Disorder effects in Nd³⁺-doped strontium hexa-aluminate laser crystals

Abstract

The high resolution and polarized absorption spectroscopic data of Nd 3+ -doped, Mg 2+ -compensated strontium hexa-aluminate Sr 1−x Nd y La x−y Mg x Al 12−x O 19 (ASL: Nd) crystals in an extended compositional range (0.01 x 0.5) are presented. This crystal offers for the Nd 3+ ions a unique crystallographic site (2d) with 12 O 2− coordination and ideal D 3h symmetry. The optical spectra in all this compositional range contain contributions from two families of structural centres, C 1 and C 2 (with two components C 2 and C 2 ), whose spectral features are mainly dependent on the composition parameter x. The presence of these centres is attributed to the cationic disorder. It is inferred that while the centres C 1 and C 2 are connected with the presence or absence of trivalent ions in the nearest (2d) coordination sphere normally occupied by Sr 2+ , the two components C 2 and C 2 are associated to the existence or lack of Mg 2+ ions in the nearest sphere of Al 3+ tetrahedral (Al 3+ tetr ) sites. This structural disorder leads to crystal-field perturbations by electric charge difference, although for C 1 centres the perturbation by ionic size differences is also evident. The polarized spectroscopy indicates departures from the selection rules for D 3h symmetry for C 1 centres, whereas both polarized spectra and crystal-field analysis confirm the near-D 3h symmetry for C 2 centres. The composition dependence of the spectra indicates that the distribution of the La 3+ and Nd 3+ ions at the (2d) sites is random, while that of the Mg 2+ in the Al 3+ tetr sites is correlated with the former. The connection of this structural model with the EPR data and with earlier models is discussed.

Spectroscopic studies of Yb3+-doped rare earth orthosilicate crystals

“…The observation of satellites in the absorption spectra of lanthanide-doped compounds is a fairly common phenomenon which has been extensively studied in materials such as garnets or rare earth sesquioxides [15], in Nd 3+ activated YVO 4 and YLiF 4 [16] and in Nd:Ca 4 M(BO 3 ) 3 O, M = Gd, Y [17]. They have been interpreted in terms of (i) perturbed sites associated with lattice defects [17], (ii) modification of the crystal field at the lanthanide site due to the formation of ion pairs [15] and (iii) occurrence of magnetic exchange coupling between lanthanide ions in pairs [16]. In Yb 3+ -doped compounds, ion pairing was also observed and evidenced mainly through cooperative absorption or luminescence effects [18][19][20].…”

Long Persistent Luminescent HDPE Composites with Strontium Aluminate and Their Phosphorescence, Thermal, Mechanical, and Rheological Characteristics

“…In recent years, different phases of rare-earth-doped (Pr 3+ , Ce 3+ , Sm 2+ , Nd 3+ , etc.) aluminates were developed, and their emission wavelength depends upon the crystalline structure of the alkaline earth metal aluminate phase [ 13 , 14 , 15 , 16 , 17 , 18 ]. Among these phosphors, SrAl 2 O 4 : Eu, Dy and Sr 4 Al 14 O 25 : Eu, Dy have displayed a robust potential for phosphorescence applications and are available commercially [ 19 , 20 ].…”