Independently this class of phosphors initially has been proposed and investigated in Technical University of St-Petersburg. We have begun to develop new phosphors based on silicon nitride and related systems more than 10 years ago. Thus we have a sum of knowledge in crystal chemistry and technology of sialons doped by lanthanides and of its optical-emission properties, technical characteristics of phosphors, the durability to UV, alfa-,beta-, gamma-particles irradiation including. The preliminary results can be summarized as follows.
The criteria of selection of promising composition matrix are based on analysis of changes in chemical bond caused by dissolving of different elements in the domain of homogeneity of alpha-sialons[2,3]. The original approach of so called "coordination balance" together with more classic "balance of charges" permits to find the compositions with optimal short order[4 ]. The more local ionicity in activator surrounding, the better the conditions for luminescence.
We have investigated the reaction of silicon powder with gaseous mixtures possessing variable nitridising-oxydising potentials. A mechanism of oxygen segregation is revealed and thus the contradictions with thermodynamics of Si-O-N system became comprehensible [5].
Silicon nitride doped with Tb(III) shows the characteristic luminescence with narrow main emission lines centered at 545 nm. The f-d absorption band of Tb(III) in silicon nitride overlaps too well with the emission line 254 nm from mercury low pressure discharge. All the green-emitting lamp phosphors do not overlap with this line and must be sensitized with Ce and Gd. The silicon nitride does not need such expensive doping. The doping of silicon nitride with Eu(II) is preferred as an activator for the yellow-green broad emission. The spectral position of the Eu (II) excitation band overlaps well all short and longwave ultraviolet mercury lines. Hence the application of nitride phosphor improves the efficacy (about 5%) of the high-pressure mercury vapour lamps. During 18000 hours of service no degradation was been observed.