Yttrium Aluminum Garnet Crystals Research Articles

Microstructure and Luminescent Properties of the YAG: Ce Phosphor-Doped Glass of the P<sub>2</sub>O<sub>5</sub>-ZnO-SiO<sub>2</sub> System

Lminescent glass is widely used in building, energy saving, emergency lighting and art crafts; The energy consumption for global illumination is rising year by year, and the energy consumption has become a global problem; the research of luminescent glass is important for the developing of the energy-saving light. In this paper, the glass of the P2O5-ZnO-SiO2 system was used as matrix material, the matrix material was doped with yttrium aluminum garnet crystals containing Ce (YAG:Ce phosphors) and then were sintered for the preparation of the luminescent glass. Using X-ray diffraction and fluorescence spectrometer, the effects of the doping quantity, sintering temperature and sintering time on luminescent properties were studied. The results show that, for the P2O5-ZnO-SiO2 glass, excitation at 340 nm and 468 nm, produced emission at 544 nm; Doping quantity, sintering temperature and sintering time affect intensity of emission peak, but do not affect the position of emission peak.

Energy levels of exciton traps in yttrium aluminum garnet single crystals

Electronic defects and exciton traps were studied in yttrium aluminum garnet (YAG) single crystals by wavelength and temperature resolved thermoluminescence (TL). Measurements were carried out from room temperature to 400 °C on a number of rare earth (RE) doped and undoped YAG crystals, and the trap parameters were determined. Although the TL emission spectrum is characteristic of the RE ion, the main trap levels are found to be characteristic of the undoped host crystal. Nevertheless, the thermal activation energies of the traps are slightly modified by doping. The trap kinetics are found to be of the first order in both undoped and Ce doped YAG single crystals indicating the absence of retrapping, which suggests that the traps and recombination centers exhibit a close spatial correlation. The effect of annealing on TL response suggests that some of the major traps are associated with oxygen vacancies.

Preparation and optical properties of sol–gel derived thick YAG:Ce3+ phosphor film

A sol–gel process for the preparation of thick YAG:Ce3+ films has been developed. YAG:Ce3+ phosphor films with a typical yttrium aluminum garnet (YAG) photoluminescence (PL) profile were prepared successfully. Single phase YAG films with a maximum thickness of 2μm were prepared in the present work. The refractive index of the YAG films prepared (∼1.85 @ 633nm and ∼1.80 @ 1540nm) was very close to that of YAG single crystal. It was confirmed that the PL efficiency of the prepared films was strongly related to the degree of YAG phase formation in the samples and the rate of YAG phase evolution strongly depended on the film thickness. To achieve high YAG:Ce3+ PL efficiency, a minimum 1.2μm of thickness is necessary. It was also found that the optical quality of the YAG films decreased following the deposition and thermal annealing processes, probably as a result of the growth of YAG crystals inside. As an example of a compromise between high PL efficiency and good optical quality, prism coupling was achieved on a 30-layer planar waveguide sample annealed at 1000°C for 30min. It was proved that this sample could support multiple waveguide modes at visible wavelengths and its propagation loss at 1540nm was estimated at 4.2dB/cm. The temperature quenching effect in the films of the present work was also measured, being the same as that of commercial YAG:Ce3+ phosphors with relatively high Ce concentration. The present technology is intended for YAG:Ce3+ phosphor films that may be applied on white LED and it may also be of benefit to any areas where YAG films may be of interest.

Optical detection of a single rare-earth ion in a crystal.

Rare-earth-doped laser materials show strong prospects for quantum information storage and processing, as well as for biological imaging, due to their high-Q 4f↔4f optical transitions. However, the inability to optically detect single rare-earth dopants has prevented these materials from reaching their full potential. Here we detect a single photostable Pr3+ ion in yttrium aluminium garnet nanocrystals with high contrast photon antibunching by using optical upconversion of the excited state population of the 4f↔4f optical transition into ultraviolet fluorescence. We also demonstrate on-demand creation of Pr3+ ions in a bulk yttrium aluminium garnet crystal by patterned ion implantation. Finally, we show generation of local nanophotonic structures and cell death due to photochemical effects caused by upconverted ultraviolet fluorescence of praseodymium-doped yttrium aluminium garnet in the surrounding environment. Our study demonstrates versatile use of rare-earth atomic-size ultraviolet emitters for nanoengineering and biotechnological applications.

