Local Structure Engineering in Lanthanide-Doped Nanocrystals for Tunable Upconversion Emissions

Abstract

Upconversion emissions from lanthanide-doped nanocrystals have sparked extensive research interests in nanophotonics, biomedicine, photovoltaics, photocatalysis, etc. Rational modulation of upconversion emissions is highly desirable to meet the requirements of specific applications. Among the diverse developed methods, local structure engineering is fundamentally feasible, through which the upconversion emission intensity, selectivity, wavelength shift, and lifetime can be tuned effectively. The underlying mechanism of the local-structure-dependent upconversion emissions lies in the degree of parity hybridization and energy level splitting of lanthanide ions as well as the interionic energy transfer efficiency. Over the past few years, there has been significant progress in local-structure-engineered upconversion emissions. In this Perspective, we first introduce the principles of upconversion emissions and typical characterization methods for local structure. Subsequently, we summarize recent achievements in tuning of upconversion emissions through local structure engineering, including host composition adjustment, external field regulation, and interfacial strain management. Finally, we propose a few perspectives that should tackle the current bottlenecks. This Perspective is expected to deepen the understanding of local-structure-dependent upconversion emissions and arouse adequate attention to the engineering of local structure for desired properties of inorganic nanocrystals.

Boosting Near‐Infrared Luminescence of Lanthanide in Cs2AgBiCl6 Double Perovskites via Breakdown of the Local Site Symmetry

“…Therefore, the local site symmetry of Bi 3+ would reduce in Cs 2 Ag 0.8 Na 0.2 BiCl 6 , which may be much lower than the symmetry of O h in Cs 2 AgBiCl 6 . These results provide theoretical evidence of the breakdown of local site symmetry in Cs 2 AgBiCl 6 : Yb 3+ DPs caused by the Na + doping, which thus promoted the absorption and excitation of Bi 3+ and the PLQY improvement of Ln 3+ ions [18] …”

“…These results provide theoretical evidence of the breakdown of local site symmetry in Cs 2 AgBiCl 6 : Yb 3 + DPs caused by the Na + doping, which thus promoted the absorption and excitation of Bi 3 + and the PLQY improvement of Ln 3 + ions. [18] In order to shed more light on the mechanism of luminescence enhancement of Yb 3 + and Er 3 + ions in Cs 2 Ag 1À x Na x BiCl 6 DPs upon Na + doping, we measured the Raman spectroscopy, which may reveal the structural evolution of Cs 2 Ag 1À x Na x BiCl 6 with Na + doping. Under the excitation of 532-nm laser, Cs 2 Ag 1À x Na x BiCl 6 : Yb 3 + samples exhibit three intense Raman modes (Figure 5c), corresponding to the breathing vibrations of Cl atoms (T 2g : 113 cm À 1 ), asymmetric stretching (E g : 216 cm À 1 ) and symmetric stretching (A 1g : 284 cm À 1 ) of AgÀ Cl bonds in the octahedral cages, respectively.…”

Exploiting the upconversion luminescence, Lewis acid catalytic and photothermal properties of lanthanide-based nanomaterials for chemical and polymerization reactions

“…Defects found in nanocrystals with poor crystalline quality and large surface-to-volume ratio can be prepared by tuning the synthesis parameters such as using lower reaction temperatures and shorter reaction times, and introducing extra dopant ions. 117…”

Simultaneous ultraviolet-C and near-infrared enhancement in heterogeneous lanthanide nanocrystals

“…13–16 These strategies combined with nanostructure engineering enabled a wide range of upconversion activators with emissions ranging from ultraviolet (UV) to near-infrared (NIR). 17,18…”

“…[13][14][15][16] These strategies combined with nanostructure engineering enabled a wide range of upconversion activators with emissions ranging from ultraviolet (UV) to near-infrared (NIR). 17,18 Despite the enriched emission profiles, their practical implementation in various applications is hindered by the limited emission intensity and the difficulty in shifting the emission wavelength to the ultraviolet-C (UVC, 100-290 nm) region. This is because photon upconversion from high-lying energy levels is significantly influenced by many deleterious factors, such as cross-relaxation between lanthanide ions, concentration quenching, and energy consumption induced by interior lattice defects.…”