Abstract
The optical and luminescent properties of undoped La3Ga5.5Ta0.5O14 lanthanum- gallium tantalate crystals grown in dif- ferent atmospheres of pure argon gas and argon gas with different oxygen percentages have been studied. The optical absorption α(λ) spectra that characterize integral absorption and reflection have been measured in the 250–700 nm re- gion. The spectral absorption functions have been calculated from the measured α(λ) spectra using the Kubelka–Munk formula. Luminescence has been observed in all the test specimens over a wide spectral region (375 to 650 nm) at 95 and 300 K. The luminescence spectra of the test crystals have a fine dispersed pattern represented by low-intensity discrete luminescence peaks. The 95 K luminescence peak maxima are more pronounced and shifted towards shorter wavelengths by ~16 nm (~0.1 eV) relative to the respective room temperature peaks. The crystal growth atmosphere has been demonstrated to largely affect the luminescent properties of the crystals: the higher the oxygen concentration in the growth atmosphere, the lower the luminescence intensity due to concentration quenching, the luminescence peak max- ima shifting towards longer wavelengths. The positions of discrete luminescence peaks have been shown to correlate with the main 420 and 480 nm absorption bands with the respective ~20 nm (~0.2 eV) Stokes shift for crystals grown in different atmospheres. The luminescence in lanthanum-gallium tantalate crystals is a complex process involving several luminescence mechanisms.
Conclusion
Luminescence parameters were for the first time obtained for langatate single crystals grown in different atmosp- heres. The luminescent and optical properties of lantha- num-gallium tantalate crystals were studied at 95 and 300 K for different growth atmosphere. Growth atmosphere was found to dramatically affect the luminescence intensity: with increasing oxygen con- centration in the growth atmosphere the luminescence in- tensity decreased as a result of concentration quenching.We stated that a specific feature of the luminescence centers in the test crystals is their fine dispersed pattern consisting of low-intensity discrete luminescence peaks spaced from one another by 0.03 eV on average and pre- sumably attributed to the exciton structure of the lumines- cence centers. Gauss analysis showed that with increasing oxygen concentration in the langatate growth atmosphere the lumi- nescence peak maxima of these crystals shift towards lon- ger wavelengths. The luminescence in lanthanum-gallium tantalate crystals is a complex process involving several radiation mechanisms which require a more detailed study.
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