The principle of upconversion involves a nonlinear optical process where low-energy photons, typically in the infrared or near-infrared range, are absorbed by certain materials and converted to higher energy photons, such as visible or ultraviolet light. This process occurs by the sequential absorption of several lower energy photons by the material’s electrons, followed by the emission of a single higher energy photon.
This phenomenon relies on specific energy levels and electronic transitions in the material, often involving rare earth ions doped into host matrices like crystals or nanoparticles. The upconversion efficiency depends on factors such as excitation wavelength, doping concentration, and crystal structure of the material.
UP-Control conversion finds use in various applications across the optical, photonic and biomedical fields.
In optics, upconversion materials are used to convert infrared light to visible light, which improves the sensitivity of imaging and detection systems operating in the near-infrared spectrum. In photonics, upscaling is used to improve the efficiency of photovoltaic devices by allowing the harvesting of infrared light that conventional solar cells cannot absorb.
In biomedical sciences, upscaling is crucial for bioimaging applications, where it allows deeper tissue penetration and reduced autofluorescence compared to traditional fluorescence imaging techniques.
Upconversion mechanisms involve a series of energy transfer processes and electronic transitions in the upconversion material. Typically, upconversion occurs through a multiphotonal absorption process where two or more low-energy photons are sequentially absorbed by the material’s electrons.
This excites the electrons to higher energy levels, followed by nonradiative relaxation steps and subsequent single photon emissions with higher energy than the absorbed photons. The efficiency and spectral characteristics of the upconversion are determined by the energy level structure of the material, the dopant concentration, and the excitation conditions.
Cross-conversion nanoparticles (UCNPs) operate based on the principles of up-conversion, using nanoscale particles embedded with asulco conversion materials.
These nanoparticles absorb infrared or near-infrared light, which can penetrate deep into biological tissues and convert it into easily detectable visible or ultraviolet light. UCNPs typically consist of a shell-to-core structure where the core contains rare earth ions (e.g., erbium, ytterbium) doped into a crystalline matrix (e.g., Nayf4), and the shell provides stability and functionalization for specific applications.
Upon excitation with infrared light, UCNPs emit visible light, enabling enhanced imaging and sensing capabilities in biological and medical research.
The properties of upconversion nanoparticles include their ability to efficiently convert low-energy photons to higher-energy photons, which is crucial for applications requiring sensitive sensing and imaging. UCNPs exhibit sharp emission peaks, enabling multiplexed detection by tuning their composition and doping levels to emit light at different wavelengths.
They have low toxicity and good biocompatibility, making them suitable for biological applications such as bioimaging, biosensing and targeted drug delivery. UCNPs also provide photostability, enabling prolonged imaging sessions without significant degradation of fluorescence intensity, which is beneficial for long-term biological studies and medical diagnostics