Spectroscopic and structural properties of Nd3+ doped strontium lanthanum aluminate laser crystals

Abstract

Nd 3+ -activated strontium lanthanum aluminate Sr1−xNdyLax−yMgxAl12−xO19 (ASL:Nd) crystals give efficient F43/2→I49/2 laser emission at 900 nm, whose properties depend on the x and y composition parameters. Based on high-resolution spectroscopy and emission decay, this paper demonstrates that the composition dependence of the laser emission is caused by the presence of two structural centers, C1 and C2, whose relative proportion in crystals is determined by composition parameter x. From the spectral data and crystal structure it is inferred that C2 center that prevails at low x, corresponds to a Nd3+ in a Sr2+ (2d) site of D3h local symmetry with no nearby Ln3+ (La3+ or Nd3+) ions. The C1 center lines, prevailing at large x parameter, which are broader and shift with composition, are composite lines of various structural centers of Nd3+ in a Sr2+ site with different occupancy of nearest-neighbor sites by Ln3+. The influence of the spectral and emission dynamics features of these centers on the laser properties is discussed and criteria for the selection of optimal composition is inferred.

Spectroscopic investigation of Nd 3+ in ASL

“…The absorption spectra of ASL: Nd, recorded in unpolarized light with propagation along the c-axis, show additional features to those previously investigated [4,5], such as the splitting of C 2 lines in the samples with very low x values as shown in Fig. 1.…”

“…The main characteristics of the spectra are: -The two main centers structure, C 1 and C 2 observed previously [4,5], remains in all investigated composition range; at small x C 2 center is prevailing, while at large x (x=0.5) C 1 center is dominant.…”

“…3 where the new samples data follow the tendency observed previously for the x=0.2 -0.4 range (data for x=0.05-0.5 refer to y=0.05). The relative intensity is practically independent on the Nd 3+ content [5]. Relative intensity Neglecting the small splitting of C 2 lines, the barycenters of the 2S+1 L J manifolds are similar for the two main centers and the lines are almost coincident in 2 P 1/2 .…”

“…Recent spectroscopic investigations [4,5] of ASL: Nd with 0.2≤x≤0.4 have revealed the presence of two structural centers, C 1 and C 2 , whose proportions are determined by the composition parameter x: C 1 dominates at high x, while C 2 at low x. The spectroscopic properties (line positions, shapes and widths) of these centers depend on x, mainly for C 1 .…”

Czochralski growth and characterization of neodymium-doped strontium lanthanum aluminate (ASL:Nd) single crystals

“…The complex composition of ASL:Nd crystals and the distribution of various cations in specific sites (La 3+ and/or Nd 3+ in Sr 2+ sites and the charge compensating ion Mg 2+ in the trivalent Al 3+ cationic sublattice) can induce a large variety of non-equivalent Nd 3+ ions sites exhibiting different optical spectra. The presence of two basic structural centers of Nd 3+ in ASL, with different static and dynamic spectral characteristics, has been reported recently [10]. The relative intensities of absorption bands associated with these centers are composition dependent: the intensity of C 1 absorption band increases with the composition parameter x, while the intensity of C 2 absorption band decreases.…”