A series of unconventional twisted intramolecular charge-transfer (TICT) chromophores was designed and synthesized. These chromophores exhibit ultra-large first hyperpolarizabilities. The structural characteristic that promotes this unusual nonlinear optical response is a sterochemically enforced reduction of the D- π-A conjugation that enforces zwitterionic behavior in the ground state and provides a low-energy, large-oscillator strength intramolecular excitation feature. The consequence is that molecules with relatively small numbers of π-electrons exhibit responses far larger than those of traditional planar π-conjugated chromophores. At 1907 nm, non-resonant νβ values as high as -466,000 × 10-48 esu are observed.

We report on the gain study in high-quality thick GaN layers using the Variable Stripe Length (VSL) technique. The layers were grown by Migration Enhanced Metal Organic Chemical Vapor Deposition (MEMOCVDTM). The amplification of light was investigated for the propagation directions along the layer surface (perpendicular to the c-axis of the crystal) and perpendicular to the layer (along the c-axis) for the layers with thicknesses up to 11 νm. By fitting the experimental stripe length dependence of the edge luminescence with one-dimensional description of light amplification in medium with positive gain, peak gain coefficients of up to 7300 cm-1 were estimated in GaN at the excitation power density of 2 MW/cm2. We discuss limitations of the VSL technique due to the assumption of one-dimensional light propagation and strong influence of gain saturation in a high-gain medium. The contribution of new gain modes after saturation of the highest-gain modes was observed. The optical gains in GaN samples with different carrier lifetimes (obtained using time-resolved photoluminescence and light-induced transient grating techniques) were compared.

Continuous-wave and time resolved photoluminescence measurements on europium doped gallium nitride in the form of a powder are presented. The powder is obtained from reacting NH3 and a melt of gallium and europium with bismuth as a wetting agent. Photoluminescence from continuous wave excitation above the GaN bandgap reveals that an optimal concentration of about 1 at.% of Eu gives the most intense emission at 621 nm. Above gap time resolved photoluminescence reveals that energy transfer between the host material (GaN) and the rare earth ions occurs at a faster rate than previously reported for MBE grown GaN:Eu. Applications of the powder are directed towards CMOS compatible light emitters that are spun on silicon. A high temperature anneal of the powder shows no change in the CW photoluminescence spectrum of the powder, confirming CMOS compatibility.

Using the site-selective technique of combined excitation emission spectroscopy, we have studied a variety of Er doped silicon oxide layers with and without silicon nanocrystals. This technique allows clear distinction of cluster defect sites that are created during thermal annealing and become dominant for higher Er ion concentration and are suppressed by the presence of nanocrystals. In several samples, we were able to observe fluorescence line narrowing under resonant excitation allowing defect-selective excitation.

Pulsed Electron Beam Deposition (PEBD) and Pulsed Laser Deposition (PLD) were used to grow Gallium Oxide (Ga2O3) thin films on double sided polished sapphire substrates. At 850°C substrate temperature, smooth single crystal β-Ga2O3 films were obtained, which were confirmed with measurements by AFM of RMS surface roughness of about 1 nm. When characterized under electron beam excitation, the films exhibited different responses. For example: Europium doped films emitted intense red emission from 5D0 to 7Fj transitions while exhibiting weak broad emission from 300 to 500 nm. In contrast, Erbium doped films emitted strong emission from 300 to 500 nm peaked at 360 nm that was attributed to defects in the host matrix. Green emission from the Erbium transitions was observed at 528 and 550 nm. Films with different rare earth compositions varying from 0.1 % to 0.4 % were also prepared.

High quality natural waveguides were formed with the deposited Ga2O3 films on the lower refractive index substrate sapphire. This was confirmed by measuring the refractive index by prism coupling and sharp coupling spectra.

Silicon rich silicon oxide films were fabricated by electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD). The films were doped in situ using an organometallic precursor. Optical measurements show that the refractive indices of the films are determined by the silane to oxygen flow rate ratio used during the depositions. The erbium content as measured by elastic recoil detection (ERD) is also strongly dependent on the oxygen flow rate, with more erbium being incorporated in the more highly oxygenated films. The erbium content was also found to vary inversely with plasma power, which did not have a significant effect on the silicon to oxygen ratio. This allows the erbium and excess silicon levels of the films to be controlled independently.

