Comparison between crystal field effects on the fluorescence spectra of crystalline SmP5O14 and vitreous (Sm2O3)(0.248)(P2O5)(0.752)

To investigate how the local symmetry of the Sm3+ ion affects the fluoresce nce of a samarium metaphosphate glass of composition (Sm2O3)(0.248)(P2O5)(0 .752), the temperature and pressure dependences of its laser induced fluore scence spectrum are compared with those of a samarium pentaphosphate crysta l (SmP5O14). Findings include: (i) The crystal field splitting of the energ y levels responsible for fluorescence in SmP5O14 at room temperature is con sistent with the local symmetry of oxygen atoms of the phosphate cage aroun d the Sm3+ ions being quite close to cubic - in accord with crystal structu re. At 12 K there is a systematic disappearance of the shortest wavelength lines of each fluorescence band attributable to a decreasing population of higher crystal field levels, which are occupied at ambient temperature. (ii ) The (Sm2O3)(0.248)(P2O5)(0.752) g lass fluorescence spectrum forms five b ands, which can be related to that of the crystal but with inhomogeneous li ne broadening; the short wavelength edges sharpen at low temperatures, also attributable to a decreasing population of higher crystal field levels at lower temperatures. (iii) The shifts (d lambda/d rho) in the wavelengths of the fluorescence peaks of the SmP5O14 crystal induced by pressure up to 50 kbar in a diamond anvil cell are small but measurable at room temperature, being about +0.03 nm kbar(-1) (+0.3 Angstrom kbar(-1)). Application of pre ssures up to 50 kbar to the (Sm2O3)(0.248)(P2O5)(0.752) glass did not alter the positions of the bands within the error in the fluorescence wavelength measurements. Neither the SmP5O14 crystal nor the metaphosphate glass show ed any indication of undergoing a phase transition up to the highest pressu re reached. A low frequency Raman mode has been observed, which softens wit h reducing temperature, indicating softening of the associated optical mode and suggesting that, like other RP5O14 crystals, SmP5O14 undergoes a ferro elastic phase transition. (C) 1999 Kluwer Academic Publishers.