Upconversion is widely used across various fields for its ability to convert low-energy photons, typically in the infrared or near-infrared spectrum, to higher energy photons such as visible or ultraviolet light. One of the main uses of upscaling is in biomedical imaging and sensing applications. By converting deep-penetrating near-infrared light into visible light, upconversion enables improved imaging depth and resolution in biological tissues.
This capability is crucial for non-invasive imaging techniques, diagnostics and targeted therapies where high sensitivity and spatial resolution are required. Additionally, upscaling is used in telecommunications, photovoltaics, and environmental monitoring for efficient light harvesting and data transmission.
The advantages of upscaling lie in its ability to harness infrared light, which can penetrate tissues and materials more effectively than visible light, and convert it into easily detectable higher energy photons.
This process improves sensitivity and reduces background noise in imaging and sensing applications. Upconversion materials also exhibit high photostability, allowing prolonged operation without significant degradation of fluorescence intensity. Additionally, positive conversion enables multiplexed detection by tuning the emission wavelengths of materials, enabling simultaneous detection of multiple targets or biomarkers in biological samples.
The main difference between cross-conversion and down-conversion is in the direction of photon energy conversion.
Upconversion involves converting lower energy photons (e.g., infrared) to higher energy photons (e.g., visible or ultraviolet) through a nonlinear optical process. This process typically requires several photon absorption and energy transfer steps in the material. In contrast, lower conversion converts higher energy photons to lower energy photons, such as converting ultraviolet light to visible light in phosphor materials or fluorescent dyes used in displays and lighting.
Down conversion processes are also used in fluorescence-based assays and imaging techniques where the emitted light is of lower energy than the absorbed excitation light.
Fluorescence upconversion refers to a specific technique where upconversion materials are used to convert infrared light into visible or ultraviolet light, which is then detected using fluorescence-based detection methods.
In this technique, nanoparticles or upconversion materials absorb two or more photons of lower energy (e.g., near infrared) and emit a single photon of higher energy (e.g., visible or ultraviolet) with characteristics of fluorescence. This enables sensitive sensing and imaging in biological and medical applications where deep tissue penetration and high spatial resolution are required.
Fluorescence positive conversion is advantageous for reducing autofluorescence and background compared to traditional fluorescence imaging techniques.
The photon positive conversion process involves several steps in upconversion materials. Initially, the upconversion material absorbs several lower energy photons simultaneously or sequentially, exciting electrons to higher energy states in the energy band structure of the material.
These excited electrons then undergo nonradiative relaxation processes to reach intermediate energy levels before emitting a single photon with higher energy than the absorbed photons. This emission process typically results in fluorescence or phosphorescence emission at specific wavelengths determined by material composition and energy levels. Photon conversion processes are nonlinear and depend on precise energy matching between photon energies and material bandgaps to achieve efficient conversion and emissions