Solvothermal nanoYAG synthesis: Mechanism and particle growth kinetics

In Situ TEM/STEM Investigation of Crystallization in Y3Al5O12:Ce at High Temperatures Inside a Transmission Electron Microscope

Y3Al5O12:Ce (YAG:Ce) phosphors are extensively used in the field of white light-emitting diodes (LEDs) due to their efficient luminescent properties. To optimize the performance of YAG:Ce phosphors, a comprehensive understanding of their synthesis and structural evolution is essential. This paper presents a direct in situ transmission electron microscopy (TEM) /scanning TEM (STEM) investigation on the transformation process of a precursor comprising nanocrystalline CeO2 dispersed in an amorphous Y-Al oxide matrix into crystalline YAG:Ce particles. The study reveals that nanocrystalline CeO2 particles dissolve completely in the Y-Al oxide matrix at a temperature above 900 °C, while YAlO3 (YAP)-type crystalline particles with Al2O3 phase in grain boundaries are observed above 1000 °C. Finally, YAG:Ce-type crystalline particles are formed above 1180 °C. Atomic-resolution energy-dispersive X-ray spectroscopy (EDS) elemental mapping demonstrates that the doped cerium (Ce) atoms occupy the same atomic sites as yttrium (Y). Photoluminescence measurements validate the efficient luminescent properties of the obtained YAG:Ce phosphor.

Glycothermal synthesis and photoluminescence of Mg-Si modified Ce:YAG nanophosphors

The absorption spectrum of Ce in a YAG based host grown using the glycothermal method was modified using the addition of Mg-Si pairs. Photoluminescence intensity was dramatically improved by increasing the reaction temperature to 315 °C instead of the conventionally used 300 °C. It was found that Mg acetate and tetraethylorthosilicate (TEOS) are suitable as precursors for the glycothermal process, as EDS elemental mapping showed their homogeneous inclusion in the final product. Their addition only slightly modified the emission spectrum of Ce:YAG. It was found that increasing the reaction temperature to 315 °C yielded nanoparticles 56 ± 16 nm in size with a 3.3× enhancement in absorption and 3.7× enhancement in emission intensities compared to samples synthesized at 300 °C, and an increase in photoluminescence quantum yield from 32% to 48%. Reaction kinetics of the precursors and a proposed route for post-synthesis surface functionalization are discussed.

Nd3+ doped Gd3Sc2Al3O12 nanoparticles: towards efficient nanoprobes for temperature sensing

Development of contactless temperature-probing nanoplatforms based on thermosensitive near-infrared (NIR) light-emitting nanoparticles opens up new horizons for biomedical theranostics at a deep tissue level. Here, we report on the crystallinity and relative thermal sensitivity of NIR emitting Nd³⁺ doped Gd₃Sc₂Al₃O₁₂ (GSAG:Nd³⁺) nanoparticles synthesized by a solvothermal method. The obtained nanoparticles are well-crystallized, with sizes less than 100 nm, and can be dispersed in water without any additional functionalization. Upon excitation at 806 nm, the nanoparticles exhibit emission in the first and second biological optical transparency windows. The temperature sensing properties were evaluated from the luminescence intensity ratio of the thermally coupled emission lines corresponding to the R₁, R₂→Z₅ transitions between the Stark sublevels of the ⁴F_3/2 and ⁴I_9/2 electronic states of Nd³⁺ in the physiological temperature range of 20-50 °C. GSAG:Nd³⁺ nanoparticles exhibit a maximal relative thermal sensitivity of 0.20% °C^-1, higher than that of YAG:Nd³⁺ nanoparticles used as a control, due to the difference in the crystal field of the host matrices. A higher synthesis temperature in the range of 300-400 °C was also provided to improve the crystallinity of the GSAG:Nd³⁺ nanoparticles which results in a higher relative thermal sensitivity. Our results demonstrate the potential of GSAG:Nd³⁺ nanoparticles as luminescence nanothermometers and emphasize the interest of the GSAG matrix itself, which with the presence of Gd, could lead to multimodal diagnostic applications in nanothermometry and magnetic resonance imaging (MRI).

Non-conventional Ce:YAG nanostructures via urea complexes

Ce:YAG nanostructures (Ce:YAG = Cerium in Yttrium Aluminium Garnet), easy to control and shape, have been prepared via templating approach using natural and synthetic materials (i.e. paper, cotton wool and glass wool) previously soaked with a gel-like metals precursor and then thermally treated to achieve the wished morphology. The final material, otherwise difficult to process, can be easily moulded, it is lightweight, portable and forms, at the nanoscale, homogeneous layers of interconnected but not agglomerated nanoparticles (15 ± 5 nm). Using the same synthetic route, called Urea-Glass-Route, but in absence of a template, extremely pure Ce:YAG nanoparticle (45 ± 5 nm) can be also prepared, highly crystalline and well-defined in size and shape. Both structural and optical properties of the final materials were investigated, showing high optical quality. The support allows the production of a multifunctional material with mouldable shape and potential lighting application for large structures combining the strength, chemical durability, fire resistance, and translucency of glass fibres. Last, but not least, the synthetic path also allows an easy scaling up of the process: the first, key step for practical application of nanosized rare-earth doped YAG on large scale.

A new solvothermal method for the synthesis of size-controlled YAG:Ce single-nanocrystals

This modified solvothermal method, combined with in situ photoluminescence measurements, allows the synthesis of well-crystallized size-controlled YAG:Ce nanocrystals.