UV-excited Photoluminescence Research Articles

Novel epoxy-bPBD-BisMSB composite plastic scintillator for alpha, beta and gamma radiation detection

A composite plastic scintillator is prepared by uniform dispersion of organic fluorophores 2-(4-Biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (b-PBD) and 1,4-bis(2-methylstyryl) benzene (Bis-MSB) in epoxy resin followed by curing at room temperature. The developed scintillator is strong blue emitter (425 nm), confirmed by 365 nm UV excited Photo luminescence and beta particle (90Sr-90Y) excited Radio-luminescence characterizations. The developed scintillator is highly transparent (~ 70%) to emitted light wavelength. Moreover, the scintillator’s blue emission is appropriate for photomultiplier tube (PMT) based scintillation measurement due to its maximum peak spectral response in blue region. Alpha, beta and gamma radiation detection were performed on PMT coupled scintillators of sizes Ø50 mm × 1 mm, Ø50 mm × 5 mm and Ø50 mm × 25 mm respectively. Pulse height spectra were recorded using 1 k Multichannel analyser (MCA) using various reference radiation sources. All scintillators demonstrated promising response to the respective radiations. Absolute detection efficiency of alpha scintillator is obtained as 32% (241Am), 86% of that of standard plastic scintillator EJ-212. Beta endpoint energy and gamma Compton edges showed linear variation w.r.t. corresponding channel numbers. Detection efficiency of beta and gamma scintillator is found to be 35.7% (90Sr-90Y) and 6.7% (136Cs) respectively. The developed scintillator has potential to be used for radioactivity contamination & gamma dose rate measurement applications.

Photoluminescence properties of the material based on SiO2–Y2O3:Eu3+,Tb3+ under different in situ temperature prepared by the sol-gel process

The codoped SiO2–Y2O3:Tb3+,Eu3+ (xTb: 1.0 mol%; xEu: 0.1; 0.2; 0.5; 0.7 and 1.0 mol%) nanomaterials were prepared at room temperature by sol-gel process and heat treated at 900 and 1000 °C during 4 h, under air atmosphere. The materials were characterized by X-ray powder diffraction (XRD) and UV excited photoluminescence. The material exhibits Y2O3 cubic, one peak positioned around 26° assigned to the cristobalite SiO2 phase and amorphous SiO2 phases due to the Y2O3 and SiO2 presences. The emission bands observed in the emission spectra under excitation at 301 are assigned to the Tb3+ and Eu3+ ions, with clear evidence of energy transfer from Tb3+ to Eu3+. The line assigned to the 5D0→7F2 transition (Eu3+) increase the intensity as a function of Eu3+ concentration. The sensibility under controlled temperature variation was investigate. The Eu3+: 0.5 mol% doped material (annealed @900 °C) exhibited higher thermic sensitivity (with maximum relative sensitivity 0.294% K−1 in 303 K). Under excitation at 395 nm, the red color emission increases the intensity due the thermal treatment. Furthermore, CIE parameters and the color correlated temperature (CCT) are discussed in order to characterize the greenish color emission. Based on the results, these luminescence materials may be potential candidates for optical thermometry diodes, solid-state lighting and nano in vivo biological system.

Near UV excited multi-color photoluminescence in RE3+ (RE=Tb, Sm, Dy and Eu) doped Ca2Pb3(PO4)3Cl phosphors

