Cooperative Energy Transfer Up-/Down-Conversion Luminescence in Tb³⁺/Yb³⁺ Co-Doped Cubic Na₅Lu₉F₃₂ Single Crystals by Gd³⁺ Co-Doping

Abstract

The luminescence properties of Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ , Yb 3+ , and Gd 3+ ions synthesized via a vertical Bridgman method were reported. Gd 3+ was codoped as a sensitizer in Na 5 Lu 9 F 32 :Tb 3+ , Yb 3+ , thus increasing the absorption line-width and the absorption cross sections in the ultraviolet− visible region. Effects of Gd 3+ concentration on the luminescence properties under ultraviolet and near-infrared were investigated. The energy transfer mechanism between the Gd 3+ and Tb 3+ ion was witnessed by the detailed analyses of the excited-state lifetimes, emission quantum yields, and emission and excitation spectra for the Na 5 Lu 9 F 32 :Tb 3+ , Yb 3+ single crystals codoping with various Gd 3+ concentrations ranging from 0 to 0.25 mol %. Following the excitation light in ultraviolet region, Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ /Yb 3+ /Gd 3+ showed dominant green emissions in the visible region and at 980 nm which were attributed to 5 D 4 → 7 F 5 transition of Tb 3+ and 2 D 5/2 → 2 F 7/2 of Yb 3+ , respectively. Under the excitation of 980 nm, Na 5 Lu 9 F 32 single crystals tridoped Tb 3+ /Yb 3+ /Gd 3+ presented bright yellowish-green lights arising from the cooperative energy transfer between two Yb 3+ and one Tb 3+ . The practical up-conversion and down-conversion external quantum efficiency were measured by integrating spheres at ∼1.2% and ∼45%, respectively. The present results demonstrated successful Tb 3+ /Yb 3+ /Gd 3+ triply doping Na 5 Lu 9 F 32 single crystals with both up-and down-conversion luminescence properties that can be used as a potential spectrum converter in solar cells.

Effects of Yb2O3 as Stabilizer and Sensitizer on the Luminescence Properties of Cubic ZrO2 Single Crystals

“…All samples have peaks at 257, 915, 965, and 1030 nm. Those at 915, 965, and 1030 nm result from splitting of the 2 F 5/2 energy state in the 2 F 7/2 to 2 F 5/2 transition in the Yb 3+ ion, − and the intensity in the 900–1000 nm range is proportional to the Yb 3+ content of the crystals. In contrast, the absorption at 257 nm represents the charge transfer transition from O 2p to Zr 4d.…”

Enhanced upconversion and downshifting emissions from Tb3+, Yb3+ co-doped CaZrO3 phosphor in presence of Li+ ions

“…Figure 3 shows the UC emission spectrum of Tb 3+ ,Yb 3+ :CaZrO 3 phosphor sample on excitation with 980 nm radiation at 0. [29,30]. In this, the green emission peak centered at 545 nm has maximum intensity.…”

“…Since, the energy of 5 D 4 level of Tb 3+ ion is almost double to the energy of 2 F 5/2 level of Yb 3+ ion hence, the stepwise energy transfer from Yb 3+ to Tb 3+ ions is not possible. Only the cooperative energy transfer (CET) from Yb 3+ to Tb 3+ ions is possible [30]. In CET, two excited Yb 3+ ions cooperatively transfer their excitation energy simultaneously to Tb 3+ ions to promote them in 5 D 4 level.…”

Probing multimodal light emission from Tb3+/Yb3+-doped garnet nanophosphors for lighting applications

“…The slope values were found to be slightly lower than the expected value of 2.0, according to the energy level structure of these emissions for the two-photon absorption process. 60,61 These low slope values could be due to the involvement of non-radiative transitions and energy transfer processes that populate these emitting levels.…”