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Abstract: Pr3+, Yb3+ co-doped CaYAlO4 (Pr, Yb: CYA) single crystal was grown using the Czochralski (CZ) method. For near-infrared quantum-cutting system, a quantum efficiency of 145% for Pr3+, Yb3+-codoped CYA crystal has been obtained by ignoring the nonradiative losses. Under excitation at 940nm, high intensities of 502nm, 555nm, 628nm, 661nm and 729nm emissions turn up. Fluorescence decay time of 3P0→3F2 emission of Pr3+ ions and 2F5/2→2F7/2 transition of Yb3+ ions were also studied as evidences for energy transfer. [Copyright &y& Elsevier]

Abstract: Infrared (1.2–1.6μm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (λ =940nm). The Cr4+ emission band was observed with its peak at 1.34μm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (λ =1.03μm). We demonstrate that for the excitation wavelength of 940nm Yb3+ ions act as sensitizers of the 3B2(3T2)–3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2–1.6μm) output. [Copyright &y& Elsevier]

Abstract: In this paper, we present results on upconversion luminescence performed on Yb3+-doped yttrium aluminum garnets under 940nm excitation. The upconversion luminescence was ascribed to Yb3+ cooperative luminescence and the presence of rare earth impurity ions. The cooperative luminescence spectra as a function of Yb concentration were measured and the emission intensity variation with Yb concentration was discussed. Yb3+ energy migration quenched the cooperative luminescence of Yb:YAG crystals with doping level over 15at%. [Copyright &y& Elsevier]

Abstract: Infrared (1.2–1.6μm) luminescence in a yttrium aluminium garnet (YAG) crystal, co-doped with Yb (10 at.%) and Cr (0.05 at.%) ions, was investigated under CW laser diode pumping (λ =940nm). The Cr4+ emission band was observed with its peak at 1.35μm and measured to be about 6% with respect to Yb3+ IR luminescence (λ =1.03μm). Analysis of the crystal absorption and luminescence spectra allows one to conclude that Yb3+–Cr4+ energy transfer is a mechanism responsible for the 3B2(3T2)–3B1(3A2) emission of Cr4+ ions. This crystal is promising as an efficient source of the near infrared emission. [Copyright &y& Elsevier]

2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0, 0.1, 0.5 and 1) transparent ceramics were fabricated via vacuum sintering. The microstructural properties of the prepared ceramics were determined using XRD and SEM. The absorption cross-section of 2 at.% Tm, 1 at.% Dy:Y 2 O 3 ceramic was 0.53 × 10−20 cm2 with the FWHM of 43.59 nm. The increased cross-section originates from a large overlapping range appearing in the absorption spectrum of the Dy3+:6H 15/2 → 6F 5/2 and Tm3+:3H 6 →6H 4 transitions. The J-O intensity parameters Ω 2 , Ω 4 and Ω 6 and the fluorescence characteristics of the pivotal luminescent level of the Dy3+ ions were investigated. Under 793 nm excitation, the emission cross section of the Tm,Dy:Y 2 O 3 ceramic at 3094 nm was 3.63 × 10−21 cm2 with the FWHM of 355 nm. The fluorescence lifetimes of Dy3+:6H 13/2 level of 2 at.% Tm, xat.% Dy:Y 2 O 3 (x = 0.1, 0.5 and 1) ceramics were fitted to be 357 μs, 282 μs and 149 μs, respectively. In order to explore the quenching mechanism of Tm3+:3F 4 level, the fluorescence lifetimes of Tm3+:3F 4 of the 2 at.% Tm, xat.% Dy:Y 2 O 3 ceramics (x = 0, 0.1, 0.5 and 1) were measured to be 4.878 ms, 462 μs, 104 μs and 61 μs, respectively. The possible energy transfer mechanisms between Tm3+ and Dy3+ ions are discussed. The results show that adding Tm3+ ions to Dy:Y 2 O 3 ceramics can effectively enhance the 2.9 μm MIR through energy transfer. [ABSTRACT FROM AUTHOR]