The Ca2Pb3(PO4)3Cl: RE3+ (RE = Tb, Sm, Dy and Eu) phosphor materials were prepared by wet chemical method. The synthesized phosphors were analyzed by using XRD, SEM and photoluminescence (PL) characterization techniques. The excitation spectrum of the Ca2Pb3(PO4)3Cl:Tb3+ phosphor consists of several bands in the 300–400 nm region by monitoring emission at 545 nm, which are assigned due to electronic transitions from 7F6 to the upper levels of Tb3+ ion. The Ca2Pb3(PO4)3Cl:Tb3+ phosphor emits efficient narrow green emission at 545 nm due to 5D4 → 7F5 transition upon 371 nm excitation. The PL excitation spectrum of the Ca2Pb3(PO4)3Cl:Sm3+ phosphor exhibits narrow bands in the near ultraviolet (NUV) region due to Sm3+ ion. The Ca2Pb3(PO4)3Cl: Sm3+ phosphor shows orange red emission centered at 598 nm, which is attributed to the 4G5/2 → 6H7/2 transition of Sm3+ ion. The concentration quenching has been studied in both the cases and the critical distance was calculated as 38.5 Å. The blue (482 nm) and yellow (576 nm) emissions are obtained in the Ca2Pb3(PO4)3Cl:Dy3+ phosphor under 352 nm and 455 nm excitations, which are attributed to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy3+ ion, respectively. However, the Ca2Pb3(PO4)3Cl:Eu3+ phosphor emits strong orangish red emission centered at 594 nm, which is attributed to the 5D0 → 7F1 transition of Eu3+ ion on excitation with 396 nm. The CIE diagram shows green and orange red photoluminescence for the Ca2Pb3(PO4)3Cl:Tb3+ and Ca2Pb3(PO4)3Cl:Sm3+ phosphors, respectively whereas the bluish-yellow and orangish red photoluminescence for the Ca2Pb3(PO4)3Cl:Dy3+ and Ca2Pb3(PO4)3Cl:Eu3+ phosphors, respectively. The CIE coordinates indicate that the present phosphors have high color purity. These phosphors may act as good candidates for phosphor converted LEDs for solid state lighting technology.

Lanthanide-doped lanthanum hafnate nanoparticles as multicolor phosphors for warm white lighting and scintillators

Designing luminescent materials especially nanomaterials with multifunctional applications is highly challenging and demanding. In this work, we explored pyrochlore La2Hf2O7 nanoparticles (NPs) singly and triply codoped with Eu3+, Tb3+ and Dy3+. Under both ultraviolet and X-ray irradiations, the La2Hf2O7 NPs singly doped with Eu3+, Tb3+ and Dy3+ displayed red, green and yellowish-blue emission, respectively. The concentration quenching study revealed a non-radiative energy transfer in Eu3+ doped La2Hf2O7 NPs, which takes place via dipole-quadrupole mechanism. On the other hand, a dipole-dipole interaction prevails in Tb3+ and Dy3+ doped La2Hf2O7 NPs. Lifetime spectroscopy reveals the stabilization of Eu3+ and Dy3+ ions at La3+ site at low doping concentration whereas a fraction of them migrates to Hf4+ site at high doping concentration. For the La2Hf2O7:Tb3+ NPs, Tb3+ ions are localized at Hf4+ site at all doping concentrations. Furthermore, when triply codoped with Eu3+, Tb3+ and Dy3+ ions, the La2Hf2O7 NPs display beautiful warm white light as a new strategy for color tunability through doping percentage. To sum, our complete spectrum of studies on the structure, UV excited photoluminescence, concentration quenching, and local site spectroscopy of the La2Hf2O7:Ln3+ NPs suggests that they are potential candidates as single-component multicolor-emitting phosphors for lighting and scintillating applications.

Room temperature synthesis, concentration quenching study and defect formation in β-Ag2MoO4:Dy3+- photoluminescence and positron annihilation spectroscopy

Designing new materials for solid state lighting and understanding the various intricacies involved for designing them such as defects, energy transfer and concentration quenching is very important. Such materials will be highly beneficial in optoelectronics, energy and health industry. In this work, an effort has been taken in that direction by exploring room temperature synthesized Dy3+ doped β-Ag2MoO4 using simple co-precipitation method under neutral conditions. Pure β-Ag2MoO4 showed blue – green emission upon shining with UV light. On doping Dy3+an efficient host-dopant energy transfer takes place. The concentration quenching study revealed non-radiative energy transfer in Dy3+ doped β-Ag2MoO4 takes place via Dexter mechanism of exchange interaction. Additionally, on doping Dy3+ ions in the β-Ag2MoO4 a multicolour emission could be observed due to presence of blue, yellow and red bands induced by host sensitized energy transfer. Positron lifetime studies show that the Dy3+ doping creates cation vacancies. Positron lifetimes and asymmetry ratios in PL emission show that Dy3+stabilizes at Ag+ sites. Photoluminescence Lifetime Spectroscopy revealed non-homogenous distribution of Dy3+ ions and its surroundings differ in terms of their vicinity with respect to defects created due to aliovalent doping. Such complete spectrum of work on concentration quenching study, UV excited photoluminescence, defect spectroscopy, local structure of dopant ion and excited state lifetime indicate that the developed phosphor may potentially be used for solid state phosphor for LED application. Future work will be seeing how the material properties change in going to nanodomain and to make it excitable using f-f band (351 nm). The only demerit of this phosphor is the poor absorption in this region.

