Synthesis of new red phosphors with a smart material as a host material
The valence of Mn changes from 4 to 3 under various conditions
2021-07-20
(Press-News.org) Overview:
Professor Hiromi Nakano of Toyohashi University of Technology used a material with a unique periodical structure (smart material: Li-M-Ti-O [M = Nb or Ta]) as a host material to synthesize new Mn4+-activated phosphors that exhibit red light emissions at 685 nm when excited at 493 nm. Because the valence of the Mn ions in the material changes from Mn4+ to Mn3+ according to the sintering temperature, composition, and crystal structure, there is a difference in the photoluminescence intensity of the phosphors. XRD, TEM, and XANES were used to clarify the relationship between the photoluminescence intensity and the sintering temperature, composition, crystal structure, and MgO co-doping.
Details:
The white color in white LEDs is usually achieved by exciting a yellow phosphor with blue light. However, the color rendering index with this method is assessed as low because there is insufficient red light when compared to sunlight. Therefore, phosphors that emit red light have an important role as materials with a high color rendering index.
Previously, Professor Nakano's team used a smart material (Li-M-Ti-O [M = Nb or Ta]) as a host material to synthesize an Eu3+-activated red phosphor. This time, they synthesized new Mn4+-activated red phosphors without using rare earth materials.
The Li-Nb-Ti-O (LNT) system and Li-Ta-Ti-O (LTT) system are both smart materials (see figure for example) that self-organize into a periodical structure with an intergrowth layer period that changes according to the TiO2 doping amount. The periodical structure area of the LTT system is narrower than that of the LNT system, and there is a difference in the sintering conditions for its creation. Therefore, while comparing the LNT and LTT systems, the team closely investigated how photoluminescence intensity and Mn ion valence change with the sintering temperature, composition, crystal structure, and MgO co-doping.
As a result of this research, it was understood that LTT had notably higher photoluminescence intensity than LNT because of changes in the crystal structure due to the sintering temperature and composition. Generally, if the sintering temperature is high, Mn4+ will likely reduce to Mn3+, explaining the decrease in the photoluminescence intensity. In regards to changes in the crystal structure, when the TiO2 doping amount is increased, the number of [Ti2O3]2+ periodical intergrowth layers also increases. Because the intergrowth layer is formed with Ti3+ ions, it was understood that the surrounding oxygen deficiencies contribute to reductions from Mn4+ to Mn3+. Additionally, when MgO doping was performed to increase the photoluminescence intensity, the LTT phosphor that did not have a periodical structure exhibited a 100% Mn4+ ratio and the highest photoluminescence intensity.
Development Background:
The student who was initially involved in the experiment stated that "the Mn4+ phosphor did not exhibit photoluminescence with the host material", and the research was put on hold for about six months. Next year, a different student synthesized the phosphor and stated, "it exhibits a weak photoluminescence, but I think we could try some things to improve it." Through repeated trial and error, the team uncovered an important factor: in addition to the sintering temperature, there were significant differences in the changes to the crystal structure when the Mn4+ ratio was controlled. Through numerous trips to the Aichi Synchrotron Radiation Center, the team was able to measure the Mn4+ ratio and consolidate their research results.
Future Outlook:
The Mn4+-activated phosphor had to be synthesized at a comparatively low 850 °C in order to increase the Mn4+ ratio. However, under this condition, there is an issue with moderately low crystallinity. In the future, they will try various co-dopants to further explore the synthesis process to achieve a brighter red phosphor. In recent years, there has been more interest in deep-red Mn phosphors activated without the use of rare-earth materials, such as for use in LED grow lights, and applications can be expected to expand in the future.
INFORMATION:
Reference:
Hiromi Nakano, Shota Ando (2021) "Relationship between photoluminescence intensity, Mn ion oxidation, and crystal structure of new phosphors Li-M-Ti-O:Mn4+ (M = Nb or Ta)" Materials Research Bulletin vol. 143, pp. 111445 (1-7). https://doi.org/10.1016/j.materresbull.2021.111445
[Attachments] See images for this press release:
ELSE PRESS RELEASES FROM THIS DATE:
2021-07-20
Chinese researchers along with international colleagues recently reported a 6,700-year-long, precisely dated and well-calibrated tree-ring stable isotope chronology from the Northeastern Tibetan Plateau. It reveals full-frequency precipitation variability in the Asian Summer Monsoon (ASM) from interannual to multimillennial timescales with a long-term decreasing trend and several abrupt climate change events.
The international research team comprised 20 scientists from research groups based in China, Norway, Germany, United Kingdom, USA, Sweden, Canada, and Switzerland ...
2021-07-20
Tokyo, Japan - While researchers have known for years that immunoglobulin A (IgA) is important for gut health, it has remained unclear exactly what role it plays in preventing infection and disease. But now, researchers from Japan have found that eliminating IgA disrupts the balance of the intestinal ecosystem, making it susceptible to disease.
