YAG Hosts Research Articles

CO2 laser post-treatment of sol-gel-derived Y3Al5O12:Ce phosphor ceramic powders

Cerium-doped yttrium aluminum garnet (Y3Al5O12:Ce, YAG:Ce) was prepared using a sol-gel method and then fired for CO2 laser post-treatments. Phase transformations and formation of impurities were not observed in YAG:Ce after CO2 laser sintering. The shift of the diffraction peak and the appearance of another Raman peak indicate a more homogeneous distribution of Ce activators and enhanced crystallinity in laser-sintered YAG hosts. Larger spheres (100–200 μm) with tiny crystallites (<10 μm) were observed on the smoother surface in the laser-sintered YAG:Ce, unlike the irregular, porous, and layered powders in the sol-gel-derived YAG:Ce (1–100 μm). Photoluminescence (PL) measurements revealed an emission increase of 180% and a red shift of the emission peak for the laser-sintered YAG:Ce powders compared with the sol-gel-derived powders. Both have comparable thermal PL quenching behavior; however, the YAG:Ce powders with CO2 laser treatment exhibited a PL efficiency improvement of approximately 4%.

Resonant excitation cross-sections of erbium in freestanding GaN bulk crystals

Erbium doped GaN (Er:GaN) is a promising candidate as a new gain medium for high energy lasers. The excitation and emission mechanisms as well as the transition cross sections of the pump and laser wavelength are of paramount importance for understanding the performance of lasers and amplifiers made of Er:GaN materials. We report here the results of direct measurements of resonantly excited photoluminescence emission, photoluminescence excitation, and optical absorption spectroscopy in the 1.5 μm “retina-safe” spectral region performed on freestanding Er:GaN bulk crystals synthesized by hydride vapor phase epitaxy. The results established that 1514 nm and 1538 nm are the most appropriate resonant pump wavelengths for achieving gain and lasing, which differs from Er in YAG and glass hosts. The absorption coefficients (α) and absorption cross-sections (σexc) of Er in GaN in the 1.5 μm window have been directly measured, providing σexc = 1.4 × 10−20 cm2 and 2.7 × 10−20 cm2 for 1514 nm and 1538 nm pump wavelengths, respectively. These values are considerably higher than those of Er ions in glass and YAG hosts.

Luminescent properties of LuAG:Yb and YAG:Yb single crystalline films grown by Liquid Phase Epitaxy method

In this work, investigation of the spectroscopic parameters of the luminescence of Yb3+ ions in single crystalline films of Lu3Al5O12 and Y3Al5O12 garnets was performed using the synchrotron radiation excitation with the energy in the range of Yb3+ charge transitions (CT), exciton range and the onset of interband transitions of these garnets. The basic spectroscopic parameters of the Yb3+ CT luminescence in LuAG and YAG hosts were determined and summarized with taking into account the differences in the band gap structure of these garnets.

Bi3+–Pr3+ energy transfer processes and luminescent properties of LuAG:Bi,Pr and YAG:Bi,Pr single crystalline films

Absorption, cathodoluminescence, excitation spectra of photoluminescence (PL) and PL decay kinetics were studied at 300K for the double doped with Bi3+–Pr3+ and separately doped with Bi3+ and Pr3+ Lu3Al5O12 (LuAG) and Y3Al5O12 (YAG) single crystalline film (SCF) phosphors grown by the liquid phase epitaxy method. The emission bands in the UV range arising from the intrinsic radiative transitions of Bi3+ based centers, and emission bands in the visible range, related to the luminescence of excitons localized around Bi3+ based centers, were identified both in Bi–Pr and Bi-doped LuAG and YAG SCFs. The energy transfer processes from the host lattice simultaneously to Bi3+ and Pr3+ ions and from Bi3+ to Pr3+ ions were investigated. Competition between Pr3+ and Bi3+ ions in the energy transfer processes from the LuAG and YAG hosts was evidenced. The strong decrease of the intensity of Pr3+ luminescence both in LuAG:Pr and YAG:Pr SCFs phosphors, grown from Bi2O3 flux, is observed due to the quenching influence of Bi3+ flux related impurity. Due to overlap of the UV emission band of Bi3+ centers with the f–d absorption bands of Pr3+ ions in the UV range and the luminescence of excitons localized around Bi ions with the f–f absorption bands of Pr3+ ions in the visible range, an effective energy transfer from Bi3+ ions to Pr3+ ions takes place in LuAG:Bi,Pr and YAG:Bi,Pr SCFs, resulting in the appearance of slower component in the decay kinetics of the Pr3+ d–f luminescence.

Bi3+–Ce3+ energy transfer and luminescent properties of LuAG:Bi,Ce and YAG:Bi,Ce single crystalline films

The absorption, cathodoluminescence, excitation spectra of photoluminescence (PL) and PL decay kinetics were studied at 300K for the double Bi3+–Ce3+-doped and separately Bi3+- and Ce3+-doped Y3Al5O12 (YAG) and Lu3Al5O12 (LuAG) single crystalline film phosphors grown by liquid phase epitaxy method. Emission bands in the UV range arising from the intrinsic radiative transitions of Bi3+-based centers, and emission bands in the visible range related to the luminescence of excitons localized around Bi-based centers, were identified in both Bi–Ce and Bi-doped YAG and LuAG SCF. Energy transfers from the host lattice to Bi3+ and Ce3+ ions and from Bi3+ to Ce3+ ions were investigated. Competition between Bi3+ and Ce3+ ions in the energy transfer from the YAG and LuAG hosts was evidenced. A strong decrease of intensity of the Ce3+ luminescence both in YAG:Ce and LuAG:Ce SCF phosphors, grown from a Bi2O3 flux, is observed due to the quenching influence of Bi3+ flux related impurity. Due to overlap of the visible emission band of Bi3+ centers with the absorption band of Ce3+ ions peaking at around 450–460nm, an effective energy transfer from Bi3+ ions to Ce3+ ions takes place, resulting in the appearance of a slower component in the Ce3+ luminescence decay kinetics.

