Influence of microscopic defects on optical damage resistance of Zn:Fe:LiNbO3 crystals

Abstract

Influence of defect structure on the infrared transmission spectra of OH -in Zn:Fe:LiNbO 3 crystals with various ZnO concentration and different Li/Nb ratios was investigated. It indicates that above the Zn concentration threshold the OH -absorptions bands successively shift from 3482cm -1 to 3504cm -1 and 3529cm -1 . The intensity of the 3504cm -1 band increases with ZnO concentration increasing. The optical damage resistance of the Zn:Fe:LiNbO 3 crystals increases rapidly when the ZnO concentration exceeds a threshold value. This result contributed to the site alteration from the Li sites to Nb sites due to Zn-doping in crystal.

No difference in local structure about a Zn dopant for congruent and stoichiometricLiNbO3

“…For LNO, adding dopants such as Zn, Mg, In, etc. suppresses the photorefractive response, making the material much more resistant to optical damage 2,3 . In order to model mechanisms for photorefraction suppression, the dopant site(s) needs to be determined and the extent of distortion about them measured.…”

EXAFS evidence for a primary ZnLidopant in LiNbO3

“…If the number of neighbors was allowed to vary, it was reduced towards zero. When we attempted to include significantly more Zn neighbors (1)(2)(3), the fit quality decreased further. Thus the number of Zn neighbors is <1 and any clustering of Zn atoms is small.…”

“…Surprisingly the strongest Zn-O is only slightly weaker than the Nb-O2 bond. For LiNbO 3 Megaw 41 noted that the Li-O bonds are much weaker than the Nb-O bonds and viewed the structure as formed of corner sharing NbO 6 octahedra. Such a structure is very flexible if the Li-O bonds are weak.…”

“…2 Many of these properties can be modified or controlled by specific dopants. For example, when dopants such as Mg, Zn, In, or Hf are incorporated in LNO, the material becomes more resistive to optical-damage, 3,4 i.e., a decrease in its photorefractive response appears, and then one can take advantage of its other properties such as optical frequency conversion (second harmonic generation). 5 However, to fully understand the microscopic mechanisms for the suppression of the photorefractive effect and to determine the precise nature of donors and acceptors, the dopant site location (on Li + or Nb +5 ) and the local environment about the active transition-metal impurities has to be elucidated.…”

“…There have been many efforts-both theoretical [5][6][7][8][9][10][11][12][13][14] and experimental 3,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] -to investigate intrinsic and extrinsic defects. For undoped, congruent LNO each antisite Nb 6 Adding divalent and/or trivalent metal dopants produces extrinsic defects that modify important optical properties and also change the lattice constants, 17,30 particularly near and above the so-called threshold concentration of ∼7 mol %.…”