Stokes and anti-Stokes luminescence in Tm³⁺/Yb³⁺-doped Lu₃Ga₅O₁₂ nano-garnets: a study of multipolar interactions and energy transfer dynamics

Abstract

Nanocrystalline Lu3Ga5O12 garnets doped with Tm(3+)/Yb(3+) ions have been synthesized by a low cost and environmentally benign sol-gel technique and characterized for their structural, Stokes and anti-Stokes luminescence properties. The diffuse reflectance spectra of doped Lu3Ga5O12 nano-garnets have been measured to derive the partial energy level structure of Tm(3+) and Yb(3+) ions and possible energy transfer channels between them. Upon laser excitation at 473 nm, weak red and intense near-infrared Stokes emissions have been observed in the nano-garnets. The decay curves of (3)H4 and (1)G4 levels of Tm(3+) ions and the (2)F5/2 level of Yb(3+) ions have been measured upon resonant laser excitation and are found to be non-exponential in nature due to multipolar interactions. In order to know the kind of multipolar interaction among optically active ions, the decay curves are analyzed through the generalized Yokota-Tanimoto model. Moreover, under 970 nm laser excitation, intense blue anti-Stokes emission is observed by the naked eye in Tm(3+)-Yb(3+) co-doped Lu3Ga5O12 nano-garnets. The results show that as-synthesized nano-garnets may be useful in the field of phosphors and photonics.

Energy Back Transfer Induced Color Controllable Upconversion Emissions in La2MoO6:Er3+/Yb3+ Nanocrystals for Versatile Applications

“…The temperature-dependent FIR value, which is estimated from the green UC emission spectra of La 2 MoO 6 :Er 3+ /0.20Yb 3+ nanocrystals, is shown in Figure 6c. Clearly, a gradual enhancement in the FIR value is observed and it reaches its maximum value of around 3.16 at 663 K. Furthermore, the evaluated FIR value can be exponentially fitted to Equation (16). As disclosed (see Figure 6c), the value of coefficient A is fitted to be ≈15.8 and the value of ∆E/k is demonstrated to be about 1036 which approaches to the linear fitting result as displayed in Figure 6b.…”

“…Currently, many routes and strategies, such as tailoring the particle size, selecting various dopants, preparing the core–shell structure, and controlling the relaxation process, have been performed to modulate the emitting color of RE ions doped upconverting nanocrystals . As is known, the main nonradiative (NR) energy transfer (ET) mechanism of the UC emissions can be attributed to either multipolar interaction or exchange interaction which is largely dependent on the average critical distance between the dopants . Hence, the selection of various activator/sensitizer combinations or their concentrations is a facile and effective method to modulate the emitting color of the upconverting nanocrystals.…”

“…[11][12][13][14][15] As is known, the main nonradiative (NR) energy transfer (ET) mechanism of the UC emissions can be attributed to either multipolar interaction or exchange interaction which is largely dependent on the average critical distance between the dopants. [16,17] Hence, the selection of various activator/sensitizer combinations or their concentrations is a facile and effective method to modulate the emitting color of the upconverting nanocrystals. In comparison with other trivalent RE ions, the Er 3+ /Yb 3+ combinations, where the Yb 3+ ion is employed as the sensitizer on account of its large absorption cross section in the near-infrared (NIR) region and the Er 3+ ion acts as the luminescent center due to the featured green and red UC emissions originating from the intra-4f transitions, are regarded as promising candidates for upconverting materials.…”

Enhanced anti-stocks luminescence in LaNbO4:Ln3+ (Ln3+ = Yb3+, Er3+/Ho3+/Tm3+) with abundant color

“…38 For LNO:Yb 3+ /Tm 3+ , Tm 3+ ions are excited from ground state 3 H 6 level to 1 G 4 level by three energy transfer processes and the mechanism is expressed as follows: rstly, 3 H 6 (Tm) + 2 F 5/2 (Yb) / 3 H 5 (Tm) + 2 F 7/2 (Yb), and then the energy level 3 H 5 relaxes to 3 F 4 . Secondly, 3 [39][40][41] The concentration of sensitizer and activator is a signicant factor of the UCL properties. The concentration affects the relative amount of Ln 3+ in the samples and the average distance between adjacent dopant ions, leading to a signicant impact on the optical properties of the samples.…”

Phase evolution, structure, and up‐/down‐conversion luminescence of Li6CaLa2Nb2O12:Yb3+/RE3+ phosphors (RE = Ho, Er, Tm)

“…The garnet structure was also suggested to be desirable for UC luminescence, since in which the Yb 3+ sensitizer may present large ground‐state Stark splitting to form a quasi‐three energy level, which was expected to be able to enhance absorption of the NIR excitation energy and to improve the efficiency of energy transfer from Yb 3+ to RE 3+ for better luminescence . In practice, intense green UC emission from Ca 3 (Sc 2 Si 3 )O 12 :Yb/Tb, strong white emission from Lu 3 Ga 5 O 12 :Tm/Yb/Er, intense NIR Stokes and blue anti‐Stokes emissions from Lu 3 Ga 5 O 12 :Yb/Tm, dominantly strong red emission from (Gd 1‐ x Lu x )AG:Yb/Ho ( x = 0.1‐0.5), green and red luminescence from YAG:Yb/Er, and absolutely strong NIR emission from Ca 3 Ga 2 Ge 3 O 12 :Cr/Yb/Tm garnets have been reported.…”