Thermal stability of luminous YAG: Ce bulk ceramic as a remote phosphor prepared through silica-stabilizing valence of activator in air

A prototype of YAG: Ce (Y3Al5O12) luminous bulk ceramic as a remote phosphor for white LED illumination was fabricated in air through a strategy of silica addition. With increasing the amount of silica in a specific range, the opaque sample turns to be semi-transparent. The precipitation of crystals is verified to be in pure YAG phase by X-ray diffraction (XRD). Beyond the limit of silica amount, the dominant phase of YAG crystal is found to coexist with a small amount of newly-formed Y2Si2O7, Al2O3 and the amorphous phase. The YAG crystals are with a grain size of approximately 2 μm and distribute evenly. The YAG hosts after structural modification via addition of silica result in yellow band emission of 5d → 4f transition peaked around 535 nm as excited by a blue LED, owing to the self-reduction of Ce4+ to Ce3+ even in the absence of reductive atmosphere.

Judd–Ofelt analysis of the Er3+ (4f11) absorption intensities in Er3+−doped garnets

Spectroscopic and laser properties of three different Er3+−doped garnet systems are characterized by employing the Judd–Ofelt (JO) analysis. The three garnet hosts are Y3Al5O12 (YAG), Y3Sc2Ga3O12 (YSGG), and Gd3Ga5O12 (GGG). The JO model has been applied to the room temperature absorption intensities of Er3+ (4f11) transitions to establish the so-called JO intensity parameters: Ω2, Ω4, and Ω6 in the three garnet hosts. The intensity parameters are used to determine the radiative decay rates (emission probabilities of transitions) and branching ratios of the Er3+ transitions from the excited state J manifolds to the lower-lying J′ manifolds. The predicted decay rates and branching ratios of these Er3+ transitions in YAG, YSGG, and GGG hosts are compared. From the radiative decay rates, the radiative lifetimes of the Er3+ excited states are determined in the three garnets and are also compared. We also report the spectroscopic quality factors, Ω4/Ω6, obtained for the three garnets. The quantum efficiencies of the I413/2→I415/2 Er3+ transition in YAG, YSGG, and GGG are determined to be ∼79%, 82%, and 85%, respectively.

Ion-pair upconversion pumped laser emission in Er3+ ions in YAG, YLF, SrF2, and CaF2 crystals

Ion-pair upconversion pumped laser emission at 2.7–2.9 μm between the 4I11/2 and 4I13/2 excited states of triply ionized erbium ions (Er3+) has been studied at 300 and 100 K in YLF, YAG, SrF2, and CaF2 hosts. Laser action was obtained by pumping directly into the transition’s terminal laser level. In all four hosts, the lifetime of the 4I13/2 state is longer than that of the 4I11/2 state, by factors of 5 and 80 for the first two, and factors of (5)/(2) and 2 for the SrF2 and CaF2, respectively. The absorption coefficient for the 1.533-μm pump radiation is comparable in YLF, SrF2, and CaF2, but is larger by a factor of 3 in YAG. At room temperature the threshold pump energy for YAG is larger by a factor of 10 than for CaF2, SrF2, and YLF. Interpretation of the lasing delay times at threshold pumping levels in terms of a simple analytic model gives for the upconversion coefficients: αYLF =1.2×10−17 cm3 s−1, αYAG =5.4×10−17 cm3 s−1, αSrF2 =2.9×10−15 cm3 s−1, and αCaF2 =3.2×10−15 cm3 s−1. Nonoptimized upconversion pumped laser efficiency in Er:YLF was measured at 110 K to be 17%. A peculiar upconversion pumped lasing behavior was observed in Er:YAG at low temperatures.

End-Pumped ND:BEL Laser Performance

Performance data for a cw Nd:BEL laser end pumped by two 500 mW laser diode arrays are presented and compared with the performance data for a Nd:YAG laser in a similar configuration. The phased arrays used as the pump source are cooled by a temperature-controlled heat sink to permit wavelength tunability. Although the absorption band-width for Nd:BEL is substantially broader than for Nd:YAG, the Nd:BEL was found to have a higher threshold for lasing. Both rods gave slope efficiencies of 42%. The dependence of the output power on output mirror reflectivity was measured, with Nd:BEL showing a greater sensitivity to reflectivity than Nd:YAG. The optimum reflectivities were found to be 0.98 for Nd:BEL and 0.97 for Nd:YAG. The maximum TEM00 cw power achieved for each rod at these reflectivities was 250 mW for Nd:BEL and 283 mW for Nd:YAG. The observed electrical-to-optical conversion efficiency was factored into a product of analytic component terms, and excellent agreement was found between observed and calculated efficiencies. It is concluded that under the conditions used in this work, both BEL and YAG hosts perform comparably. The conditions under which BEL might out-perform YAG as a host for diode-pumped Nd are discussed.

Stimulated emission in multiply doped Ho3+:YLF and YAG - A comparison

A comparison of threshold and slope efficiency is made for 2-μm laser action in Ho <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> -doped YLF and YAG hosts at room temperature. Spectroscopic and laser properties of these materials are also discussed.