Abstraction: The optical soaking up of Ti: Al2O3 individual crystal has been measured at room temperature, in the wavelength part between 200 nanometers to 800 nanometers. The chief soaking up extremums at 491 nanometers and 562 nanometer, the weak infrared soaking up set with a extremum at 650 nanometers and the strong UV soaking up set below 300 nanometers were observed. The refractile index is discussed utilizing Fresnel ‘s equation. In peculiar, the Sellmeier equation was determined in the seeable part by agencies on non-conventional method based on the measuring of refraction by utilizing UV-visible spectrometry. The refractile indices decreased from 3.71 to 1.28 with wavelength in the scope 400 – 800 nanometer.
Keywords: Optical Absorption, Refractive Index, Ti: Al2O3, UV-visible spectrometry.
Aluminum oxide ( Al2O3 ) is a technological and industrial stuff of great involvement, both for cardinal surveies and for application, because of its hardness, good electrical insularity, utile optical belongingss, high surface country, and catalytic surface activity [ 1 ] . Aluminum oxide ( sapphire ) being an of import technological stuff is used as lasing stuff in solid province optical masers, substrate for micro-electronics ceramic, radiation dosemeter, an dielectric for the wall of atomic merger reactors and so on [ 2 ] . Pure Al2O3 is a lasting stuff with optical transmittal crossing the scope from UV to IR. Discovery of lasing action in Cr doped Al2O3 has created a footing of modern optical maser engineerings. This function has been taken over more late by Al2O3 doped Ti that is now successfully used as tunable optical maser stuff [ 3 ] . Titanium: Al2O3 ( Ti: sapphire ) is utile tunable optical maser stuff in the close infrared spectra part of 0.7 nm – 1.1 µm. Crystal of Ti: Al2O3 exhibit a wide soaking up set, located in the bluish green part of the seeable spectrum that is associated with phonon-coupled excitement of the 3d negatron of the Ti3+ ions [ 4 ] .
Optical belongingss of Ti: Al2O3 crystals have been studied [ 3-7 ] . The measuring of the optical soaking up coefficient near the cardinal soaking up border is a standard method for the probe of optically induced electronic passage in many stuffs. By and large, two types of optical passage i.e. direct and indirect occur at the soaking up border [ 8 ] . Both of these passages occur when an electromagnetic moving ridge interacts with a valency negatron and raises it across the energy spread to the conductivity set.
In this paper, a elaborate probe on the optical soaking up of Ti: Al2O3 in the seeable and UV part is presented. The room temperature coefficient of reflection and transmission informations is analyzed to identity the refractile index of the individual crystal Titanium: Al2O3. The refractile index of a stuff depended on the crystal construction [ 9 ] . Atoms which are easy polarisable, ( i.e. easy displaced ) , negatrons, give rise to a high refractile index, while those with tightly bound electron give rise to a low refractile index.
In this survey, we examined Ti: Al2O3 individual crystal doped with 0.1 wt. % Ti. The sample was obtained from RODITI International ( England ) . The sample for measuring was polished at both of the big faces to an optical quality. The optical soaking up, transmission and refractiveness spectrum was obtained utilizing a Perkin Elmer UV-3101 Personal computer UV-VIS-IR spectrophotometer in the scope 200-800 nanometer at room temperature.
Result and Discussion
The soaking up spectra of the Ti: Al2O3 individual crystal at room temperature is shown in Figure 1. The spectra exhibit two broad sets in the scope 400 – 600 nanometer, associated with the passages within different d-levels of the Ti3+ ions ( t2g & A ; agrave ; eg passage ) [ 10,11 ] . The chief soaking up is a dual structured set with overlapping extremums at 491 nanometers and 562 nanometer, due to passages from the 2T2 land province of Ti3+ to the 2E aroused province. The consequences are similar as reported by Yamaga et.al [ 6 ] . The seeable set at 491 nanometer is the crystal filed soaking up set and corresponds to intra-configurationally passage t2g & A ; agrave ; eg of the d1 constellation in the octahedral field estimate. The bluish green soaking up set of Ti: Al2O3 is due to the vibronically broadened 2T2 & A ; agrave ; 2E passage [ 4 ] . The weak infrared soaking up set with the extremum at 650 nanometers and the strong UV soaking up set below 300 nanometers are observed in sample. In the soaking up spectrum of Ti: Al2O3 is the strong charge transportation soaking up which appears below 300 nanometer. Due to the charge transportation soaking up which satisfies both spin and para choice regulations, it is strongly electric dipole allowed, with oscillator strength [ 5 ] . This strong soaking up makes the observation of construction within the set utilizing crystal of moderate dopant concentration and seasonable thickness really hard. Tippins reported in Lacovara [ 5 ] has studied the charge transportation sets of Ti ( and other passage metals ) in Al2O3, utilizing low concentrations and thin samples. Tippins ‘s spectrum of Ti: Al2O3 assigns a bulge in the UV soaking up energies are between 5.5 electron volts and 8 electron volts due to the charge transportation
Ti3+ + O2- & A ; agrave ; Ti2+ + O-
This is in good understanding with a simple theory. A diminished bulge appears about between 4.5 electron volts and 5 electron volt is attributed to the charge transportation
Fe3+ + O2 & A ; agrave ; Fe2+ + O- .