The effect of TiO2 and ZrO2 addition on the crystallization of Ce3+ doped yttrium aluminum garnet from glasses in the system Y2O3/Al2O3/SiO2/AlF3

The crystallization of yttrium aluminum garnet (YAG) doped with Ce3+ from alkali free glasses in the system Y2O3/Al2O3/SiO2/AlF3 has been investigated with and without the addition of ZrO2 and/or TiO2 as nucleation agents. X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA) were used to characterize the crystallization process. Fluorescence microscopy and fluorescence spectroscopy were used to investigate optical properties. Thermal annealing of the glass was carried out at temperatures in the range from 1100 to 1400°C. In all samples studied, crystallization at temperatures ≥1300°C lead to the formation of YAG as the main crystalline phase. If the glass contained TiO2, the crystallization of YAG occurred at lower temperatures; here, already at 1150°C, YAG was the main crystalline phase. After annealing at 1300°C, the only crystalline phase formed was YAG. The fluorescence intensity showed a maximum at a wavelength of 532nm and was largest in the sample solely doped with 5mol% TiO2. This proves that Ce3+ was incorporated into the YAG crystals.

Strong visible and near infrared luminescence in undoped YAG single crystals

Strong luminescence peaks were observed at 700 and 800 nm in undoped yttrium aluminum garnet (YAG) single crystals. They were attributed to low level of iron impurities as confirmed by Glow Discharge Mass Spectrometry analysis. The 800 nm was only excited by high energy band at 270 nm; the reason behind that was discussed. Photoluminescence measurements revealed a large number of luminescence peaks in all YAG crystals regardless of the growth conditions due to native defects and low-level impurities. These luminescence centers have significant effects on the optical properties of rare-earth doped YAG crystals and their performance in laser and scintillation applications. Excitons released in the lattice may be easily captured by iron ions instead of Ce3+ ions and the scintillation output is substantially decreased. Nevertheless, Undoped YAG crystals may have the potential to be developed into efficient scintillators.

Spodumene and garnet luminescence excited by subnanosecond electron beams

Pulsed cathodoluminescence of spodumene and yttrium-aluminum garnet crystals activated by Mn2+ and Nd3+ ions, respectively, is investigated. The luminescence was excited upon crystal irradiation by electron beams with current densities of 35 and 100 A/cm2 and average electron energy of ∼ 50 keV for 0.1, 0.25, and 0.65 ns. It is demonstrated that the electron beam duration decreased to several tenth of a nanosecond does not lead to essential changes of the mechanisms of pulsed cathodoluminescence excitation and character of its spectrum, but in this case, the intensity of luminescence of the hole centers increases compared with the intracenter luminescence.

Internal photopumping of Nd3+ (2H9/2, 4F5/2) states in yttrium aluminum garnet by excitation transfer from oxygen deficiency centers and Fe3+ continuum emission

Photoexcitation of Nd3+ (2H9/2, 4F5/2) states by the broad (∼70 nm FWHM), near-infrared continuum provided by Fe3+ has been observed at 300 K in bulk yttrium aluminum garnet (YAG) crystals doped with trace concentrations (<50 ppm) of Fe, Cr, and Eu. Irradiation of YAG at 248 nm with a KrF laser, which excites the oxygen deficiency center (ODC) in YAG having peak absorption at ∼240 nm, culminates in ODC→Fe3+ excitation transfer and subsequent Fe3+ emission. This internal optical pumping mechanism for rare earth ions is unencumbered by the requirement for donor-acceptor proximity that constrains conventional Förster-Dexter excitation transfer in co-doped crystals.

Theoretical Studies of the Electron Paramagnetic Resonance and Optical Spectral Data for Vanadium(IV) Ion in Yttrium Aluminum Garnet Crystal

ABSTRACT Four spin-Hamiltonian parameters (g factors g // and g ⊥ and hyperfine structure constants A // and A ⊥) and two optical spectral band positions for vanadium(IV) (V4+) ion in the tetrahedral Al3+ site of yttrium aluminum garnet (Y3Al5O12) crystals are calculated from the (third-order) perturbation theory method (PTM) and complete diagonalization (of energy matrix) method (CDM). Both methods are based on the cluster approach. The calculated results from both methods coincide and reasonably agree with the experimental values. The defect structure of V4+ center (which is different from the corresponding structure in the host crystal) in Y3Al5O12 crystal is also obtained from the calculation.

Simple method to join YAG ceramics and crystals

Method to join samples of yttrium aluminum garnet (YAG) ceramics and crystals together includes deposition of thin SiOx layer(s) on flat polished surfaces of the samples to be joined and heating the samples with the contacting surfaces above 1700°C. There is no visible border between the crystal samples bonded. YAG single crystal solid state growth takes place on the bonded crystal–ceramics border, and crystal growth velocity is much higher when intermediate SiOx layer is used.