Er3+, Nd3+ and Tm3+ doped Si/ZrO2 thin films have been prepared by rf co-sputtering. The films are 5 inches long and divided into 50 sections or positions, labeled from P1 to P50. The target configuration is such that the main target is ZrO2 (181.46 cm2), the rare earth (RE) oxide pellet (1.43 cm2) is placed on the main target below the middle of section of the film and the Si chip (6.67 cm2 or 6.00 cm2) is placed on the main target below one end of the film (P40 to P50). The films were annealed to 700°C. The Er3+4I13/2→4I15/2 emission was detected but no 4I13/2→4I15/2 emission was detected. The 4I13/2→4I15/2 emission shows a narrow peak at 1527 nm (FWHM = 6.5 nm for P20) with two weaker side bands from 1430 nm to 1500 nm and from 1550 nm to 1600 nm. The Nd3+4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2 emissions were detected being the 4F3/2→4I11/2 peaked at 1065 nm (FWHM = 39.5 nm for P30) the strongest. The 4F3/2→4I9/2 emission is relatively weak, less than one-fourth the peak intensity of the 4F3/2→4I1/2 emission but is broad (FWHM = 92 nm for P30). No Er3+4I13/2→4I15/2 emission or Nd3+4F3/2 emissions were detected for the Si rich ends of the respective films, being the emission stronger from the Si poor end of the film towards the middle of the film. The maximum Er3+4I13/2→4I15/2 emission is for P20 and the maximum peak intensity for the Nd3+4F3/2→4I11/2 emission is for P30. The excitation wavelength dependence behavior for the Nd3+4F3/2→4I11/2 emission is that typical of energy transfer from the Si nanoparticles to the emitting Nd3+ ions. The excitation wavelength behavior for the Er3+4I13/2→4I13/2 emission reflects a mix of energy transfer from the Si nanoparticles and strong absorption for excitation wavelengths of 488.0 nm and 514.5 nm. The Tm3+ doped Si/ZrO2 thin film does not exhibit infrared (IR) PL from the 3H4 emission or the 3F4→3H6 emission. The intense band from 500 nm to 800 nm observed for all of the RE doped Si/ZrO2 films, due to defects in ZrO2, barely permits the detection of the Tm3+3H4→3H6 emission which is best observed for P35.

We report on the fabrication and luminescent properties of rare earth-doped gallium nitride (GaN) phosphor powders. Single phase GaN and GaN:RE3+ powders were prepared by using a novel chemical route.

In this work a new method for the synthesis of high purity, single phase doped GaN powders is reported. (Ga1-xREx)N powders are obtained by dissolving metal nitrates (Ga(NO3)3, (RE(NO3)3) in deionized water and an organic fuel (hydrazine) in order to form a gallium/RE amorphous/nanocrystalline powder. The RE-oxide powders are then reacted with heated ammonia at different temperatures and processing times producing GaN:RE phosphors. X-ray diffraction analysis showed that single phase GaN powders are formed. Preliminary results show (Ga0.95Eu0.05)N powders are luminescent, with the main emission occurring at 611 nm which is due to the 5Do→7F2 transitions in Eu3+. High-purity GaN powders are obtained according to Xray photoelectron spectroscopy (XPS) chemical analysis. Low-temperature cathodoluminescence and photoluminescence measurements indicate that the emission at λ=611 nm is originated from energy transfer from the host to the rare earth ion and to a direct excitation to the Eu3+ electronic levels.

This method can be used to obtain red-luminescence GaN:Eu3+ and other rare earth (e.g. Er, Tb, Tm)-doped GaN powders to produce green and blue luminescence as well.

It is one of the curious twists of technology that transitions which are parity forbidden in the free ions of rare earths should have become of immense importance in solids used in fluorescent lighting, cathode ray tubes and optical amplifiers. It is not an unreasonable expectation that having achieved such success with excitation from photons and accelerated electrons that junction electroluminescence should also be important. Since Ennen demonstrated good low temperature electroluminescence in silicon in the early 80's, a formidable amount of work has been done to try to understand the excitation and quenching mechanisms in common semiconductor hosts such as silicon and gallium arsenide. Although some remarkable experimental results have been obtained for erbium in nanostructures, insulators and wide bandgap materials the performance in bulk silicon and silicon germanium is disappointing. More importantly we still have not achieved a comprehensive, detailed understanding of the processes of non-radiative competition to the rare earth emission. In this paper the key steps that have been made over the last twenty years towards our present day knowledge of erbium luminescence in semiconducting hosts are reviewed and an assessment made of what remains to be done.