Zinc Oxide Nanostructures Doped with Transition Metals: Fabrication and Properties

ZnO nanostructured films doped with Co and Ni deposited by hydrothermal method on silicon substrates covered with undoped ZnO sublayer were studied. SEM images of the films demonstrated them to consist of densely packed vertical nanopillars. Doping ZnO films with Ni or Co at concentrations up to [Formula: see text][Formula: see text]cm[Formula: see text] quenches their UV-excited photoluminescence. The doping also leads to the slight ferromagnetic behavior of ZnO.

Photoluminescence of single-phased white light emission materials based on simultaneous Tb3+, Eu3+ and Dy3+ doping in CaWO4 matrix

The triply-doped xTb3+/xEu3+/xDy3+ CaWO4 (x: 0.5, 1.0, 2.0, 3.0, 4.0 and 5.0 mol%) nanomaterials were prepared at room temperature by a coprecipitation method. The luminescence materials were characterized by X-ray powder diffraction (XPD), thermal analysis (TG), infrared absorption spectroscopy (FTIR) and UV excited photoluminescence. The prepared powder phosphors are single-phase scheelite structure with porous morphology and particle sizes around 11 nm. The materials display white color from cool to the warm white, under UV excitation, as a result of the intraconfigurational 4f transitions from trivalent rare earth ions. The non-radiative energy transfer processes from the O→W and O→Eu LMCT as well as the 4f8→4f75d1 states to the intraconfigurational 4f excited levels of rare earth ions and simultaneous emissions from the 4F9/2 (Dy3+)→5D4 (Tb3+)→5D1,5D0 (Eu3+) emitter levels are reported. Furthermore, CIE parameters and the color correlated temperature (CCT) are discussed in order to characterize the color emission. Based on the results, these luminescence materials may be potential candidates for white light emitting diodes and solid-state lighting.

Relationships between textural and photoluminescence spectral features of carbonado (natural polycrystalline diamond) and implications for its origin

Field Emission SEM (FESEM) textural observations, crystal size distribution (CSD) analyses, UV-excited luminescence imaging, and photoluminescence (PL) microspectroscopy excited by 488 nm laser were conducted on two texturally contrasting samples of carbonado, a kind of natural polycrystalline diamond from the Central African Republic (CAR). The investigated carbonado samples A and B show extremely different textures: sample A is made up of faceted crystals accompanied by abundant, small rectangular pores, whereas sample B has a granular texture with coarser crystals and scarce, large pores. Diamond crystals smaller than 2–3 µm are enriched in sample A but depleted in sample B. These textural features indicate that sample B diamonds were annealed under thermodynamically stable P–T conditions. The pore characteristics indicate that fluid permeability was higher for sample A than sample B. Photoluminescence (PL) spectra indicate that samples A and B correspond to Group A and B carbonados in the classification of Kagi et al. (1994), respectively, so that sample A reveals emissions from the H3 center without any N–V0 derived emission at 575 nm, whereas sample B shows emissions from the 3H center and the N–V0 defect. In addition, UV-excited luminescence images and photoluminescence spectra for sample B indicate that the rims of diamond crystals within several microns of a pore show luminescence features similar to those of Group AB carbonados (Kagi et al., 1994), indicating that this Group AB material was formed from Group B by irradiation from pore-filling, radioactive-element-bearing materials at a low temperature. The extent of the low-temperature irradiation is considered to depend on fluid permeability, and the Group A material was strongly irradiated due to its permeable texture whereas the Group B material was not significantly irradiated due to its less permeable granular texture. These results indicate that Group B carbonados have retained their original PL spectral features produced under high pressures and temperatures at mantle depths.

Structural evaluations and temperature dependent photoluminescence characterizations of Eu(3+)-activated SrZrO3 hollow spheres for luminescence thermometry applications.

