Session D2: Uponversion Physics

Upconversion White, Blue and Red Emission from Yb$^{3+}$/Er$^{3+}$/Tm$^{3+}$: Y$_{2}$SiO$_{5}$ nanocrystalline powders

The generation of white light through up conversion under the excitation of infrared laser radiation may play an important role due to its poetntial application in the lighting and display applications. Bright white up converted emission has been observed in sol-gel derived Yb$^{3+}$/Er$^{3+}$/Tm$^{3+}$ : Y$_{2}$SiO$_{5}$ nano-crystalline powders when excited with the 950 nm emission of a laser diode. The International Commission on Illumination (CIE ) chromaticity coordinates (x, y) for YET1, YET2, and YET3 nano-powders in X$_{2}$-Y$_{2}$SiO$_{5}$ crystalline form were found to be (0.334, 0.332), (0.283, 0.292), (0.353, 0.345) for white, blue and red emission under 950nm laser diode excitation with the power of 1.5W, respectively. Interestingly, the color coordinates observed change with the doping concentration of Er$^{3+}$; hence the UC emission color can be adjusted by changing the doping concentration of Er$^{3+}$.   

Broad white light emission from sol-gel derived $\alpha $-Y$_{2}$Si$_{2}$O$_{7}$ Nanoparticles activated with Yb$^{3+}$ and Er$^{3+}$ ions

We have observed white up conversion emission in sol-gel derived $\alpha $-Y$_{2}$Si$_{2}$O$_{7}$ nano powders activated with ytterbium and erbium ions when excited with the 950 nm emission of a laser diode. The emission intensities of each Er$^{3+\, }$transition decreased when the pumping power was increased from 1.7 to 2.5W with the observation of the bright wide band even at atmospheric pressure condition. When the sample was under very low pressure at 0.03 mbar and the pumping power was set from 0.9 to 2.5 Watt, the white emission brightness increased.   

Albert Bartlett and Implications of Exponential Growth

Albert A. Bartlett, late Professor Emeritus of Physics at the University of Colorado, spent the latter half of his life alerting both the community of physicists and the wider society to implications of unchecked exponential growth. Among the areas he addressed were population growth, sustainability and consumption of non-renewable resources. He placed particular emphasis on the concept of the doubling time in an exponential process, showing, for example, that the amount of a resource consumed in a doubling interval exceeds or is approximately equal to the total consumed in all of history prior to the start of that interval. We present here some examples contained in a typical Bartlett lecture or paper with the hope that, with his passing in 2013, a new generation of physicists will continue this educational effort.   

White wide-band emission from Yb$^{3+}$:Y$_{2}$Si$_{2}$O$_{7}$ nanoparticles under IR excitation

The spectral properties of Yb$^{3+}$~ions have attracted considerable attention and offered the possibility of obtaining an infrared emission and an up-converted emission. The emission properties of various host media activated with Yb$^{3+}$, have been recently studied even in nanoscale form, due to their potential photonic application. Ytterbium (Yb$^{3+})$ doped Y$_{2}$Si$_{2}$O$_{7}$ powders with average particle size 40 were successfully synthesized using the sol-gel technique. At the pressure of 0.01 mbar a wide white light band appeared. The International Commission on Illumination (CIE) coordinates (c) using an illuminance meter for nano-particles at a distance of 5cm. The CIE coordinates were found to be (0.465, 0.377) for white emission under 950~nm excitation.   

Investigations of Er and Yb Doped Y$_{2}$O$_{3}$ Nano-powders

The purpose of this research is to investigate the Er and Yb doped Y$_{2}$O$_{3}$ nano-powders, focusing on how the Er and/or Yb concentration affects absorption and infrared to visible upper-conversion luminescence from the materials. Another focus is to study how the infrared excitation power affects red and green upper-conversion luminescence. The absorption spectra are first investigated from 300 nm to 2000 nm for our five samples with various Er and Yb concentrations to determine relevant energy levels and where the strong absorptions are. Their absorption spectra show that all of them have strong absorption around 980 nm. Then the 980nm infrared to the visible upper-conversion luminescence spectra are measured and studied from 400 to 800 nm. All of our samples of different Er and Yb concentrations show strong red and/or green upper-conversion luminescence, the dependence of which on the infrared laser power is examined. Possible upper-conversion mechanisms are proposed from the results of the luminescence's power dependence. Our results show that the Er and Yb co-doped Y2O3 nano-powders can be very efficient materials for infrared to visible lighting and other important optical applications. We would like to thank BATi for providing the samples. First author also likes to acknowledge Wheaton's WRP for the support.