High quality Dy3+: BaF 2 and Dy3+/RE3+ (RE = Tb, Eu): BaF 2 crystals were successfully grown by temperature gradient technology (TGT). The visible spectroscopic properties as well as the energy transfer mechanism of Dy3+ and Tb3+/Eu3+ co-doped BaF 2 crystals were systematically discussed. The spectral performance at 575 nm (Dy3+: 4F 9/2 → 6H 13/2) emission was significantly improved by co-doping Tb3+/Eu3+ ions. Through the upper level lifetime changed, it can be proved that there is a quasi resonance energy transfer between Dy3+: 6H 13/2 and Tb3+: 7F 4 / Eu3+: 7F 4 states, and the final gain effect exceeds negative influence of the upper level energy transfer. Meanwhile, the optimal concentration ratio of Dy3+/Tb3+ and Dy3+/Eu3+ in double-doped crystals was relatively different. The optimal ratio of Dy3+/Tb3+ was 10:1 in 2%Dy3+,0.2%Tb3+: BaF 2 crystal. The emission cross section increases from 8.147 × 10−22 cm2 to 11.284 × 10−22 cm2 with an increase of 38.5 %, and the quality factor (σ em ⋅τ) increases by 22.3 %. The optimal ratio of Dy3+/Eu3+ was 20:1 in 2%Dy3+,0.1%Eu3+: BaF 2 crystal, the emission cross section is increased to 10.411 × 10−22 cm2 with an increase of 27.8 %, and the quality factor increases by 26.9 %. The above results show that Dy3+: BaF 2 crystals co-doped with deactivated ions (Tb3+/Eu3+) of low concentration have great potential as gain media for yellow laser output. • High quality Dy3+:BaF 2 and Dy3+/Re3+(Re Tb, Eu):BaF 2 crystals were grown by TGT, and various performance was measured. • Various spectral performance of Dy3+:BaF 2 has been improved by Tb3+/Eu3+ doped, and the maximum increase is up to 38.5 %. • These results show that Dy3+/Re3+(Re Tb, Eu):BaF 2 crystals have great potential as yellow laser medium. [ABSTRACT FROM AUTHOR]

• Ba 2 LaNbO 6 :Cr3+,Yb3+ double perovskite far-red and near-infrared phosphors were synthesized by high-temperature solid-state method. • Under 324 nm UV excitation, Ba 2 LaNbO 6 :Cr3+,Yb3+ phosphors emit far-red and near-infrared light in the ranges of 620–760 nm and 920–1120 nm, corresponding to the transitions Cr3+:2E→4A 2 and Yb3+:2F 5/2 →2F 7/2 , which coincides well with the absorption spectra of photosensitive pigment P FR and photosynthetic bacteria, respectively. Ba 2 LaNbO 6 :Cr3+,Yb3+ double perovskite far-red and near-infrared phosphors were synthesized by high-temperature solid-state method. The crystal structure and optical properties were systematically investigated, encompassing PL, PLE, and temperature-dependent PL spectra. The calculated value D q /B of Ba 2 LaNbO 6 :0.005Cr3+ phosphor was calculated to be 2.59, signifying a robust crystal field strength within the [NbO 6 ] octahedral environment occupied by Cr3+ ions. Under 324 nm UV excitation, Ba 2 LaNbO 6 :Cr3+,Yb3+ phosphors emit far-red and near-infrared light in the ranges of 620–760 nm and 920–1120 nm, corresponding to the transitions Cr3+:2E→4A 2 and Yb3+:2F 5/2 →2F 7/2 , which coincides well with the absorption spectra of photosensitive pigment P FR and photosynthetic bacteria, respectively. The energy transfer mechanisms involving Cr3+ and Yb3+ ions were also thoroughly investigated. The results demonstrate that Ba 2 LaNbO 6 :Cr3+,Yb3+ phosphors have potential applications in plant cultivation LEDs. [ABSTRACT FROM AUTHOR]