This research is focused on the temperature sensing ability of perovskite SrZrO3:Eu3+ hollow spheres synthesized via the sol-gel method followed by heating. The Rietveld refinement indicated that the precursors annealed at 1100 °C were crystallized to form orthorhombic SrZrO3. SrZrO3 particles exhibited non-agglomerated hollow spherical morphology with an average particle size of 300 nm. The UV-excited photoluminescence spectrum of SrZrO3:Eu3+ consisted of two regions. One region was associated with SrZrO3 trap emission, and the other one was related to the emission of Eu3+ ions. The intensity ratio of the emission of Eu3+ ions to the host emission (FIR) and the emission lifetime of Eu3+ ions were measured in the temperature range of 300–550 K. The sensitivity obtained via the lifetime method was 7.3× lower than that measured via the FIR. Within the optimum temperature range of 300–460 K, the as-estimated sensor sensitivity was increased from 0.0013 to 0.028 K−1. With a further increase in temperatures, the sensitivity started to decline. A maximum relative sensitivity was estimated to be 2.22%K−1 at 460 K. The resolutions in both methods were below 1K in the above temperature range. The results indicated the suitability of SrZrO3:Eu3+ for the distinct high temperature sensing applications.

Carrier Multiplication in a Single Semiconductor Nanocrystal.

To confirm the existence of the carrier multiplication (CM) effect and estimate its generation efficiency of multiple excitons in semiconductor nanocrystals (NCs), it is imperative to completely exclude the false contribution of charged excitons from the measured CM signal. Here we place single CdSe NCs above an aluminum film and successfully resolve their UV-excited photoluminescence (PL) time trajectories where the true and false CM signals are contained in the blinking "on" and "off" levels, respectively. By analyzing the PL dynamics of the on-level photons, an average CM efficiency of ∼20.2% can be reliably estimated when the UV photon energy is ∼2.46 times the NC energy gap.

Luminescence investigation of R3+-doped alkaline earth tungstates prepared by a soft chemistry method

Highly luminescent rare earth (R3+) doped alkaline-earth tungstates MWO4:R3+ (M2+: Ca, Sr and Ba, R3+: Eu, Tb, Gd) were prepared with a room temperature coprecipitation method. The phosphors were characterized by X-ray powder diffraction (XPD), thermal analysis (TG), infrared absorption spectroscopy (FTIR) and UV excited photoluminescence. The as-prepared MWO4:R3+ particles belong to the tetragonal scheelite phase, and are well crystallized and are of the average size of 16–48nm. The excitation and emission spectra of the materials were recorded at 300 and 77K temperatures. The luminescent materials exhibit intense red (Eu3+) and green (Tb3+) colors under UV excitation. The excitation spectra of the Eu3+ doped materials show broad bands arising from the ligand-to-metal charge transfer transitions (O2−→WVI and O2−→Eu3+) as well as narrow bands from 4f–4f intraconfigurational transitions of Eu3+. 4f–4f emission data of the Eu3+ and Tb3+ in the MWO4 host matrices as well as the values of emission quantum efficiencies of the 5D0 level and the 4f–4f experimental intensity parameters of Eu3+ ion are presented and discussed.

Host Sensitized Luminescence and Time-Resolved Spectroscopy of YVO4: Ho3+ Nanocrystals

Rare earth doped phosphors have attracted much interest because of their high chemical durability and wide range of attractive applications. In this work, Ho3+ doped tetragonal YVO4 nanocrystals have been synthesized via a facile co-precipitation method. The phosphor was characterized by various methods including X-ray diffraction, photoluminescence, cathodoluminescence, time-resolved spectroscopy measurements. The frequency upconversion emission in the synthesized phosphor has been investigated under 800nm laser excitation. UV-excited photoluminescence (PL) and cathodoluminescence (CL) measurements were performed at room temperature (300K). A broad band which arises at ∼ 370-600nm is attributed to the relaxation of VO43− groups from conduction band to valence band. Under UV-excitation, the presence of a sharp band at 550nm due to the intra-4f transitions of the trivalent holmium ions suggests energy transfer from YVO4 host to RE ions. Luminescence measurements show that this material is suitable for field emission displays (FED) and fluorescent lamps. Also the conversion of UV radiation as well as IR radiation into the visible region suggests the application of this material for photon harvesting in solar cells.