In a study published online in May in Gut, researchers from Tokyo Medical and Dental University (TMDU) have revealed that IgA deficiency results in substantial inflammation of the ileum, a specific part of the small intestine.
IgA is present in large quantities in the small intestine, where it helps protect the body against microorganisms that could potentially cross the lining of the gut to cause ...
2021-07-20
A new study by a team of researchers has found that the consolidation of traditional smallholder farms in China has a devastating effect on the biodiversity of wild pollinators in the area.
Pollinators play an essential role when it comes to supporting global food production.
However, wild pollinators are on the decline for several reasons, including the loss of floral resources and nesting sites. This loss of biodiversity could have far-reaching consequences for global food production in future.
"Biodiversity is essential for all life, with pollinators being one of the most important groups," says Dr Yi Zou from Xi'an Jiaotong-Liverpool ...
2021-07-20
CORVALLIS, Ore. - A 17-year study in Oregon, Washington and California found that removal of invasive barred owls arrested the population decline of the northern spotted owl, a native species threatened by invading barred owls and the loss of old-forest habitats.
The conservation and management of northern spotted owls became one of the largest and most visible wildlife conservation issues in United States history after the U.S. Fish and Wildlife Service listed the spotted owl as threatened under the Endangered Species Act in 1990 because of rapid declines in the owl's old-forest habitats. Four years later, the Northwest Forest Plan was adopted and reduced the rate of logging of old-growth forests on federal lands.
Despite more ...
2021-07-20
Tsukuba, Japan - Scientists from the department of Anatomy and Embryology at the Faculty of Medicine of the University of Tsukuba created a computer model to simulate the development of complex structures based on the Delta-Notch signaling pathway. This work may lead to a more comprehensive picture of the process that results in the formation of organs and other physiological systems.
The development of a tiny embryo consisting of undifferentiated cells into a healthy fetus with spatially defined organs depends on the complex interplay between genetic instructions and signaling molecules. For example, "Notch" genes are ...
2021-07-20
Berkeley -- More than 700 imaging satellites are orbiting the earth, and every day they beam vast oceans of information -- including data that reflects climate change, health and poverty -- to databases on the ground. There's just one problem: While the geospatial data could help researchers and policymakers address critical challenges, only those with considerable wealth and expertise can access it.
Now, a team based at the University of California, Berkeley, has devised a machine learning system to tap the problem-solving potential of satellite imaging, using low-cost, ...
2021-07-20
CATONSVILLE, MD, July 20, 2021 - Uber and Lyft are popular on-demand ways to travel, but does that mean trains and buses are a thing of the past? Travelers prefer different modes of transportation at different times. So how can all these modes co-exist and do so successfully? New research in the INFORMS Journal Transportation Science has created a model and an algorithm to redistribute transit resources based on commuter preferences resulting in millions in savings.
"Based on case study experiments in New York City, our optimized transit schedules consistently lead to 0.4%-3% system-wide cost reduction. This amounts to rush hour savings of millions of dollars per day, while simultaneously reducing costs to passengers and transportation service ...
2021-07-20
A team of chemists from the Croatian Ruđer Bošković Institute (RBI) described a new, easy-to-use method for uninterrupted monitoring of mechanochemical reactions. These reactions are conducted in closed milling devices, so in order to monitor the reaction one has to open the reaction vessel, thus interfering with the process. The new method uses Raman spectroscopy to get deeper insight into solid-state milling reactions, without the usual interruption of the chemical reaction process.
Mechanochemical synthesis by milling is used today to prepare all ...
2021-07-20
High school students who participated in summer programs about public health increased their interest in pursuing careers in science, technology, engineering and mathematics (STEM), according to a Rutgers study.
Published in the journalPedagogy in Health Promotion, the study explored whether increasing public health awareness would motivate high school students to pursue public health careers.
Researchers found that the summer program, Public Health: Outbreaks, Communities, and Urban Studies (PHocus) offered in 2018 and 2019 increased the students' knowledge in public health, epidemiology, urban public health and global public health.
"Including interdisciplinary, authentic ...
2021-07-20
ROCHESTER, Minn. ? Using data from 9,859 COVID-19 infections, Mayo Clinic researchers have new insights into risk factors for younger populations, some of which differ significantly from their older counterparts. People younger than 45 had a greater than threefold increased risk of severe infection if they had cancer or heart disease, or blood, neurologic or endocrine disorders, the research found. These associations were weaker in older age groups. The study was published in Mayo Clinic Proceedings.
The research team studied people living in a 27-county region of Southeast Minnesota and West Central Wisconsin surrounding Mayo Clinic in Rochester diagnosed with COVID-19 between March and ...
LAST 30 PRESS RELEASES:
[Press-News.org] Synthesis of new red phosphors with a smart material as a host material
The valence of Mn changes from 4 to 3 under various conditions
