Ultrabright single-band red upconversion luminescence in highly transparent fluorosilicate glass ceramics containing KMnF3 perovskite nanocrystals

Lead-Free Cesium Manganese Halide Nanocrystals Embedded Glasses for X-Ray Imaging

The toxicity of heavy-metal Pb and instability of lead-based halide perovskite nanomaterials are main factors to impede their practical applications in the fields of solar cells, LEDs and scintillators. In this paper, all inorganic lead-free cesium manganese halide nanocrystals are synthesized in glass for the first time. Red photoluminescence with broad PL band, negligible self-absorption and a high photoluminescence quantum yield of 41.8% is obtained. In addition, modulating halide component can change the Mn²⁺ ions coordination environment to obtain tunable photoluminescence from red to green. More importantly, cesium manganese halide nanocrystals embedded glasses exhibit outstanding long-term stabilities. Theses cesium manganese halide nanocrystals embedded glasses are also highly stable against high energy irradiation and exhibit highly efficient radioluminescence, making them promising for high-resolution X-ray imaging. These results demonstrate that cesium manganese halide nanocrystals embedded glasses are promising eco-friendly candidates for applications in light-emitting diodes and scintillators.

LiYF4-nanocrystal-embedded glass ceramics for upconversion: glass crystallization, optical thermometry and spectral conversion

Glass ceramics (GCs) can perfectly integrate nanocrystals (NCs) into bulk materials. Herein, GCs containing LiYF4 NCs were fabricated via a traditional melt-quenching method and subsequent glass crystallization. Structural characterization was carried out via X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and scanning transmission electron microscopy high-angle annular dark-field (STEM-HAADF) analysis, suggesting the precipitation of LiYF4 NCs from a glass matrix. Taking Eu3+ as a structural probe, the spectrographic features provide compelling evidence for the partition of dopants. In particular, intense upconversion (UC) emission was achieved when co-doped with Yb3+ and Er3+. Temperature-dependent UC emission behaviour was also established based on the fluorescence intensity ratio (FIR) of Er3+, to study its properties for optical thermometry. Furthermore, spectral conversion was attained through cross relaxation (CR) between Ce3+ and Ho3+, tuning from green to red with various Ce3+ doping concentrations. There is evidence that LiYF4 NC-embedded GCs were favorable for UC, which may be extremely promising for optical thermometry and spectral conversion applications. This work may open up new avenues for the exploration of GC materials for expansive applications.

Trapped excited electrons in Ni2+-doped perovskite KZnF3 nanocrystals in KF-ZnF2-SiO2 glass ceramics

The photonic properties of glass ceramics (GCs) are often enabled by encapsulating nanocrystals (NCs) and doped transition metal ions (TMIs). However, it is difficult to probe the optics-related effect between the host NCs' band structure and doped TMIs' d-d orbitals. Herein, perovskite-type KZnF₃:NiNCs in KF-ZnF₂-SiO₂ GCs were prepared and taken as a model system. The excited-state dynamics of host NCs and Ni ions' d-d orbitals were studied by transient absorption spectroscopy. It presents a strong interaction between Ni's d orbitals and the band edge, which could extract excitonic energy in photonic applications. These findings facilitate understanding and design of TMIs-doped GCs in real-life photonic applications.

Efficient green upconversion luminescence in highly crystallized ultratransparent nano-glass ceramics containing isotropic KY3F10 nanocrystals

Yb³⁺/Er³⁺ co-doped nano-glass ceramics (GCs) containing isotropic KY₃F₁₀ nanocrystals (NCs) are obtained from a simple ternary oxyfluoride glass by controlled crystallization. The nano-GCs thus obtained, albeit having very large crystallinity of ∼35%, are ultratransparent in the whole visible-light wavelength region of 300-700 nm. Remarkably enhanced green upconversion luminescence (UCL) of Er³⁺ (by 55 times) is observed in the nano-GCs as compared to the precursor glass. Absolute quantum efficiency of the green UCL reaches as high as 0.41±0.02% in the GCs under 10  W/cm² power density. The UCL efficiency is comparable to that of the famous ZBLAN: Yb³⁺/Er³⁺ glass and GCs containing β-NaYF₄:Yb³⁺/Er³⁺ NCs, and nearly twice as large as that of GCs containing KYF₄:Yb³⁺/Er³⁺ NCs under the same excitation conditions.