Enhancement of UV Excited Photoluminescence by Fabry-Perot Microcavity

A light-emitting microcavity with the structure of dielectric mirror/phosphor coating/dielectric mirror for the enhancement of PL efficiency excited under UV light was designed and fabricated. The fluorescence emission of Lumogen S0795 coating within microcavity structure is significantly enhanced compared with the coating on bare substrate. The measurement results indicate the possibility of developing front illuminated CCD based on optical resonant cavity for UV-visible imaging with higher sensitivity.

Zn2TiO4:Eu3+ nanophosphor: Self explosive route and its near UV excited photoluminescence properties for WLEDs

A simple and low-cost solution combustion method was used to prepare Eu3+ (1–11mol%) doped Zn2TiO4 nanophosphors at 500°C using zinc nitrates as precursors and oxalyl di-hydrazide (ODH) as fuel. The final product was calcined at 1100°C for 3h and then characterized by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–visible absorption (UV–Vis). The PXRD patterns of the sample calcined at 1100°C show pure cubic phase. The crystallite size was estimated using Scherrer’s method and found to be in the range 20–25nm and the same was confirmed by TEM studies. Effects of Eu3+ (1–11mol%) cations on the luminescence properties of Zn2TiO4 nanoparticles were studied. The samples exhibit intense red emission upon 395nm near ultra violet (NUV) excitation. The characteristic emission peaks recorded at ∼578, 592, 613 and 654nm may be attributed to the 4f–4f intra shell transitions (5D0→7Fj=0,1,2,3) of Eu3+ cations. The CIE chromaticity co-ordinates and CCT were calculated from emission spectra and the values (x, y) were very close to NTSC standard values for red emission and CCT was close to Plankian locus. Therefore, the present phosphor may be highly useful for display applications.

Mg2SiO4:Tb3+ nanophosphor: Auto ignition route and near UV excited photoluminescence properties for WLEDs

For the first time nanoparticles of Tb3+ doped (1–11mol%) Mg2SiO4 have been prepared using low temperature (350°C) solution combustion technique with magnesium nitrate as precursor and oxalyl di-hydrazide (ODH) as fuel. The Powder X-ray diffraction (PXRD) patterns of the sample revealed orthorhombic structure with α-phase. The average crystallite size using Scherer’s formula, W–H plot and Size–strain plot is found to be 28nm and the same is confirmed by Transmission electron microscopy (TEM) studies. Scanning electron microscopy (SEM) pictures show a porous structure and the crystallites were agglomerated. The effect of Tb3+ cations on luminescence characteristics of Mg2SiO4 is studied and the results are discussed in detail. The phosphors exhibit bright green emission upon near ultra violet (NUV) 377nm excitation. The characteristic photoluminescence emission peaks at 417, 436, 458nm in blue region due to 5D3→7FJ (J=5, 4, 3) of Tb3+ ions and the emission peaks at 486, 541, 584 and 621nm in green region corresponds to 5D4→7FJ (J=6, 5, 4, 3) transitions of Tb3+ ions owing to f–f transitions of Tb3+ cations in the given host lattice and are due to dipole–quadropole interactions. The CIE chromaticity co-ordinates are calculated from emission spectra and falls in green region. Therefore the present phosphor is highly useful for mercury free solid state lighting (SSL) and also for display applications.

De-excitation process in BaMgAl10O17:Eu phosphor evaluated from vacuum–UV-excited photoluminescence spectroscopy and X-ray absorption fine structure

Luminescence properties based on the valence variation of Eu ions in BaMgAl10O17:Eu (BAM) is investigated using the conversion electron yield- and fluorescence yield-X-ray absorption fine structure, and temperature dependence of PL spectroscopy to clarify the de-excitation process in BAM under UV and vacuum–UV (VUV) excitation. The baking temperature dependence of the fraction of Eu2+ ions shows three thresholds at about 600, 1000, and 1200 °C. Even though the fraction of Eu2+ in the 1200-°C-baked sample decreases to almost zero, a blue luminescence from Eu2+ still remains under VUV excitation and its intensity increases with increasing temperature. The internal quantum efficiency (iQE) of a raw sample under VUV excitation is more than 0.84. This value decreases with increasing baking temperature because of the deep trap formation accompanied with the valence change of Eu ions from divalent to trivalent. The iQE of the 1200-°C-baked sample remains 0.10, which suggests a long diffusion length of excitons in the BAM crystal after VUV excitation.