The emission properties of Eu doped GaN thin films prepared by interrupted growth epitaxy (IGE) were investigated through excitation-wavelength dependent and time-resolved photoluminescence (PL) studies. Under above-gap excitation (333-363 nm) large differences were observed in the Eu3+ PL intensity and spectral features as a function of Ga shutter cycling time. The overall strongest red Eu3+ PL intensity was obtained from a sample grown with a Gashutter cycling time of 20 minutes. The main Eu3+ emission line originating from 5D0→ 7F2 transition was composed of two peaks located at 620 nm and 622 nm, which varied in relative intensity depending on the growth conditions. The room-temperature emission lifetimes of the samples were non-exponential and varied from ∼50 νs to ∼200 νs (1/e lifetimes). Under resonant excitation at 471 nm (7F0→5D2) all samples exhibited nearly identical PL spectra independent of Ga shutter cycling time. Moreover, the Eu3+ PL intensities and lifetimes varied significantly less compared to above-gap excitation. The excitation wavelengths dependent PL results indicate the existence of different Eu3+ centers in GaN: Eu, which can be controlled by the Ga shutter cycling time.

The GaN:RE phosphor development plays a major role in the GaN:RE AC thick dielectric electroluminescent (TDEL) device optimization. In this paper we report on EL devices fabricated using Eu-doped GaN red phosphors films grown by interrupted growth epitaxy (IGE). IGE consists of a sequence of ON/OFF cycles of the Ga and Eu beams, while the N2 plasma is kept constant during the entire growth time. IGE growth of GaN:Eu resulted in significant enhancement in the Eu emission intensity based primarily at 620.5nm. The increase in the material crystallinity observed with the IGE phosphors appears to be the dominant cause of the emission enhancement. Thick dielectric EL devices fabricated on glass substrates using IGE-grown GaN:Eu have resulted in luminance of ∼1000 cd/m2.

Amorphous aluminum oxide (Al2O3) thin films codoped with Tm3+ and Er3+ have been prepared by pulsed laser deposition. A broad emission band with a full-width half maximum (FWHM) up to 230 nm was observed in Tm-Er codoped film. The spectrum shows two peaks located at 1540 nm corresponding to Er3+ emission and 1640 nm due to Tm3+ emission. The luminescence intensity dependence on the annealing temperature was investigated. It is shown that the annealing temperature and energy transfer between Tm3+ and Er3+ ions play an important role in the definition of the luminescent response.

Er3+/Pr3+ co-doped soda-lime glass thin films have been fabricated using RF magnetron sputtering method and their structural and optical properties have been studied. Deposition rate, crystallinity, and composition of glass thin films were investigated by scanning electron microscopy, transmission electron microscopy, and electron probe micro area analysis. Refractive index, birefringence and binding characteristics have been investigated using a prism coupler and x-ray photoelectron spectroscopy. Er3+/Pr3+ co-doped soda lime glass thin films were prepared by changing substrate temperature (room temp.∼550 ), RF power (90W∼150W), and Ar/O2 gas flow ratio at processing pressure of 4mTorr. Glass thin films could be obtained at the optimized processing condition at 350, RF power (130W), and gas flow (Ar:O2=40:0) with maximum deposition rate of 1.6νm/h. Refractive index increased from 1.5614 to 1.5838 and birefringence increased from 0.000154 to 0.000552 as the content of Pr3+ increased. Binding energy of Pr3d increased as the content of Pr3+ increased.

We have synthesized amorphous- SiCxOy (a-SiCxOy) (x, y: 0 - 1.65) materials via thermal chemical vapor deposition (TCVD) at 800°C using a single source oligomer, 2,4,6-trimethyl-2,4,6-trisila-heptane (C7H22Si3) and ultra-high purity oxygen (O2). The Er-doped SiCxOy materials exhibited a strong room-temperature photoluminescence (PL) at ∼1540 nm at an excitation wavelength of 496.5 nm. Furthermore, the infrared PL intensity was found to be highly dependent on the compositions of carbon and oxygen, with the maximum PL intensity obtained for an Er-doped SiC0.50O1.00 thin film, which exhibited a ∼20-times enhancement in the PL intensity as opposed to the Er-doped SiO2 control samples.

