Deyang Li

Rare-earth-doped fluoride nanoparticles (NPs), known for their tunable luminescence and high chemical stability, hold significant potential for applications in X-ray imaging and radiation dose monitoring. However, most research has primarily focused on lanthanide-doped NaLuF₄ or NaYF₄ nanosystems. In this work, Cs₂NaYF₆:Tb NPs with enhanced X-ray excited optical luminescence (XEOL) intensity were developed. Our results indicate that low oleic acid (OA) content and a high [Cs⁺]/[Na⁺] ratio favor the formation of pure cubic-phase Cs₂NaYF₆:Tb NPs. Cs₂NaYF₆:Tb NPs were successfully fabricated into thin films and employed as nanoscintillator screens for X-ray imaging, achieving a high spatial resolution of 20.0 Lp/mm. Beyond X-ray imaging applications, Cs₂NaYF₆:Tb NPs were also explored for spermine detection, demonstrating high sensitivity with a detection limit of 0.44 μM (under X-ray excitation) within a concentration range of 0–60 μM. These findings may contribute to the development of novel lanthanide-doped fluoride nanoscintillators for high-performance X-ray imaging and molecular sensing.

Near-infrared (NIR) luminescent phosphors hold promise for a wide range of applications, from bioimaging to light-emitting diodes (LEDs), but are typically confined to wavelengths 3+ (1540 nm), a 2.5-fold enhancement with increasing temperature from 298 to 356 K, from Yb³⁺- and Er³⁺-codoped CsPbCl₃ perovskite quantum dots (PQDs) (photoexcited at ∼365 nm). Mechanistic investigations revealed that thermally enhanced phenomena originated from combined effects of thermally stable cascade energy transfer (from a photoexcited exciton to a pair of Yb³⁺ and then to surrounding Er³⁺) and minimized quenching of surface-adsorbed water molecules on the ⁴I_13/2 state of Er³⁺ induced by the temperature increase. Importantly, these PQDs enable producing phosphor-converted LEDs emitting at 1540 nm with inherited thermally enhanced properties, having implications for a wide range of photonic applications.

Lead halide perovskites hold promise for photovoltaics, lasers, and light-emitting diode (LED) applications, being known as light-harvesting or -emitting materials. Here we show that colloidal lead halide CsPbCl3 perovskite quantum dots (PQDs), when incorporating divalent manganese (Mn2+) ions, are able to produce spin-paired singlet oxygen molecules with over-unit quantum yield (~1.08) in air condition. Our mechanistic studies and atomic-level density functional theory calculations endorse an energy-migration-mediated quantum cutting process favoring multiple singlet oxygen generation (MSOG), in which one exciton-activated bulk Mn2+ ion (~ 2.0 eV) inside the nanocrystal migrates its energy among the Mn2+ sub-lattice to two surface Mn2+ defect states (~ 1.0 eV), followed by nonradiative energy transfers to two surrounding oxygen molecules. Moreover, super-hydrophobicization of MOSG PQDs through silica-mediated polystyrene encapsulation prevents them from disintegration in aqueous medium, enabling photodegradation of methyl orange at a rate even higher than that of the canonical titanium oxide photocatalyst. The observation of ultra-efficient singlet oxygen generation in PQDs have implications for fields ranging from photodynamic therapy to photocatalytic applications.

