Cross-Relaxation from Er³⁺(²H_11/2,⁴S_3/2) and Er³⁺(²H_9/2) in β-NaYF₄:Yb,Er and Implications for Modeling Upconversion Dynamics

Abstract

We have implemented both the Dornauf− Heber (D−H) model and a brute force statistical (BFS) model to characterize the quenching by neighboring Er and Yb ions of the green and blue emitting states of Er in β-NaYF 4 :Yb,Er@NaYF 4 nanoparticles. Each of these models explicitly considers the radial distribution of Er and Yb acceptors around the two crystallographically distinct types of Er donor sites out to a user-specified donor−acceptor (D−A) cutoff distance, R a , beyond which the acceptor distribution is approximated as a spatial continuum. An algorithm is proposed for the BFS model, which makes it tractable to deal with the enormous number of possible acceptor distributions around the donor sites. The two models are compared for the convergence of fit values of critical energy-transfer distances, R 0 , as a function of the D−A cutoff distance, R a , for switching to the continuum approximation. The D−H model requires a much higher R a value (R a ≫ R 0 ) to achieve convergence compared to BFS, primarily because of the specific mathematical construct of the D−H model. The BFS model achieves convergence at R a ≈ R 0 , indicating that, on a purely physical basis, the continuum approximation is acceptable for D−A separations larger than the critical energy transfer distance. Both models do, however, ultimately converge to similar R 0 values. Our analysis shows that the green emission from Er ions, which have other Er ions occupying nearest neighbor sites, is almost completely quenched. In modeling upconversion, this subpopulation of Er ions should be treated as "dark" quenching sites for Yb 3+ ( 2 F 5/2 ) excitation. For an 18% Yb, 2% Er doping composition, approximately 10% of Er ions are "dark".

An up-conversion luminophore with high quantum yield and brightness based on BaF2:Yb3+,Er3+ single crystals

“…This behaviour can be explained by two energy transfer processes ( Figure S2): (i) 4 F 7/2 ⟶ 4 I 11/2 which is resonant with the 4 I 15/2 ⟶ 4 I 11/2 transition ( Figure S2, transition ) and (ii) 4 F 5/2 ⟶ 4 F 9/2 which is resonant with the 4 I 15/2 ⟶ 4 I 13/2 transition ( Figure S2, transition ). 72 The contribution of the first energy transfer process can give the rise in the {Er 3+ : 4 I 11/2 & Yb 3+ : 2 F 5/2 } manifold emission. In its turn, the contribution of the second process can be responsible for increase of the relative intensity of the 4 F 9/2 level.…”

On the Fly” Characterization of YbIII:ErIII Co-Doped Upconversion Nanoparticle Nonlinear Optical Response from Single-Particle Trajectories

“…For example, complete parameterization of the energy-level shown in Figure 1 based on experimental results will require further spectroscopic studies of all the photophysical processes involved and lead to a better model for UCNPs with improved theoretical understanding of the photophysics. [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] For lanthanide-containing coordination complexes and clusters as well as smaller UCNPs, [47,48] the resulting faster diffusion will require new approaches, such as, for example, simulations incorporating ballistic dynamics combined with optical micro-spectroscopy experiments at higher frame rates. Furthermore, in such cases, the spectroscopic-stochastic dynamics may involve emitting quantum states in non-stationary populations, without clear timescale separation between photophysics and Brownian motion as shown here.…”

Synthesis and design of NaYF4 microprisms via a microwave‐assisted approach for highly sensitive optical thermometry applications

“…4 Fluoride based host materials including NaLnF 4 (Ln = Y, La, Gd, Lu) with venerable characteristics of lesser phonon energy and tunable morphology are mostly studied as the upconversion hosts. 5,6 To date, among the various host, NaYF 4 is regarded as the best upconversion matrix owing to the low phonon energy (~400 cm −1 ), elevated chemical stability, and a superior refractive index (~1.45). 7 It is well-known that NaYF 4 usually appears in two crystallographic structures, cubic (α) and hexagonal (β) phases, and the upconversion efficiency of the hexagonal polymorph is much higher than that of the cubic analog.…”

“…8 Therefore, great attention has been devoted to synthesize high-quality β-NaYF 4 materials of numerous shapes specially microrods, microspheres, microtubes, microplates, microprisms, etc., with uniform sizes. [1][2][3][4][5][6][7][8] Various microstructures of NaLnF 4 :Er 3+ /Yb 3+ upconversion phosphors are reported to be suitable in multifunctional stands for biomedical application. 9 According to Du et al, there subsists some opportunities for the enhancement of upconversion efficiency to meet their diversified applications.…”

“…6 Several research works have been reported on the altering of crystal field using the variation in electric/ magnetic field, doping with a transition metal, and rare-earth elements to enhance upconversion emission. [1][2][3][4][5][6] Yang et al have reported a facile approach to weaken the thermal quenching procedure for improving upconversion efficiency of Er 3+ -doped β-NaYF 4 nanocrystals via acidtreatment. 10 More exertions should be dedicated to find novel procedures to improve the upconversion performance of the fluorides.…”