Rare Earth Upconversion nanoparticles (UCNPs) are a type of material that emits high-energy photons by absorbing two or more low-energy photons caused by the anti-stokes process. It can emit ultraviolet (UV) visible light or near-infrared (NIR) luminescence upon NIR light excitation. Due to its excellent physical and chemical properties, including exceptional optical stability, narrow emission band, enormous Anti-Stokes spectral shift, high light penetration in biological tissues, long luminescent lifetime, and a high signal-to-noise ratio, it shows a prodigious application potential for bio-imaging and photodynamic therapy. This paper will briefly introduce the physical mechanism of upconversion luminescence (UCL) and focus on their research progress and achievements in bio-imaging, bio-detection, and photodynamic therapy.

Halide perovskite solar cells (PSCs) are considered as one of the most promising candidates for the next generation solar cells as their power conversion efficiency (PCE) has rapidly increased up to 25.2%. However, the most efficient halide perovskite materials all contain toxic lead. Replacing the lead cation with environmentally friendly tin (Sn) is proposed as an important alternative. Today, the inferior performance of Sn-based PSCs mainly due to two challenging issues, namely the facile oxidation of Sn²⁺ to Sn⁴⁺ and the low formation energies of Sn vacancies. Two-dimensional (2D) halide perovskite, in which the large sized organic cations confine the corner sharing BX₆ octahedra, exhibits higher formation energy than that of three-dimensional (3D) structure halide perovskite. The approach of mixing a small amount of 2D into 3D Sn-based perovskites was demonstrated as an efficient method to produce high performance perovskite films. In this review, we first provide an overview of key points for making high performance PSCs. Then we give an introduction to the physical parameters of 3D ASnX₃ (MA⁺, FA⁺, and Cs⁺) perovskite and a photovoltaic device based on them, followed by an overview of 2D/3D halide perovskites based on ASnX₃ (MA⁺ and FA⁺) and their optoelectronic applications. The current challenges and a future outlook of Sn-based PSCs are discussed in the end. This review will give readers a better understanding of the 2D/3D Sn-based PSCs.

Green emitting long afterglow phosphor SrAl₂O₄: Eu²⁺, Dy³⁺ was synthesized via the combustion method. The physical phase analysis was carried out by X-ray diffraction, the results show that the introduction of Eu²⁺ into the lattice of the matrix resulted in a broad green emission centered at 508 nm, which is ascribed to the characteristic 4f⁶5d¹ to 4f⁷ electronic dipole allowed transition of Eu²⁺ ions. The doping of Eu²⁺ and Dy³⁺ did not change the physical phase of the crystals. Dy³⁺, as a coactivator, does not emit light itself, but can generate holes to form a trap energy level, which acts as an electron trap center to capture some of the electrons generated by the excitation of Eu²⁺. After excitation has ceased, let them gradually to transfer to the ground state for long afterglow luminescence. Then, we investigate the optical characterizations of different samples excited by X-ray. We found that SrAl₂O₄: Eu²⁺, 0.5% Dy³⁺ has this higher luminous intensity and afterglow. Its fluorescence lifetime is about 720 ns, and its quantum yield can reach 15.18%. Through search engine marketing (SEM) and energy dispersive X-ray spectroscopy (EDX), it has been proved that the sample has been successfully synthesized and its component content has been confirmed. The Eg value calculated from the diffuse reflectance spectrum is 4.61eV. The prepared SrAl₂O₄: Eu²⁺, Dy³⁺ luminescent powder is combined with Polydimethylsiloxane substrate for anticounterfeiting application, which provides a novel idea and method for the development of the anticounterfeiting field.

A series of long-afterglow luminescent materials (SrAl₂O₄: Eu²⁺ (SAOE), SrAl₂O₄: Eu²⁺, Dy³⁺ (SAOED) and SrAl₂O₄: Eu²⁺, Dy³⁺, Gd³⁺ (SAOEDG)) was synthesized via the combustion method. Temperature and concentration control experiments were conducted on these materials to determine the optimal reaction temperature and ion doping concentration for each sample. The crystal structure and luminescent properties were analyzed via X-ray diffraction (XRD), photoluminescence (PL), and afterglow attenuation curves. The outcomes demonstrate that the kind of crystal structure and the location of the emission peak were unaffected by the addition of ions. The addition of Eu²⁺ to the matrix’s lattice caused a broad green emission with a central wavelength of 508 nm, which was attributed to the characteristic 4f⁶5d¹ to 4f⁷ electronic dipole, which allowed the transition of Eu²⁺ ions. While acting as sensitizers, Dy³⁺ and Gd³⁺ could produce holes to create a trap energy level, which served as an electron trap center to catch some of the electrons produced by the excitation of Eu²⁺ but did not itself emit light. After excitation ceased, this allowed them to gently transition to the ground state to produce long-afterglow luminescence. It was observed that with the addition of sensitizer ions, the luminous intensity of the sample increased, and the afterglow duration lengthened. The elemental structure and valence states of the doped ions were determined with an X-ray photoelectron spectrometer (XPS). Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to characterize the samples. The results show that the sample was synthesized successfully, and the type and content of ions in the fluorescent powder could be determined. The fluorescence lifetime, quantum yield, bandgap value, afterglow decay time, and coordinate position in the coherent infrared energy (CIE) diagram of the three best sample groups were then analyzed and compared. Combining the prepared phosphor with ink provides a new idea and method for the field of anti-counterfeiting through screen printing.

The dependence of device performance has been measured for solar cells using blends containing the conjugated polymer, poly (3-hexylthiophene) (P3HT) with two different functionalized electron acceptor commercially available [6,6]-phenyl C-60 butyric acid methyl ester (PC₆₀BM) and graphene derivative to increase the carrier mobility which was produced in this laboratory. Performance was characterized by short-circuit current–open circuit voltage output of the devices. The interrelationships between UV-Vis absorption, fill factor and energy conversion efficiency (ECE) have been simulated. It is observed that the ECE of the device with low concentration of solution-processable functionalized graphene (SPFGraphene) has been increased significantly compared with the device without SPFGraphene. The improved performance is attributed to the presence of semiconducting graphene which provides charge-transport pathways for carriers to be extracted and hence boosts carrier mobility in organic photovoltaic (OPVs) devices. However, when the concentration of SPFGraphenes increased up to certain degree, the performance of the device decreased. By analysis on the intensity dependent photocurrent, the decreased performance is attributed to the PC₆₀BM-graphene which causes bimolecular recombination of free carriers. In addition, the active layer films were also investigated by XRD and SEM in order to understand the crystallite and morphology of the hybrid films.