Effect of MoO3, MnO2 or mixed dopants on the spectral properties and crystallization behavior of sodium phosphate glasses containing either MgO or MgF2

Glasses from the two basic systems (Na2O-P2O5-MgO) and (Na2O-P2O5-MgF2) doped with either MoO3 or MnO2 or both of them were obtained by melting-annealing method. Characterization of both the optical and FTIR spectra for the prepared glasses were carried out together with deriving the optical band gaps and refractive indices. DTA and thermal expansion properties were investigated to reach suitable nucleation and crystallization temperatures to convert the glasses to their corresponding glass-ceramic derivatives. X-ray diffraction investigations of the glasses were primarily done to confirm their amorphous nature and then to identify the formed crystalline phases formed upon controlled thermal heat treatment with two step regime within the glass-ceramic derivatives. Optical spectra of the studied glasses reveal distinct UV absorption bands due to contaminated trace iron impurities together with the appearance of characteristic absorption bands due to molybdenum or manganese ions or both in the mixed dopants samples. FTIR spectral data indicate the appearance of vibrational peaks of phosphate groups with the interference of MgO4, MgF2 or PO3F groups. The dopants cause minor effects on the FTIR spectra. DTA and thermal expansion data support the voluminous crystallization behavior and indicating the different roles of MgO than MgF2 as reflected on the identified crystalline phases. In MgO containing glass-ceramics, the identified crystalline phase is sodium magnesium phosphate of the formula (Na3Mg2P2O16) while with MgF2-glass, two crystalline phases are identified: sodium magnesium pyrophosphate (Na2MgP2O7) beside sodium magnesium fluoride crystalline phase (NaMgF3). This refers to the compactness of the network of glasses with MgO due to its refractoriness and possibility of the formation of structural MgO4 groups. On the other hand, MgF2, is assumed to act in glass during crystallization as efficient nucleating agent as CaF2 and it is assumed to lower the melting temperature and ease of crystallization.