Reversible Modulated Upconversion Luminescence of MoO3:Yb3+,Er3+ Thermochromic Phosphor for Switching Devices

Manipulation of Multimodal and Multicolor Luminescence via Interplay of Traps and Rare Earth Emission Centers in Calcium Tungstate

Multimodal luminescence involves color-tunable and wavelength manageable photon emissions upon variable luminescence pathways in response to different external stimuli, which provides clear visualization and high-level confidentiality for information encryption technologies. Integrating multimodal luminescence into a single matrix is regarded as a feasible strategy but remains a big challenge. In this work, multimodal (photoluminescence, persistent luminescence, upconversion luminescence, and thermally stimulated luminescence) and multicolor luminescence (green, yellow, orange, pink to red) is achieved in CaWO4:Yb3+,Er3+,Eu3+ phosphor by employing an interplay of traps and rare earth emission centers. Bright emission in a wide color gamut is achieved dynamically in response to thermal disturbance and light illumination, which further allows for on-demand emission manipulation in space and time dimensions. The compatible coexistence of multiple rare earth emissive centers together with abundant photoactive traps contributes to the excellent integration of multimodal photon emissions in calcium tungstate. This work provides a good example of integrating multimodal luminescence into one single matrix and indicates potential in advanced high-level information encryption applications.

Strong green upconversion emission from submicron spindle-shaped SrMoO4:Yb3+,Er3

Upconversion luminescence (UCL) is a fluorescence process where two or more lower-energy photons convert into a higher-energy photon. Lanthanide (Ln3+)-doped UCL materials often suffer from weak luminescence, especially when directly synthesized by a hydrothermal (HT) process due to the existing hydroxyl group and undesirable arrangement of dopants within host lattices which quench luminescence and limit energy transfer. Therefore, additional heat treatment processes are required to enhance their UCL emission, even though direct hydrothermal synthesis without further heat treatment has the advantages of low energy consumption, fast synthesis, and wide applicability to generate UCL materials. In this study, via a HT process without annealing, we have produced Yb3+ and Er3+ co-doped SrMoO4 submicron spindles with a strong green UCL emission which can be seen with the naked eye, which HT produced oxide-based UCL materials often fail to demonstrate. We have investigated different HT synthesis conditions, such as temperature, time, pH and dopant composition, which control the nucleation, growth, lattice structure arrangement, and ultimately their UCL properties through XRD, SEM, EDS and UCL measurements. The bright green UCL from the SrMoO4:Yb,Er submicron spindles is further enhanced by post-synthesis annealing within a molten NaNO3/KNO3 system to prevent particle size growth. The green UCL intensity from the annealed SrMoO4:Yb,Er submicron spindles surpasses samples produced by the solid-state method and is comparable to that from the commercial NaYF4:Yb,Er sample. We have further studied the temperature-dependent luminescence of both the HT-prepared and molten-salt annealed SrMoO4:Yb,Er submicron spindle samples. The strong UCL from our SrMoO4:Yb,Er submicron spindles could warrant their candidacy for bioimaging and anticounterfeiting applications.

Autocatalytic Laser Activator for Both UV and NIR Lasers: Preparation of Circuits on Polymer Substrates by Selective Metallization

In laser-induced selective metallization (LISM), conventional laser activators only work at a single laser wavelength. This study reported a new laser activator (MoO₃) very suitable for both 355 nm UV and 1064 nm near-infrared (NIR) lasers for the first time. When applying MoO₃ to polymers, the prepared Cu layer on laser-activated polymers showed a good conductivity (2.63 × 10⁶ Ω^-1·m^-1) and excellent adhesion. Scanning electron microscopy, optical microscopy, and resistance analysis revealed the excellent LISM performance of the polymer/MoO₃ composites, and the quality of the Cu layer prepared using the UV laser is much better than that using the NIR laser. The limit width of the copper wire prepared by the UV laser is as narrow as 30.1 μm. We also confirmed the mechanism of MoO₃ initiating electroless copper plating after laser activation to be the autocatalytic mechanism, which is very different from the conventional reduction mechanism. The effect of laser activation was only to expose the MoO₃ active species to the polymer surface. X-ray diffraction and tube experiments revealed that the activity of α·h-MoO₃ was higher than that of α-MoO₃. X-ray photoelectron spectroscopy indicated that a part of Mo⁶⁺ was reduced to Mo⁵⁺ during laser activations, leading to the increase of the oxygen vacancies in MoO₃ and possibly further enhancing the activity of MoO₃. Besides, the micro-rough structures caused by the laser on the polymer surface provided riveting points for successfully depositing the copper layer. The Ni-Cu, Ag-Cu, and Au-Ni-Cu layers were obtained via the continued deposit of other metals on the Cu layer. The resistances of these metal layers had much better stability than that of the neat Cu layer. Furthermore, the Au layer further enhanced the conductivity of the circuit. The proposed strategy is easy for large-scale industrial applications, which will greatly expand the application scenarios of the LISM field.

On enhancement and control of green emission of rare earth co-doped hydroxyapatite nanoparticles: synthesis and upconversion luminescence properties

In this work, low-temperature hydrothermal synthesis of a series of xMo–1%Er–10%Yb (x:mol%) doped hydroxyapatite (HA) phosphors was studied.

Novel Strategy for Designing Photochromic Ceramic: Reversible Upconversion Luminescence Modification and Optical Information Storage Application in the PbWO4:Yb3+, Er3+ Photochromic Ceramic

Inorganic photochromic material is an available medium to obtain optical information storage. The photochromic property of the inorganic material is mainly from the defects of the host. However, the formation of defects in the host is uncontrollable, in particular, the revisable formation and removement of defects are difficult. Thus, there are few inorganic materials with the revisable photochromism upon the entire light stimulation. Therefore, it is an urgent need to find a suitable approach to design inorganic photochromic materials. Here, the photochromic PbWO₄:Yb³⁺, Er³⁺ ceramic was designed with the help of valence state change of W⁶⁺ → W⁵⁺ and Pb²⁺ → Pb⁴⁺. Upon the 532 nm laser stimulation, the photochromism of the PbWO₄:Yb³⁺, Er³⁺ ceramic was obtained based on the Pb²⁺ + hν (532 nm) → Pb⁴⁺ + 2e^- and W⁶⁺ + e^- + hν (532 nm) → W⁵⁺ reaction, resulting in the optical information writing. Under the stimulation of an 808 nm laser, the written optical information was erased based on the W⁵⁺ + hν (808 nm) → W⁶⁺ + e^- and Pb⁴⁺ + 2e^- + hν (808 nm) → Pb²⁺ reaction. In addition, the photochromism-induced upconversion emission modification was obtained in the PbWO₄:Yb³⁺, Er³⁺ ceramic, realizing the effective and nondestructive reading out of optical information. The cyclic experiment demonstrated a good reproducibility of both photochromism and upconversion emission modification, exhibiting the potential application of the PbWO₄:Yb³⁺, Er³⁺ ceramic as the optical data storage medium.

Thermo-responsive light-emitting metal complexes and related materials

This review discusses the fundamentals and design strategies for the development of thermo-responsive metal–ligand coordination materials and the applications of these materials in temperature sensing, bioimaging, information security, etc.