Intensities of hypersensitive transitions in garnet crystals doped with Er3+ ions

We examine the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er3+ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of garnets with different contents of Al3+ and Sc3+ ions (Gd2.4Er0.5Sc1.8Al3.3O12, Gd2.4Er0.5Sc1.9Al3.2O12, Gd2.4Er0.5Sc2.0Al3.1O12) is performed, as a result of which the oscillator strengths and the intensity parameters Ωt (t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca3(NbGa)5O12 crystals doped with Er3+ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity parameter Ω2 of Er3+ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the symmetry of the local environment of Er3+ ions in these crystals is C1, C2, or C2ν. We reveal that, as the concentration of Er3+ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition 4I15/2 → 2H11/2 of Er3+ ions and their intensity parameter Ω2 tend to decrease, which can be related to an increase in the relative fraction of Er3+ ions with higher symmetry of the local environment.

Power scalability and frequency agility of compact terahertz source based on frequency mixing from solid-state lasers

We investigate power scalability and frequency agility of a terahertz (THz) source by mixing two frequencies generated by solid-state lasers in a nonlinear crystal. They are made possible by introducing two solid-state laser crystals sharing the same Q switch and output coupler with the same laser beams decoupled to each other by a polarizer. Following the optimization, we have improved the THz output power nearly fivefold at 1.64 THz. By replacing one of the neodymium-doped lithium yttrium fluoride crystals with a neodymium-doped yttrium aluminum garnet crystal, we have produced 2.1 μW at 2.98 THz.

Energetic Bessel–Gauss pulses from diode-pumped solid-state lasers

We discuss the generation of Bessel–Gauss pulses directly from a diode-pumped solid-state laser. The laser resonator has a plano–concave configuration with the concave end mirror replaced with a diffractive phase element. As the active material, Nd-doped yttrium lithium fluoride (YLF) and GdVO4 crystals have been used. The pulsed operation is obtained by passively Q-switching the laser using Cr4+:yttrium aluminum garnet (YAG) crystals with different unsaturated transmission coefficients. When guiding the pulses out from the resonator through the laser crystal, 5–10 ns long pulses with energies of 40–50 μJ and peak powers on the order of 10 kW are obtained. Even 70 μJ is possible, but this is achieved at the expense of slightly deteriorated beam quality in the far field.

Growth of Nd-doped YAG powder by sol spray process

Yttrium aluminum garnet (YAG) and neodymium-doped yttrium aluminum garnet (Nd-YAG) nano-crystalline powders were successfully grown using cost effective sol spray process without the addition of any chelating agent or organic templates. Thermal decomposition behavior was studied by thermogravimetry (TG) and differential thermal analysis (DTA). Results revealed that crystallization of YAG started around 920 °C. The shrinkage/expansion behavior of synthesized powder was examined by dilatometer and revealing that sintering kinetics of these materials can be related to the evaporation of binder and formation of crystalline phases. Nano-crystallinity and garnet structure of YAG and Nd-YAG specimens were analyzed by Raman, fourier transform infra red (FTIR), and X-ray diffraction (XRD) techniques. XRD patterns were indexed using Rietveld refinement method. Smaller lattice parameter and a small change in atomic position of oxygen were found in Nd-YAG when compared with YAG structure. Scanning electron microscope (SEM) results indicated that particle size of Nd-YAG was <150 nm. The morphology of Nd-YAG nanosized powder was rounded in shape.

Grain growth and microstructural evolution of yttrium aluminum garnet nanocrystallites during calcination process

An yttrium aluminum garnet (YAG) precursor precipitate was synthesized by urea method using yttria (Y2O3) and aluminum nitrate (Al(NO3)3·9H2O) as raw materials. The fresh wet precipitate was dried by supercritical carbon dioxide (CO2) fluid and the resulting powder was calcined at temperatures from 600 to 1600 °C. Crystallization of YAG was detected at 800 °C, and completed at 900 °C. HRTEM images of the YAG product obtained above 900 °C revealed crystallographically specific oriented attachment along the [1 1 2] direction. Based on the observation of the particle morphology a possible growth mechanism of YAG nanoparticles was presented. The fast increase on the average crystallite size of YAG at temperatures from 900 to 1300 °C is attributed to the crystallographically specific oriented attachment growth process. As the growth process proceeds at higher temperatures, oriented attachment based growth becomes less important because of the increase on particle size, and the self-integration assisted by the Ostwald ripening becomes dominant.

