Classification of stark structure in spectra of Nd-doped glasses

The absorption spectra of Nd3+ ions in more than 120 binary compositions of silicate, phosphate, germanate and borate glasses containing M2O (M = Li, Na, K, Rb, Cs), MO (M = Be, Mg, Ca, Sr, Ba) and M2O3 (M = Al, La) oxides as modifiers were investigated at 80 K. The study has revealed a number of cases when the absorption spectra of different glass-former-based glasses exhibit a striking similarity of spectral contours. Based on this result we introduce a concept of 'spectrum type' and classify all investigated spectra into types, the spectra of different glasses with similar contours being combined within one type. The spectrum variations with equimolar change of a modifier type and with alteration of a modifier (alkaline oxide) content were analyzed in terms of this classification. The analysis led to an inference about 'the chemical composition' of the second coordination sphere of Nd3+ ions for a number of types of neodymium centres. Recommendations for modelling of RE-doped glasses is proposed.