the sample temperature exceeds 400 K. The reasons being the cooperation of the secondary sensitization from Era＋ to Nd3＋ and the contribution of a multi-phonon.

Effect of concentration quenching on the spectroscopic properties of Er^(3+)/Yb^(3+) co-doped AlF_3-based glasses

A series of highly Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have been investigated in order to develop a microchip laser at 1.54 μm under 980 nm excitation. Measurements of absorption, emission and upconversion spectra have been performed to examine the effect of Er^(3+)/Yb^(3+) concentration quenching on spectroscopic properties. In the glasses with Er^(3+) concentrations below 10 mol%, concentration quenching is very low and the Er^(3+)/Yb^(3+) co-doped fluoroaluminate glasses have stronger fluorescence of 1.54μm due to the ~4I_(13/2)→~4I_(15/2) transition than that of Er^(3+) singly-doped glasses. As Er^(3+) concentrations above 10 mol% in the Er^(3+)/Yb^(3+) co-doped samples, concentration quenching of 1.54μm does obviously occur as a result of the back energy transfer from Er^(3+) to Yb^(3+). To obtain the highest emission efficiency at 1.54μm, the optimum doping-concentration ratio of Er^(3+)/Yb^(3+) was found to be approximately 1:1 in mol fraction when the Er^(3+) concentration is less than 10 mol%.