Photoluminescent Properties of Sb‐Doped Phosphate Glass

The authors report on the UV‐excited photoluminescence measured in Sb2O3–ZnO–P2O5 glass. Pre‐heat treatment performed before melting effectively prevented the discoloration caused by precipitation of Sb nanoparticles. Although both Sb3+ and Sn2+ belong to the ns2‐type emission center, the Sb3+‐doped 60ZnO–40P2O5 glass showed an emission with a weaker intensity and a broader band than Sn2+‐doped 60ZnO–40P2O5 glass. The emission decay of 1.0SbO3/2–60ZnO–40P2O5 glass was about 2.5 μs, which was shorter than that of 1.0SnO–60ZnO–40P2O5 glass. The obtained results suggest that the emission properties of ns2‐type emission centers depend on several factors, such as element of emission center, chemical composition, and preparation scheme, which are easily and widely tuned in random amorphous materials.

Photo-luminescence properties of Cu and Ag doped Li2B4O7 single crystals at low temperatures

UV excited photo luminescence from Li2B4O7:Cu and Li2B4O7:Cu, Ag single crystals has been investigated in the temperature range from 77K to 300K. An excitation band having a doublet structure at 240nm and 262nm was observed for the emission at 370nm that corresponds to 1A1g→1Eg and 1A1g→1T2g crystal field components of the 3d10→3d94s1 transition of Cu+. The relative intensity of these components and their temperature dependence provide a measure of the off-center displacement of the Cu+ ground state in the crystal lattice site. The co-doped Ag plays a role of a sensitizer when doped with Cu and increases the overall emission as the emission between Ag states lies in the excitation region of Cu states. The 370nm emission in both the crystals slightly decreases with temperature; however a sudden increase in the intensity around 264K was observed.

Strong broad green UV-excited photoluminescence in rare earth (RE=Ce, Eu, Dy, Er, Yb) doped barium zirconate

Abstract The wet synthesis hydrothermal method at 100 °C was used to elaborate barium zirconate (BaZrO3) unpurified with 0.5 mol% of different rare earth ions (RE = Yb, Er, Dy, Eu, Ce). Morphological, structural and UV-photoluminescence properties depend on the substituted rare earth ionic radii. While the crystalline structure of RE doped BaZrO3 remains as a cubic perovskite for all substituted RE ions, its band gap changes between 4.65 and 4.93 eV. Under 267 nm excitation the intrinsic green photoluminescence of the as synthesized BaZrO3: RE samples is considerably improved by the substitution on RE ions. For 1000 °C annealed samples, under 267 nm, the photoluminescence is dominated by the intrinsic BZO emission. It is interesting to notice that Dy3+, Er3+ and Yb3+ doped samples present whitish emissions that might be useful for white light generation under 267 nm excitation. CIE color coordinates are reported for all samples.

Rare Earth Doped SnO<SUB>2</SUB> Nanoscaled Powders and Coatings: Enhanced Photoluminescence in Water and Waveguiding Properties

Luminescent Eu3+ and Er3+ doped SnO2 powders have been prepared by Sn4+ hydrolysis followed by a controlled growth reaction using a particle's surface modifier in order to avoid particles aggregation. The powders so obtained doped with up to 2 mol% rare earth ions are fully redispersable in water at pH > 8 and present the cassiterite structure. Particles size range from 3 to 10 nm as determined by Photon Correlation Spectroscopy. Rare earth ions were found to be essentially incorporated into the cassiterite structure, substituting for Sn4+, for doping concentration smaller than 0.05 mol%. For higher concentration they are also located at the particles surface. The presence of Eu3+ ions at the surface of the particles hinder their growth and has therefore allowed the preparation of new materials consisting of water redispersable powders coated with Eu(3+)-beta diketonate complexes. Enhanced UV excited photoluminescence was observed in water. SnO2 single layers with thickness up to 200 nm and multilayer coatings were spin coated on borosilicate glass substrates from the colloidal suspensions. Waveguiding properties were evaluated by the prism coupling technique. For a 0.3 microm planar waveguide single propagating mode was observed with attenuation coefficient of 3.5 dB/cm at 632.8 nm.