1. J. Lietz and J. Matheja, Naturwissenschaften, No. 21, 503–504 (1964).
2. A. I. Lapshin, V. S. Lysakov, and A. I. Serebrennikov, Zh. Prikl. Spektrosk.,11, 928–931 (1969).
3. J. Zimmerman, J. Phys. C: Solid State Phys.,4, 3265–3276 (1971).
4. W. Hohenau, Phys. Stat. Sol. (a),88, 267–276 (1985).
5. S. L. Votyakov, V. Ya. Krokhalev, V. K. Purtov, and A. A. Krasnobaev, Luminescent Analysis of the Structural Imperfection of Quartz [in Russian], Ekaterinburg (1993).