Yb,Tb:YAG crystals with various Yb3+ and Tb3+ concentration were grown by the micro-pulling-down method (μ -PD). The absorption spectra, fluorescence spectra and fluorescence decay curves of Yb,Tb:YAG crystals were measured at room temperature. Under 980 nm excitation, Yb,Tb:YAG crystals exhibited intense visible up-conversion luminescence due to the cooperative energy transfer from two Yb3+ ions to one Tb3+ ion. Under 485 nm excitation, Yb,Tb:YAG crystals yielded near-infrared down-conversion emission, ascribing to the cooperative absorption of pumping photons and cooperative energy transfer from one Tb3+ ion to two Yb3+ ions. The energy transfer processes from Yb3+ ions to Tb3+ ions were discussed, and the energy transfer efficiency was calculated. Based on studies of the obtained results, Yb3+/Tb3+ co-doped YAG crystal shows promising potential for sensing, volumetric displays, optical data storage, light emitting diodes. • Yb,Tb:YAG single crystals grown by the micro-pulling-down technique. • The cooperative energy transfer process was analyzed. • The effect of doped concentration on energy transfer efficiency was discussed. [ABSTRACT FROM AUTHOR]

• After co-doping Tb3+ ions, the Ω4/Ω6 increased 1.57 from to 1.66. • The branching ratios of the 3H 4 →3F 4 transition also strengthened. • The decay curve of 3F 4 level doped with different Tb3+ ions concentration decreased. • Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. Tm3+ and Tb3+ co-doped Y 3 Al 5 O 12 (YAG) ceramics were fabricated by high temperature solid state reaction under oxygen sintering. The absorption spectra, fluorescence spectra and fluorescence decay curves of Tm,Tb:YAG ceramics were measured. The spectral parameters of Tm,Tb:YAG ceramic were calculated. The lifetimes of Tm3+:3F 4 level of Tm,Tb:YAG ceramics were calculated to be 11.28, 2.12, 1.24, 0.63 and 0.49 ms for the Tb3+ doping concentration of 0, 0.1, 0.2, 0.35 at 0.5 at%, respectively. The co-doping Tb3+ ion is a productive deactivator that could reduce the filling of 3F 4 mainfold and enhance the emission of 3H 4 →3F 4 transition. These results indicate that the addition of Tb3+ ions in Tm,Tb:YAG ceramic could be a promising technique for laser operation around 1.5 µm. [ABSTRACT FROM AUTHOR]

Abstract: The Mn-, Cr-doped and Mn, Cr-co-doped MgAl2O4 powders have been synthesized via a gel–solid reaction method. Energy transfer from Mn2+ to Cr3+ has been observed for the first time in the co-doped MgAl2O4 phosphors. When excited with blue light with a wavelength of 450nm at room temperature, both green emission from Mn2+ around 520nm and red emission from Cr3+ around 675and 693nm were generated. Moreover, the color of the emission can be modified by controlling the doping concentrations of Mn2+ and Cr3+. Therefore, MgAl2O4: Mn2+, Cr3+ could be used as a single-phased phosphor for white LED with a blue LED chip. The energy transfer in terms of Mn2+ to Cr3+ is determined by means of radiation and reabsorption. [Copyright &y& Elsevier]

Photograph of Yb,Ho:YAG crystals grown by the μ-PD method. (a) Yb = 0.05, (b) 0.1, (c) 0.15. • Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. Y 3 Al 5 O 12 (YAG) single crystals doped with a fixed Ho3+ content of 0.5 at.% and various Yb3+ contents (Yb = 5, 10 and 15 at.%) have been successfully grown by the micro-pulling-down (μ-PD) method. The absorption spectra, fluorescence spectra and fluorescence decay curves were recorded at room temperature. The intense emission of Yb,Ho:YAG crystal centered at 2 μm corresponds to the 5I 7 → 5I 8 transition. Three intense emissions centered at 524–569 nm, 623–691 nm and 744–746 nm, correspond to the 5F 4 + 5S 2 → 5I 8 , 5F 5 → 5I 8 and 5F 4 + 5S 2 → 5I 7 transitions, respectively. The possible energy transfer mechanisms were discussed intensively. [ABSTRACT FROM AUTHOR]