Micro-segregations in liquid phase sintered silicon carbide ceramics

The densification behaviour of LPSSiC ceramics with different amount of secondary phases was investigated during Field Assisted Sintering (FAST). In the densified materials micro-segregations were found with dimensions of several 100 μm. Sometimes such segregations were found in gas pressure sintered materials. The investigation of the state of crystallisation by EBSD and XRD revealed that these micro-segregations are connected with the formation of large YAG (Yttrium aluminium garnet) crystals. The mobility of yttrium in the grain boundaries was investigated by measuring concentration profiles in diffusion couples. The high diffusion coefficient determined at 1850 °C (10 −6 cm/s) indicates that the observed segregations are caused by the crystallisation kinetics of the secondary phases during cooling.

Light storage protocols in Tm:YAG

We present two quantum memory protocols for solids: a stopped light approach based on spectral hole burning and a storage in an atomic frequency comb. These procedures are well adapted to the rare-earth ion doped crystals. We carefully clarify the critical steps of both. In one case, we show that the slowing-down due to hole-burning is sufficient to produce a complete mapping of field into the atomic system. On the other side, we explain the storage and retrieval mechanism of the Atomic Frequency Comb protocol. These two critical stages of the protocols are implemented experimentally in Tm 3 + -doped yttrium–aluminum–garnet crystal.

Nd3+- and Cr3+-Doped Yttrium Aluminum Garnet Ceramic Pulse Laser Using Cr4+-Doped Yttrium Aluminum Garnet Crystal Passive Q-Switch

A passively Q-switched Nd3+-and Cr3+-doped yttrium aluminum garnet (YAG) ceramic laser using Cr4+:YAG crystal as a Q-switch element is reported for the first time. Unique temporal waveforms of the output laser pulses were observed. A temporal waveform of a Q-switched laser pulse was compared with one in a free-running pulse. Laser pulses of 130–300 ns duration were generated. A maximum output laser energy of 1.1 J and an average peak power of 0.1 MW were obtained for multiple Q-switched pulses by a single shot, and a maximum output laser energy of 80 mJ was obtained for a single pulse. The evaluated maximum peak power was 0.6 MW as determined from measured pulse energy and duration. The effective saturation fluence and maximum stored energy were lower than those of Nd:YAG. However, a high peak power can be obtained using an output coupler with a low reflectivity owing to the high gain as in the case of Nd:YAG. The threshold of the Nd/Cr:YAG ceramic laser oscillator is reduced to less than 10% of that of a Nd:YAG oscillator. It was determined by calculation that the output laser energy of the Nd/Cr:YAG ceramic laser was close to 4 times that of Nd:YAG.

Thermoluminescence properties of carbon doped Y3Al5O12 (YAG) crystal

In this work, carbon doped yttrium aluminum garnet (YAG) (YAG:C) crystal was grown by the temperature gradient technique in a reducing atmosphere. The optical and thermoluminescence (TL) properties of the as-grown YAG:C crystal were investigated. Four absorption bands at 235, 255, 298, and 370 nm and a main blue emission peak at 400 nm are observed in the YAG:C crystal. The absorption coefficients of the bands at 235 and 370 nm, which are associated with the F+-center, increase sharply in YAG crystal by the introduction of carbon. As-grown YAG:C crystal shows high TL sensitivity, and three main glow peaks at 390 K (P1), 465 K (P2), 524 K (P3) and two weak glow peaks at 580 and 625 K are found. The TL dose responses of the three main glow peaks show linear-supralinear characteristic, and wide linearity dose response are found in P1 and P2 glow peaks. The temperature position and TL intensity of three main glow peaks show a strong dependence of heating rate in YAG:C crystal.

On the fabrication of all-glass optical fibers from crystals

The highly nonequilibrium conditions under which optical fibers conventionally are drawn afford considerable, yet underappreciated, opportunities to realize fibers comprised of novel materials or materials that themselves cannot be directly fabricated into fiber form using commercial scalable methods. Presented here is an in-depth analysis of the physical, compositional, and selected optical properties of silica-clad erbium-doped yttrium aluminosilicate glass optical fibers derived from undoped, 0.25, and 50 wt % Er3+-doped yttrium aluminum garnet (YAG) crystals. The YAG-derived fibers were found to be noncrystalline as evidenced by x-ray diffraction and corroborated by spectroscopic measurements. Elemental analysis across the core/clad interface strongly suggests that diffusion plays a large role in this amorphization. Despite the noncrystalline nature of the fibers, they do exhibit acceptable low losses (∼0.15–0.2 dB/m) for many applications, broad-band emissions in the near-infrared, and enhanced thermal conductivity along their length while maintaining equivalent mechanical strength with respect to conventional silica optical fibers. Further, considerably higher rare-earth doping levels are realized than can be achieved by conventional solution or vapor-phase doping schemes. A discussion of opportunities for such approaches to nontraditional fiber materials is presented.