Dongdong Jia

The time, size, viscosity, and temperature dependence of the Brownian motion of polystyrene microspheres

An upper division undergraduate laboratory module to study Brownian motion was developed using polystyrene microspheres suspended in a sample liquid cell that was isolated from its surroundings. The dependence of the Brownian motion of the microspheres on their radius, the time, the viscosity of the suspension liquid, and the temperature were measured using a CCD camera interfaced with a frame grabber and a computer. The motion of each particle was monitored for 5minutes and was found to be consistent with the Langevin formula for Brownian motion.

Two-dimensional nanotriangle and nanoring arrays on silicon wafer

Gold and tungsten were deposited on silicon wafer and/or glass substrates by using random incidence sputtering deposition and thermal vapor deposition techniques. Two-dimensional tungsten nanotriangle and gold nanoring arrays were obtained on the silicon wafer substrate and examined using scanning electron microscope and atomic force microscope analysis. The size of the equal tungsten nanotriangles is within 100 nm per side and 210 nm apart from each other. The size of gold nanorings is 220 nm diameter, 40 nm wide, 10 nm thick, and 560 nm apart from each other. No nanorings were found on the glass substrate. Mechanisms for the formation of nanoring arrays are discussed.

Preparation of Green, Yellow and Red Long Persistent Nanophosphors

Long persistent nanophosphors of ZnS:Cu (Green), ZnO:Mn (Yellow) and CaO:Eu (Red) were prepared through precipitation method. n-heptane was used as a stabilizer to control the particle growth. Green emission of Cu in ZnS was found at 506 nm, yellow emission of Mn in ZnO was found at 572 nm, and red emission of Eu in CaO is found at 616 nm. The average growth rate of CaO nanophosphor was 4.72 nm/s. Adding a stabilizer can stop the particle growth and aggregation. Smaller particle size was obtained by adding n-Heptanes at earlier time.

Long persistent light emitting diode indicators

An undergraduate laboratory was designed for undergraduate students to make long persistent light emitting diode (LED) indicators using phosphors. Blue LEDs, which emit at 465 nm, were characterized and used as an excitation source. Long persistent phosphors, SrAl2O4:Eu2+,Dy3+ (green) and CaS:Eu2+,Tm3+ (red), were used as light converters. These phosphors were coated onto the LEDs to produce an afterglow emission once the LEDs were switched off. The indication time of the indicators was extended due to the afterglow emission from phosphors. The emission spectra, afterglow emission spectra and afterglow decay curves of the LED indicators were measured by using a photodetector. These long persistent LED indicators have important applications in emergent situations when electrical power is unavailable.

Sulfide Phosphors for LED White Light Sources

Several sulfide phosphors, such as CaS:Ce3+,Na+, CaS:Eu2+,Ce3+, ZnS:Te,Mn, ZnS:Se,Te,Mn and ZnS:Ce,Li were prepared and their excitation and luminescent spectra were investigated. The possible applications in LED-Phosphors white light devices are discussed.