Ural scientists synthesized a new phosphor
Chemists and physicists from Ural Federal University and Institute of Chemistry of Solids of the Ural Branch of Russian Academy of Sciences synthesized a new compound and studied its properties. Derivative of compounds may be used to convert UV radiation into visible light and change laser radiation range. The work was published in Journal of Luminescence.
The article authors worked with lithium-containing compounds with garnet structure. The chemical formula of such compositions is LixLa3M2O12, where M is zirconium, niobium, tin, tellurium, hafnium, or tantalum and x equals three to seven. A greatest number of publications about materials based on these systems, such as a popular hafnium garnet Li7La3Hf2O12, have been published lately. However, their optical properties remained understudied.
From the previous publications chemists knew that many hafnium compounds had photo-, X-ray-, and radioluminescence, i.e. emitted their intrinsic radiation induced by visible light, X-rays, or ionizing radiation. Thus, cerium-doped hafnium garnet Ca3Hf2SiAlO12 phosphor shows a broad cyan emission under 400 nm excitation (on the border between visible and UV radiation). The authors of the work decided to synthesize lithium-containing cerium-doped hafnium garnet (Li7La3Hf2O12:Ce3+) to obtain one more composition that emits in the visible spectrum.
Synthesized the necessary compounds, chemists started to study its properties. Using X-ray diffraction, they found out the compound's structural characteristics. Microstructure was studied using scanning electron microscopy. To determine the relationship between reflection, excitation, and luminescence spectra on the dopant concentration and temperature, the chemists carried out complex analysis of optical spectroscopy. They managed to find a correlation between separate emission bands (small areas of the reflection spectrum) and F+ centers.
"After detailed analysis of all obtained characteristics and using EPR spectroscopy we managed to prove that the increase of cerium concentration led to the reduction in the intensity of photoluminescence associated with intrinsic luminescence centers in Li7La3Hf2O12 represented by excitons (quasiparticles as bound states of electron and hole) in regular crystal lattice nods (Hf-O)," said Yana Baklanova, a co-author of the article, and senior scientific associate of Institute of Chemistry of Solids of Ural Branch of Russian Academy of Sciences.
The compound with other dopants may be used in the manufacturing of medical and optic devices and monitoring systems,
"A Li7La3Hf2O12 compound doped with europium and neodymum or holmium (Eu3+ and Nd3+/Ho3+) may by used to convert UV radiation into the visible spectral range and monochromatic laser radiation – into infrared range with shortwave- and middle-infrared spectral range. IR radiation is widely used in medicine, various optical systems, and also for air pollution analysis," concluded Alexey Ishchenko, a co-author of the article, assistant professor and senior scientific associate of Ural Federal University.