Size-Dependent Upconversion Luminescence in Er³⁺/Yb³⁺-Codoped Nanocrystalline Yttria:  Saturation and Thermal Effects

Abstract

In this paper, the upconversion luminescent properties of Y2O3:Er3+(1%)/Yb3+(4%) nanoparticles with different sizes (13−55 nm) and its corresponding bulk material as a function of excitation power were studied under 978-nm excitation. Red (4F9/2 → 4I15/2), green (2H11/2, 4S3/2 → 4I15/2), and blue (2H9/2 → 4I15/2) transitions were observed. The results indicated that the relative intensity of the blue as well as the red to the green increased gradually with decreasing particle size. As a function of excitation power, the slope in the ln−ln plot for the red emission changed between 2.0 and 1.0 and gradually decreased with increasing particle size, which was attributed to competition between linear decay and upconversion processes for the depletion of the intermediate excited states. As the particle size decreased to 13 nm, a three-photon populating process occurred for the green emission. As the excitation power varied in different paths, gradually increasing or gradually decreasing, a hysteresis loop appeared in the power dependence of emission intensity, which was mainly caused by a local thermal effect induced by laser irradiation. The intensity ratio of 2H11/2 → 4I15/2 to 4S3/2 → 4I15/2 (R HS ) varied complicatedly with excitation power, which was theoretically explained considering the thermal distribution and relaxation processes. Two novel cross-relaxation paths were proposed on the basis of the variation of R HS under excitation at different wavelengths, 488 and 978 nm.

Excitation energy migration dynamics in upconversion nanomaterials

“…Yb 3+ ) have similar properties. The ''long-range'' energy transfer of Yb 3+ was supported by the strong upconversion emission of core-active shell structures, 10,12,13 especially by the Nd 3+ -sensitized NaYF 4 :Yb 3+ ,Er 3+ @NaYF 4 :Yb 3+ @NaYF 4 :Yb 3+ ,Nd 3+ core-shell-shell structure designed by Zhong et al, as shown in Fig. 6.…”

“…For example, enhancement and/or broadening of the absorption can be realized by anchoring organic molecules or other light harvesting entities onto the surface of upconversion nanoparticles. In addition, the highfrequency vibrational modes of surfactants and/or other organic entities on the surface are widely acknowledged to assist the population relaxation between the two electronic states of the activators/sensitizers inside the nanoparticles, 3,4 although the interaction mechanism remains vague.…”

Fabrication of ordered magnetite-doped rare earth fluoride nanotube arrays by nanocrystal self-assembly

“…Furthermore, the emission ratio of red to green photons greatly increases for the magnetite-doped nanotubes (Fe 3 O 4 ReF-NTs). This can be ascribed to the effect of O and Fe on the UC emission population, which has been explained by a cross-relaxation process [15,43].…”

“…As the particle size decreases, the ratio of surface to volume increases, and the number of surface defects with available large vibrational modes Nano Research such as those of anions increases, resulting in a great increase in nonradiative relaxation [42,43]. Thus, high efficiencies are observed.…”

Local Field Modulation Induced Three‐Order Upconversion Enhancement: Combining Surface Plasmon Effect and Photonic Crystal Effect

“…Actually, the apparently inverted R G/R after the introduction of AuNRs can be also attributed to the thermal conversion and conduction induced by SPR absorption of AuNRs, which leads to the increase of nonradiative relaxation channels of 4 I 11/2 -4 I 13/2 as well as 4 S 3/2 -4 I 9/2 . [ 33 ] To precisely understand the intensity enhancement on the SPPC structure, we simulated the | E | 2 surrounding isolated AuNR, AuNRs fi lm, OPCs, and AuNRs/OPCs hybrids under the excitation of 980 nm, as shown in Figure 3 e-h. It is clear that the | E | 2 of an isolated AuNR is concentrated on the vicinity of the rod tips, with a maximum intensity enhancement of 70 times at the hot spots.…”