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Ce3+-doped aluminate garnets are the main phosphors used in solid-state lighting based on blue light emitting diodes (LEDs). Recently, different compositional modifications of garnet hosts have been shown to significantly redshift the yellow-green Ce3+ emission in the garnets. We investigate the high temperature quenching of these phosphors to determine any limitations towards red emission in Ce3+-doped garnets.

The luminescence of Ce3+ in scandate perovskite hosts is investigated in this report. In general, the energy position of the Ce3+ excitation and emission bands are at lower energy versus comparable Al3+ perovskites, which is primarily attributed to a larger Ce3+ 5d1 centroid shift. The efficiency of Ce3+ luminescence is low at room temperature (

We report on the characterization of sol-gel derived lithium niobate via trivalent chromium probe ions, a study that is motivated by recent reports on the synthesis of high quality sol-gel lithium niobate (LiNbO$_3$). In order to assess the quality of sol-gel derived LiNbO$_3$, we incorporate Cr$^{3+}$ during the hydrolysis stage of the sol-gel process. A comparison of the Cr$^{3+}$ emission and photo-excitation data on both sol-gel and melt-grown LiNbO$_3$ shows that the sol-gel derived material is highly stoichiometric.

The University of Georgia, in collaboration with GE Global Research, is investigating the relevant quenching mechanism of phosphor coatings used in white light devices based on UV LEDs in a focused eighteen month program. The final goal is the design of high-efficacy white UV-LEDs through improved and optimized phosphor coatings. At the end of the first year, we have reached a fundamental understanding of quenching processes in UV-LED phosphors and have observed severe quenching in standard devices under extreme operating conditions. Relationships are being established that describe the performance of the phosphor as a function of photon flux, temperature, and phosphor composition. These relationships will provide a road map for the design of efficient white light LEDs during the final six months of the project.

The study of phosphor materials generally focuses on systems with a high quantum efficiency. On the other hand, a thorough understanding why certain systems show very low quantum yield will certainly lead to a better understanding of phosphor materials in general. Here we present studies on cerium-doped lutetium oxide and yttrium oxide crystals that are characterized by a complete quenching of the 4f-5d luminescence. To find the origin of the quenching mechanism, as well as to understand the difference to other Ce 3+ systems with high quantum efficiencies, we have performed extensive absorption, photoexcitation, and photoconductivity studies on single crystals of these systems, prepared by the laser-heated-pedestal growth technique. It is experimentally verified that the quenching mechanism is determined by the location of the first excited level of the cerium ions with respect to the conduction band - a general result that can be applied to a broad range of materials and will allow us to characterize and engineer future phosphor materials.

Y 2 O 3 :Eu 3+ has been extensively investigated as a red phosphor for fluorescent lamps and color displays. In particular, there have recently been several studies examining the effect of impurities on the luminescence efficiency for Y 2 O 3 :Eu 3+ under UV excitation. In this work we investigate the effects of codoping Y 2 O 3 :Eu 3+ with Ca 2+ and Zr 4+ on the emission produced by cathode-ray excitation. Specifically, we have measured the relative efficiency, fluorescent lifetimes, and fluorescent spectra under cathode-ray excitation and compare these results to those previously observed under UV excitation.

In GaAs-IREDs and GaAs0.6P0.4-LEDs a photoconductive and a bolometric FIR response has been observed at low temperatures by applying different pulsed optically pumped FIR lasers. The short circuit current responsivity peaks at λ=400 μm being about 1.5 mA/W. By monitoring the rapid modulation of the FIR radiation due to mode beating of the pump laser, an upper limit of 1 ns was established to the time constant of the photoconductive signal.

In this paper new methods for generation and detection of terahertz-phonons and application of these methods for a study of dynamical properties of high-frequency acoustic phonons in a crystal at low temperature are discussed. Terahertz-phonons are generated via multiphonon absorption by use of pulsed infrared radiation. For phonon detection phonon-induced fluorescence is observed. We have investigated the anharmonic decay of acoustic phonons. The experimental results indicate that the decay of acoustic phonons in the linear part of the dispersion curves can be described by a phonon decay cascade that can be characterized by a shape function. The optical techniques allow also to study for tetrahertz-phonons elastic scattering at impurities and the behaviour at crystal surfaces. We will, finally, discuss the role of the dynamics of tetrahertz-phonons for particle detection via phonons.

A new method for generation of high-frequency phonons is reported. Phonons were generated in CaF2 crystals by multiphonon absorption of infrared radiation of a CO2 laser. The new method was applied to study transient broadband spectra of nonthermal phonons.