What Is Beyond Charge Trapping in Semiconductor Nanoparticle Sensitized Dopant Photoluminescence?

Abstract

Yb] photoluminescence in doped tin dioxide [Sn(Ln)O 2 ] and doped titanium dioxide [Ti(Ln)O 2 ] nanoparticles shows that the emission efficiency of trivalent lanthanide cations (Ln 3+ ) in an oxide matrix can be improved by change of the cation site symmetry. An analysis of Ln 3+ emission quantum yield and asymmetry ratio is used to identify the importance of symmetry breaking around the dopant site for enhancing the Ln 3+ emission intensity. These findings identify an important criterion for engineering the luminescence intensity of dopant ions in semiconductor nanoparticle-based luminophores, which goes beyond the primary criterion of engineering the relative positions of the dopant energy levels with respect to the band edges of the host nanoparticle matrix.

Optimizing the Key Variables to Generate Host Sensitized Lanthanide Doped Semiconductor Nanoparticle Luminophores

“…For postsynthetically modified II–VI NPs energy dispersive X-ray spectroscopy (EDS) showed (a) incorporation of Ln in the NPs, (b) significant changes in anion content of the NPs, and (c) an absence of complete cation exchange which is consistent with thermodynamic expectations . While Ln 3+ emission is appreciable in semiconductor NPs with a concentration in the range of tens of micromolar, the same can only be realized with a millimolar concentration for their free salts. ,, Dramatically altered excitation profiles upon monitoring Ln 3+ emissions in NPs, which overlap with NPs electronic absorption spectra, ,,− ,,− demonstrate the sensitization of the Ln 3+ emission by the NP. The significant lengthening of Ln 3+ emission lifetime in the NPs, as opposed to their corresponding free Ln 3+ salts in bulk solvent, , and the spectral changes of the NP capping ligand’s IR absorption spectrum by Ln 3+ ,, further substantiate the incorporation of the Ln 3+ in the NP lattice.…”

“…(a) Steady-state photoluminescence emission spectra for the Ti­(Ln)­O 2 and Sn­(Eu)­O 2 NPs that display one dominant luminescent energy level, Ln = Nd, Sm, Eu and Yb. (b) The relative energy levels of the Ln 3+ ground and major luminescent energy levels (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Yb) are shown with respect to the valence and conduction bands of the host NPs (black dashed lines for TiO 2 and red dashed lines for SnO 2 ) (adapted with permission from ref , Copyright 2016 American Chemical Society and ref , Copyright 2018 American Chemical Society).…”

“…The Ln 3+ incorporation (in both synthetic and postsynthetic cases) has been demonstrated through observation of energy dispersive X-ray spectroscopic signatures for Ln 3+ in purified NPs, − and the increase in Ln 3+ photoluminescence in the NPs as compared to that found for free salts in bulk solvent. For postsynthetically modified II–VI NPs energy dispersive X-ray spectroscopy (EDS) showed (a) incorporation of Ln in the NPs, (b) significant changes in anion content of the NPs, and (c) an absence of complete cation exchange which is consistent with thermodynamic expectations .…”

Photoredox-Mediated Sensitization of Lanthanide Dopants by Perovskite Nanocrystals

“…An alternative explanation for the lack of emission of the Eu 3+ -doped NCs and the weak emission of the Sm 3+ -doped NCs is the nature of their emissive dipoles. The intraconfiguration f-f-based emission from Ln 3+* is driven by induced electric or magnetic dipole transitions . Yb 3+ has a permanent magnetic dipole, which induces an electric dipole that drives the emission, while Sm 3+ and Eu 3+ transitions ( 4 G 5/2 → 6 H 9/2 or 6 H 7/2 for Sm 3+ and 5 D 0 → 7 F 4 or 7 F 2 for Eu 3+ ) are mostly electric dipole-driven.…”

“…The intraconfiguration f-f-based emission from Ln 3+ * is driven by induced electric or magnetic dipole transitions. 30 Yb 3+ has a permanent magnetic dipole, which induces an electric dipole that drives the emission, while Sm 3+ and Eu 3+ transitions ( 4 G 5/2 → 6 H 9/2 or 6 H 7/2 for Sm 3+ and 5 D 0 → 7 F 4 or 7 F 2 for Eu 3+ ) are mostly electric dipole-driven. The ideal dopant site within the CsPbCl 3 lattice is highly symmetric, 15 which renders induced electric dipole-based emission formally forbidden.…”