Tulyum katkılı florotelürit optik camların termal mikroyapısal ve spektroskopik özellikleri

Thermal, microstructural and spectroscopic properties of the fluorotelluride optical glasses

Özet

Telürit esaslı cam malzemeler, katıhal lazer malzemelerinden lazer malzemesi olarak, fiber optik yükselticilerinde ve doğrusal olmayan optik camlarda kullanılan önemli fotonik malzemelerdir. Bu nedenle, telürit camlarının spektroskopik özellikleri deneysel araştırmacıların başlıca araştırma konusu haline gelmiştir. Telürit camlarının en önemli özellikleri olarak, geniş iletim bölgesine (0.35- 5 $mu m$), en yaygın oksitli camlar arasında en düşük fonon enerjisine, yüksek kırılma indisine, düşük erime sıcaklığına, yüksek dielektrik sabitine sahip olmasıdır. Ayrıca, yakın morötesinden orta kızılaltı bölgeye kadar, geniş bir geçirgenlik bölgesine sahiptir. Bu çalışmada fotonik malzeme olarak kullanılma potansiyeli olan (1-x)$TeO_2-xPbF_2 $(x=0.10, 0.15 ve 0.25 mol) optik cam malzemelerin sentezi gerçekleştirilmiştir. Bu malzemelerin termal, mikroyapı ve spektroskopik özellikleri incelenmiştir. Cam geçiş, kristallenme ve erime sıcaklıkları her bir kompozisyon için 10 °C/dak ısıtma hızı ile ölçülen DTA eğrileri kullanılarak belirlenmiştir. Kompozisyonun ve kristallenmenin bu camların yapısına etkisi X-ışını kırınımı, (XRD), Taramalı elektron mikroskopu, (SEM), Optik mikroskop (OM) ve Raman spektroskopisi (FT-IR Raman) kullanılarak incelenmiştir. Bu cam malzemeler, fiber optik iletişim ağlarında optik yükseltici olarak kullanılabilme potansiyelini araştırmak amacıyla, bir nadir toprak iyonu olan tulyum iyonu ile katkılanmıştır. Katkılanan malzemelerin (yakın kızılaltı) bölgesindeki ışıma özelliklerine tulyum iyonu konsantrasyonu etkisi lazer spektroskopisi kullanılarak incelenmiştir. 0.2 mol $Tm^{3+}$ katkılı cam malzemenin $(0.9TeO_2-0.1PbF_2)$ en yüksek ışınım kuvantum verimine sahip olması nedeniyle 1470 nm dalga boyunda fiber optik yükseltici olarak kullanılma potansiyeline sahip olduğu görülmektedir.

Abstract

Tellurite based glasses with doped rare-earth ions have attracted for the structural study and from the technological and academic point of view. Recently, considerable effort has been devoted to dielectric materials and design for optical fibers, waveguide devices and optical fiber amplifiers to improve the telecommunication sysytems. In that case, many researches have been focused on to the producing new photonic devices which have low-loss optical waveguides. $Er^{3+}$ and $Tm^{3+}$-doped tellurite photonic materials are potential candidate material for the applications in fiber-optic amplifier and fiber laser devices. Therefore, developing more stable tellurite based materials are important for applications as a technological devices. In this research, transparent tellurite glasses were prepared by using reagent $TeO_2$, and $PbF_2$. The batch materials (7 g) were well mixed in a platinum crucible and melted at 800oC for 60 min in the electrically heated furnace in air atmosphere. The glass melts were than removed from the furnace at 800oC and air-quenched by pressing between two rectangular graphite slabs at room temperature. The density of each glass sample was measured by using Archimede’s principle with distilled water as the immersion liquid (Kabalci vd. 2004). The measured density was about 6.3 g/cm3 for the glass sample. A Rigaku Thermoflex Differantial Thermal analyzer equipped with a PTC-10A temperature control unit was used in order to determine the thermal parameters. The samples of about 20 mg were heated it heating at heating rate of 10oC/min in a platinum crucible and using the same amount of $Al_2O_3$ as the reference material in the temperature range between 20 and 600oC. The $T_g$ temperature is selected as mid-point between the onset and the minimum temperature. The $T_c$ and $T_g$ temperatures were measured at the onset crystallization, and the $T_p$ temperature was measured at the peak of crystallization. The microstructural characterization of the as-cast and annealed glass samples were carried out using X-ray diffraction (XRD), and scanning electron microscopy (SEM), optical microscope and Raman spectrophotometer techniques. The x-ray diffraction investigations were carried out in a $Philips^{TM}$ Model PW3710 using $CuK_{alpha}$ radiation at 40 kV and 40 mV settings in the $2theta$ range from 10 to 90o. The crystallized phases were identified by comparing the peak positions and intensities with those in the JCPDS (Joint Committee on Power Diffraction Standards) data files. Scanning electron microscope (SEM) investigations were conducted in a $JEOL^{TM}$ Model JSM-T330 operated at 25 kV, and JEOL JSM 5410 scanning microscope, linked with a Zmax 30 Boron-up light element energy dispersive spectrometer (EDS) detector. For the SEM investigations, optical mount specimens were prepared using standard metallographic techniques followed by chemical etching in a HF solution (5%) for a minute. The etched optical samples were coated with golden. The Nikon Eclipse L150 Optical Microscope (OM) were used for microscopic observations and to obtain optical micrographs of the surfaces. The magnification levels (combined with eye-piece magnification) are, 50X, 100X, and 200X. Its magnification can be further enhanced by taking a digital image and zooming it with any image software. The Raman spectra were measured with a digilab FTS 7000 spectrophotometer in the spectral range 0-1000 $cm^{-1}$. The glass samples were excited with a Nd:YAG laser at 1064 nm with power of about 500 mW. The digital intensity data were recorded at intervals $cm^{-1}$, with 64 scans, and at resolution 8 $cm^{-1}$with a Ge detector cooled to liquid nitrogen temperature. In fluorescence measurements, samples were excited with a 25-mW continuous-wave diode laser at 785 nm. After passing through a 0.5-m Czerny-Turner type monochromator, the fluorescence signal was detected with a PbS detector and amplified in two stages by using a preamplifier and a lock-in amplifier. We also have investigated the variation of the luminescence strengths as a function of $Tm^{3+}$ ion concentration in a new type of $Tm^{3+}$ doped tellurite glass. $Tm^{3+}$ doped glasses have two emission bands that peak around 1470 nm and 1800 nm in the near infrared.