The organic−inorganic hybrid perovskite solar cells (PSCs) have achieved rapid progresses in this decade. However, the limited solar spectral utilization has restricted the further improvement of performance for the PSCs. One promised approach on solving this problem is utilizing IR to visible upconversion nanoparticles (UCNPs) in the PSC devices. Despite, confined by the lower quantum yield and smaller absorption cross section of the traditional UCNPs, its application is still a great challenge. In this work, the IR-783 dye sensitized core/shell NaYF4:Yb3+, [email protected]:Yb3+, Nd3+ UCNPs, were synthesized and coupled with plasmonic Au nanorods (AuNRs) film. Thereby, the upconversion luminescence (UCL) intensity was enhanced about 120 folds, while the luminescent quantum yield (QY) was improved from 0.2% to 1.2%. Then, the composite UCNPs were assembled on the SnO2 layer of the PSCs, which resulted in the power conversion efficiency (PCE) increasing from 19.4% to 20.5% under simulated 100 mw/cm2 AM 1.5G irradiation. Up to now, it is the highest PCE for the PSCs based on various upconversion devices. Under the irradiation of sun concentrator (1 W/cm2), the PCE of the device can be further improved to 21.1%. The studies in depth indicate that under standard sunlight irradiation, the improvement of PCE is contributed by both the IR to visible UCL and the scattering effect of the UCNPs. Under irradiation of sun concentrator, the UCL contributes dominantly to the further improvement of PCE. This work provides an effective method on increasing the luminescent QY utilized in the PSCs and is of great significance to the future concentrating PSC devices.

The dearth of high upconversion luminescence (UCL) intensity at low excitation irradiance hinders the prevalent application of lanthanide-doped upconversion nanoparticles (UCNPs) in many fields ranging from optical bioimaging to photovoltaics. In this work, we propose to use microlens arrays (MLAs) as spatial light modulators to manipulate the distribution of excitation light fields in order to increase UCL, taking advantage of its nonlinear response to the excitation irradiance. We show that multicolored UCL from NaYF₄:Yb³⁺,Er³⁺@NaYF₄:Yb³⁺,Nd³⁺ and NaYF₄:Yb³⁺,Tm³⁺@NaYF₄:Yb³⁺,Nd³⁺ core/shell UCNPs can be increased by more than one order of magnitude under either 980 or 808 nm excitation, by simply placing a polymeric MLA onto the top of these samples. The observed typical green (525/540 nm) and red (654 nm) UCL bands from Er³⁺ and a blue (450/475 nm) UCL band from Tm³⁺ exhibit distinct enhancement factors due to their different multi-photon processes. Importantly, our ray tracing simulation reveals that the MLA is able to spatially confine the excitation light (980 and 808 nm) by orders of magnitude, thus amplifying UCL by more than 225-fold (the 450 nm UCL band of Tm³⁺) at low excitation irradiance. The proposed MLA method has immediate ramifications for the improved performance of all types of UCNP-based devices, such as UCNP-enhanced dye sensitized solar cells demonstrated here.

Dye-sensitized solar cells (DSSCs) have been deemed as promising alternatives to silicon solar cells for the conversion of clean sunlight energy into electricity.

The inability to utilize near infrared (NIR) light has posed a stringent limitation for the efficiencies of most single-junction photovoltaic cells such as dye-sensitized solar cells (DSSCs). Here, we describe a strategy to alleviate the NIR light harvesting problem by upconverting non-responsive NIR light in a broad spectral range (over 190 nm, 670–860 nm) to narrow solar-cell-responsive visible emissions through incorporated dye-sensitized upconversion nanoparticles (DSUCNPs). Unlike typically reported UCNPs with narrow and low NIR absorption, the organic dyes (IR783) anchored on the DSUCNP surface were able to harvest NIR photons broadly and efficiently, and then transfer the harvested energy to the inorganic UCNPs (typically reported), entailing an efficient visible upconversion. We show that the incorporation of DSUCNPs into the TiO₂ photoanode of a DSSC is able to elevate its efficiency from 7.573% to 8.568%, enhancing the power conversion efficiency by about 13.1%. We quantified that among the relative efficiency increase, 7.1% arose from the contribution of broad-band upconversion in DSUCNPs (about ∼3.4 times higher than the highest previously reported value of ∼2.1%), and 6.0% mainly from the scattering effect of DSUCNPs. Our strategy has immediate implications for the use of DSUCNPs to improve the performance of other types of photovoltaic devices.