The PL intensity decreased significantly as the matrix evolves into either the SiC-like or SiO2-like material. Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) were used to characterize the local elemental electronic environment in a-SiCxOy. Our work indicates a strong correlation between the emission of Er luminescence and the formation of Si-C-O bonding in materials.

A novel deposition process has been developed for manufacturing of high quality rare-earth doped glass films with complex composition. This process, Laser Reactive Deposition (LRDTM), comprises photothermal laser pyrolysis using an aerosol feedstock coupled with deposition of the resulting nanoparticle product onto Si substrates with our without an underlying glass film. This paper describes this novel process as well as the structure, properties and performance of the Erdoped, multicomponent silicate glass films produced to date with this process.

Bridged polysilsesquioxanes were synthesized by modifying the Si-O-Si polymeric network to produce highly nanoporous glasses for facile and uniform doping of nanoparticles. By taking advantages of void volumes created through the molecular modification technique, we designed and synthesized hexylene- and fluoroalkylenebridged polysilsesquioxanes doped with both Er+3 ions/CdSe nanoparticles for amplifier applications. Significant enhancement in fluorescence intensity at 1540 nm has been observed from the fluoroalkylene-bridged glass. Analysis by nuclear magnetic resonance (NMR) indicates a dramatically enhanced degree of condensation and a low level of hydroxyl environment in the fluoroalkylene-bridged hosts. The presence of CdSe nanoparticles, by virtue of their low phonon energy, also appears to significantly influence the nature of the surrounding photoluminescence environment of Er+3 ions in those organically modified hosts, resulting in the increased photoluminescence intensity.

In this work the high resolution optical spectroscopy is used in order to determine the positions of the Stark split 4I15/2, 4I11/2 and 4I9/2 energy levels of Er3+ in GaN and GaN:Mg. Photoluminescence and photoluminescence excitation spectra were measured at energies corresponding to the 4I15/2→4I9/2 and 4I15/2→4I11/2 absorption transitions. Low Er implant doses were applied to reduce the number of possible defects. In undoped GaN only a single Er-center was observed and no influence of Mg doping on the energy level splittings of this center in GaN:Mg was found. Numerical analysis based on point charge model was used to calculate parameters of the local crystal field (CF) acting on Er3+ ions. The splittings of the 4I9/2 and 4I11/2 energy levels were calculated in weak CF approach and good agreement with experimental results was obtained. The calculations confirmed that the symmetry of the erbium center in hexagonal GaN is C3v.

Temperature dependence of time-resolved photoluminescence (PL) properties for rare-earth ions (REIs: Eu, Tb, and Er) implanted AlxGa1-xN (x=0∼1) is investigated. Thermal quenching for RE-related PL becomes small when increasing the Al contents. The PL decay time of REIs used in the present work becomes shorter when increasing the temperature and/or PL peak energy. The temperature dependence of PL intensity and the decay time are analysed by assuming phonon assisted energy-back-transfer model, in which the energy in REIs escape to trap levels. From the results, the improvement of PL properties can be well explained by the model, in which the activation energy for energy-back-transfer process is increased as increasing the Al contents.

A new photoluminescence (PL) band in the energy range of 700 meV to 950 meV associated with hafnium implanted in silicon is reported. A shift in the position of photoluminescence peaks observed on the samples implanted with two different isotopes of Hf confirms the Hfrelated origin of the observed photoluminescence band. Activation of the Hf-optical centers requires a 1000°C anneal step. The intensity of the PL lines depends on the cooling conditions. The spectrum consists of five peaks in the rapidly quenched sample as opposed to twenty one in the slowly cooled sample. Temperature dependent PL measurements and hydrostatic pressure measurements were performed to identify their nature.

Site-selective combined excitation emission spectroscopy studies have been performed on Eu-doped GaN and numerous sites have been identified. Relative numbers and broadening of these peaks has been investigated for different growth conditions and for increasing AL content of the AlxGa1-xN alloy.