The Absorption Edge of the High Index Glass of Ultra-High Purity

Study on the Color of High Index Glass, Part 5

Abstract

Optical absorption of ultra-pure glasses containing two kinds of oxides giving high index of refraction has been measured in the near ultraviolet region. The relations among the color, ultraviolet absorption edge, refractive index, Abbe's number and the wavelength of intrinsic absorption of high index glasses of ultra-high purity has been discussed.
The results obtained are as follows:
1) Logarithm of absorbance of ultra-pure glasses decreased linearly as the wavenumber decreased at the rate d(logα)/d(1/λ)≅1×10^-3cm.
2) The glasses having the absorption edge at an wavelength longer than 370nm appeared yellow or brownish yellow.
3) The wavelength of absorption edge was longer for the glass of high index of refraction, low value of Abbe's number and long wavelength of intrinsic absorption.
4) The preparation of colorless glass having the index n_D larger than 1.95, Abbe's number ν_D less than 22 or intrinsic wavelength longer than 170nm is supposed to be very difficult for the system containing PbO, TiO₂ and Nb₂O₅.