Upconversion lanthanide nanomaterials: basics introduction, synthesis approaches, mechanism and application in photodetector and photovoltaic devices

Enhanced response of an infrared photodetector based on hybridization between reduced graphene oxide and up-conversion microparticles

Infrared (IR) photodetectors play an important role in many fields such as industry, medicine, security, etc. Achieving high response and maintaining stability in the device performance while reducing materials cost are required for the practical use of optical sensors. This study presents the development of a low-cost but high-performance IR photodetector based on a hybridization of up-conversion microparticles of NaYF4:Tm,Yb (UCMPs) and reduced graphene oxide material (RGO). In this combination, UCMPs play the role of absorbing photons from 980 nm excitation light, generating electron-hole pairs, which are useful for sensing applications. Meanwhile, RGO acts as a charge collector or a charge transport layer because of its high mobility, good electro-conductivity, and large surface area. Through various characterization experiments in dark and light conditions, the analysis results confirm that our devices show sensitivity to IR light with excellent operation stability up to 30 days even stored in ambient conditions. Overall, the combination of UCMPs and RGO materials promises to increase the ability to absorb infrared light, the optical sensitivity of the photodetector.

Surface Plasmon-Driven Versatile Enhancement of Chemosensing

Chemo-sensors have deeply integrated into various facets of our daily lives. To further satisfy the increasing performance demand, the current attempts are mainly centered on materials science approaches, usually involving time-& labor-consuming structure designing, synthesis, and modification. To date, it remains largely unexplored to enhance sensing material performance at the fundamental physical level by strategic exploitation of optical properties. In this work, we proposed a facile and versatile approach for improving the material performance by strategically utilizing the surface plasmon resonance─a characteristic property of optical devices. This approach is revealed to have a dual effect on fluorescence-based chemosensing: it amplifies the collection of fluorescence signals and simultaneously expedites the kinetics of chemical reactions. In this work, we developed a surface plasmon-driven fluorescence-based chemosensor that utilizes the 2,4,6-trisformyl phenol-diethylamine (TFP-I) fluorescent probe for the detection of hydrogen peroxide (H2O2) gas molecules. By harnessing the dual-effect induced by surface plasmons, we achieved outstanding sensing performance for H2O2 gas molecules, characterized by 0.0225 ppt sensitivity and an exceedingly low limit of detection. This study substantiates the applicability of the surface plasmon resonance-based optical effect in the realm of fluorescent chemical materials for sensing performance amplification. Beyond this, it pioneers the strategic harnessing of optical effects to manipulate the performance of chemical materials, particularly for the advancement of sensing capabilities.

Fabrication of Europium-Doped CaF2 Films via Sol-Gel Synthesis as Down-Shifting Layers for Solar Cell Applications

In the present work, an in-depth study on the sol-gel process for the fabrication of Eu-doped CaF2 materials in the form of thin films has been addressed for the production of down-shifting layers. Fine-tuning of the operative parameters, such as the annealing temperature, substrate nature and doping ion percentage, has been finalized in order to obtain Eu(III)-doped CaF2 thin films via a reproducible and selective solution process for down-shifting applications. An accurate balance of such parameters allows for obtaining films with high uniformity in terms of both their structural and compositional features. The starting point of the synthesis is the use of a mixture of Ca(hfa)2•diglyme•H2O and Eu(hfa)3•diglyme adducts, with a suited ratio to produce 5%, 10% and 15% Eu-doped CaF2 films, in a water/ethanol solution. A full investigation of the structural, morphological and compositional features of the films, inspected using X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDX), respectively, has stated a correlation between the annealing temperature and the structural characteristics and morphology of the CaF2 thin films. Interestingly, crystalline CaF2 films are obtained at quite low temperatures of 350-400 °C. The down-shifting properties, validated by taking luminescence measurements under UV excitation, have allowed us to correlate the local environment in terms of the degree of symmetry around the europium ions with the relative doping ion percentages.