Optical detection of cerium (Ce³⁺/Ce⁴⁺) ions in microparticles of yttrium aluminum garnet powder YAG:Ce³⁺ embedded free-standing composite films for narrowband blue to broadband visible light down-conversion

The search for more efficient ways to create both light sensors and VIS-IR sources has led to an ever-growing interest in coatings that convert UV radiation into white light. GaN LEDs with an emission wavelength of about 460 nm are most often used as UV emitters.

Step-down UV-converters often made from suspensions of rare-earth phosphor powders (e.g. cerium-activated yttrium-aluminum garnets YAG:Ce³⁺) for transformation of narrowband blue radiation into broadband VIS luminescent emission (540-590 nm). Depending on the technological process, the concentrations of trivalent Ce³⁺ ions and tetravalent Ce⁴⁺ ions in the yttrium aluminum garnet matrix change significantly. It is obvious that improving production technology is impossible without promptly measuring the concentration of Ce³⁺ ions in the transparent matrix, depending on the technological conditions of the synthesis.

The difficulty of experimentally determining the optical characteristics of films of optoelectronic converters is due to the fact that the phosphor composite is a classical turbid medium. Until now, in turbid media it is impossible to simply measure their most important optical parameters: when a light wave propagates in a turbid medium, its intensity gradually decreases due to scattering and absorption, the contribution of which to the extinction of light cannot be separated. Previously, we considered an original model approach and optimized composite production protocol to overcome ambiguity in experimental measurements, which makes it possible to determine the absorption of microcrystals in a phosphor-resin composition from the measured values of the transmittance of a set of films in a certain range of their thicknesses.

In this report, we examine an optical approach as well as design and contractions of physical sensing unit that allows the engineer to directly optimize the emission performance of optoelectronic UV downconverters for yttrium aluminum garnet powder doped with trivalent cerium (Ce³⁺) taking into account the turbidity of composite films.