Fig. 1 Absorption spectra observed at room temperature for Ti: Al2O3 individual crystal
In the UV portion of the spectra two strong soaking up sets centered at 234 nanometers ( 5.30 electron volt ) and 216 nanometer ( 5.74 electron volt ) . This observation indicates that the two sets are of different beginnings. As a affair of fact, the alleged E-band centered at 5.30 electron volt in the soaking up spectrum of Al2O3-Ti3+ set was attributed to a edge excited of Ti3+ , whereas the 5.74 electron volt set is attributed to 2pO2 & A ; agrave ; 3dTi4+ charge transportation passages [ 9 ] .
Determination of Refractive Index
The refractile index of Ti: Al2O3 individual crystal can be calculated from the transmittal spectrum in the wavelength part of 300 – 800 nanometer utilizing the Fresnel equation [ 12 ] :
( 1 )
where R is the coefficient of reflection and N is the refractile index. The coefficient of reflection can be calculated from the transmission spectrum utilizing the undermentioned equation:
( 2 )
The transmittal spectrum of Ti: Al2O3 individual crystal was measured as shown in Figure 2. The refractile index was calculated utilizing Fresnel ‘s equation from measurement refraction by utilizing UV-visible spectrometry. The scattering dealingss were calculated utilizing Sellmeier ‘s refractile index scattering distribution [ 13 ] .
( 3 )
where N is the refractile index, is the wavelength, and A, B, C, D, and E are known Sellmeier parametric quantities. The Sellmeier expression is selected since it facilitates a more compact look for the fitting equation than would by and large be expected from a wholly empirical preparation. Besides, this expression frequently provides at least a unsmooth usher to the values of the other physical parametric quantities of the optical stuff. Two footings in the Sellmeier equation, as in Eq ( 3 ) , was used to suit the informations consisting of the ordinary and extraordinary refractile index values measured at given wavelengths.
In the mensural scope, the Sellmeier equation fitted really good with the experimental values. The fitting parametric quantities are shown in Table 1. The extrapolation to the short wavelength part showed, the Sellmeier tantrum is realistic, because the latter implied that the stuff is crystalline at wavelength shorter than that at the soaking up border, as can be observed in Figure 3. The Sellmeier equation, with dual resonance frequences ( B, D ) is accurate plenty at short wavelengths. The refractile index for the extraordinary moving ridge is much larger than that of the ordinary moving ridge, hence, Ti: Al2O3 is an optically uniaxial positive crystal.
Fig. 2 The transmission spectrum of Ti: Al2O3 individual crystal
Table 1. Table of Sellmeier coefficients from the adjustment of measured refractile indices utilizing Sellmeier equation. The corresponding curves are shown in Figure 3
Fig.3 Extraordinary and ordinary refractile indices of Ti: Al2O3, Ne and no, severally, and the deliberate curve tantrum with the Sellmeier equation. The corresponding adjustment coefficients are given in Table 1
A typical consequence of refractile index obtained by utilizing Sellmeier suiting methods is shown in Figure 3. The refractile index depends on the wavelength. That is clear the refractile index decreased with wavelength. It can be seen excessively, that the truth of the reconstructed curve is really good, which showed a really little absolute difference between the experimental and interpolated values.
The Ti: Al2O3 individual crystal exhibited double-structured soaking up extremums at 491 nanometers and 562 nanometer, the weak infrared soaking up set with a extremum at 650 nanometers and a strong UV soaking up set at 234 nanometer. The optical consequences indicated that the chief soaking up is due to stray Ti3+ ion, whereas the parasitic infrared set is due to Ti3+ – Ti4+ braces. The refractile indices of Ti: Al2O3 individual crystal as a map of the wavelength has been determined by the Fresnel equation and the scattering dealingss were calculated utilizing Sellmeier ‘s equation. The extraordinary refractile index is much larger than the ordinary one, hence Ti: Al2O3 is an optically uniaxial positive crystal.