Current Research Projects


Searching for Novel, Efficient Phosphors for use in Solid-State White Lighting Devices

The development of LED technology provides an opportunity of creating alternative light sources that are more efficient and longer lasting than traditional lighting. LEDs are used as indicator lights, turn signals, and as backlighting for screens. However, major energy savings will occur when this technology is used for in-home lighting. The most common method of creating a LED-based light bulb capable of in-home use is to use an LED light and inorganic phosphors (a material that absorbs and emits light). The phosphor absorbs the blue or near-UV LED emission and re-emits light at longer wavelength (yellow). The combination of emission from the LED and phosphor creates the appearance of white light, illustrated on the right. Currently, a majority of phosphors used for white light generation lack emission in the red region of the visible spectrum causing most bulbs to produce a "cool" (blue-ish) light that is harsh to the human eye. Furthermore, the efficiency of the phosphors decreases as the operating temperature of the LED increases.

The Brgoch group develops novel phosphors based on oxide, oxynitride, and nitride materials that overcome many of these issues. We focus on using a numerous synthetic methods such as high-temperature reaction, rapid microwave-assisted reactions, and sol-gel chemistry to prepare the materials. The characterization of new phosphors involves X-ray and neutron diffraction as well as optical spectroscopy. The group also employs computation to interpret the efficiency as well as temperature dependent optical properties of our new materials

A brief overview of our recent achievements can be found here.

 

 

Solid-state lights appear white because they use a phosphor powder to convert the emission from a LED chip. However, the optical properties of current phosphors are not robust at high temperatures and can produce a blue tinted light that is annoying. The Brgoch group is working to fix this problem by improving phosphors.

Targeting earth abundant superhard materials with big data

A majority of the known inorganic superhard materials contain expensive 4d or 5d transition metals, such as Ru, Rh, Os, Re, Ir and boron. Although these materials show excellent mechanical properties, their widespread application is currently limited due to extreme conditions required to prepare the materials as well as cost of the raw starting materials. In fact, specialized synthetic equipment is required because the starting materials are refractory metals with melting points often >2000°C. Thus, for any wide scale application of superhard materials the synthetic conditions and prohibitive cost need to be addressed.

In the Brgoch group, we are developing new superhard materials that require less challenging processing conditions and contain a larger percentage of earth-abundant starting materials. Specifically our research is focusing on:

— Analyzing the mechanical properties of known compounds using techniques borrowed from our colleagues in data mining to identify correlations. First-principles (DFT) calculations will be employed to determine additional metrics that should correlate with hardness, e.g., total bond strength. This will allow us to develop a set of “design rules” that will direct our experimental preparation.

— New materials will be prepared using an innovative microwave-assisted preparation route. This method allows a rapid screening of new compositions using a fraction of the power necessary for arc-melting. All of the materials will be characterized using micro-indentation, X-ray diffraction, solid-state NMR, and powder neutron diffraction.

Funded by:

(55625-DNI10) (NSF CMMI 15-62142)

 



Analyzing large data sets is a unique approach to identify trends among multiple, unrelated classes of materials. This approach allows our group to efficiently target compounds with an optimal mechanical response required for the development of novel superhard materials.

Uncovering the fascinating chemistry of anionic gold (Au) and platinum (Pt2−)

The unique properties of bulk solids stems from the connection between the composition and structure. Accordingly, it is important to continually search for compositions that produce novel and peculiar structures. One area that has remained relatively unexplored involves transition metal ions that are anionic, rather than the typically observed cationic. Additionally, the potential for gold-containing compounds to be active as heterogeneous catalysts makes these compounds of great interest.

This fascinating chemistry is made possible for these heavy, late 5d transition metals due to relativistic effects. The 6s orbitals are significantly contracted resulting in unusually high (for a metal) electron affinities. In fact, the electron affinity for Pt is 2.13 eV and for Au is 2.30 eV, both of which are greater than many main group elements including sulfur (2.08 eV). When surrounded by more electropositive elements, Pt and Au will readily become negatively charged (i.e., for Pt2− and Au), leading to exceptional crystal chemistry. Yet the complexity of anionic transition metal chemistry systems makes it virtually impossible to deduce the structure-composition relationship empirically. Pairing experimental studies with computational models is a useful practice to rationalize the nature of chemical bonding, leading to a refined understanding of anionic transition metal chemistry

Research in the Brgoch group focuses on employing a variety of methods to explore the crystal chemistry of these compounds. A majority of the synthesis is carried out using high-temperature sealed tube reactions while characterization consists of powder and single crystal X-ray diffraction.

 

 


The electron affinity of gold is larger than many main group elements even sulfur, leading to complex crystal structures with intriguing properties. The Brgoch group synthesizes and characterizes novel anionic transition metal compounds as well as examines the bonding and physical properties using advanced computation.

Developing Persistent Luminescent Nanophosphors via Band-gap Engineering for Multiplexing in Biological Assays

Persistent luminescence in inorganic phosphors is an optical phenomenon that provides a pathway for visible or infrared photon emission to occur for several seconds to hours after photoexcitation. The emission lifetimes of these compounds are orders of magnitude longer than the spin-forbidden transitions in phos-phorescent or metal-chelate molecules. This makes them ideal for “glow-in-the-dark” applications like safety signs, emergency displays, luminescent paints, and, more recently, as optical reporters in biological applications. Unfortunately, only a few compounds like alkaline earth aluminates possess such long lifetimes, and most of these decompose in aque-ous environments limiting biological application. The Brgoch group develops new, water-stable persistent luminescent phosphors by applying band-gap engineering to exploit the interaction between the luminescence centers and trap states for biological application.

The compounds prepared by students in the Brgoch group are used in collaboration with Richard Willson's group in Chemical Engineering in their invention of a phosphor-based immuno-chromatographic lateral flow assay (LFA) as a robust point-of-care diagnostic test. The use of phosphors effectively eliminates the need for expensive and cumbersome optical hardware that are typically required for a sensitive readout with conventional fluorescent molecules. The current research project focuses on developing persistent nanophosphors that emit at different wavelengths to allow the concurrent detection of multiple analytes, called multiplexing.



The Brgoch in collaboration with Richard Willson's group (UH Chem. Eng.) are developing a lateral flow assay (LFA) that uses a green nanophosphor as a reporter that when bound to an analyte can be captured by antibodies indicating a positive result. This technology will be expanded to include two nanophosphor reporters in the same LFA format with different optical properties allowing the concurrent detection of analytes “A” and “B” on a single test line, called multiplexing.