Crystalline structure and optical spectroscopy of Er3+-doped KGd(WO4)2 single crystals

Abstract

Abstract. KGd(WO 4 ) 2 single crystals doped with Er 3+ have been grown by the flux top-seeded-solution growth method. The crystallographic structure of the lattice has been refined, being the lattice constants a = 10.652(4), b = 10.374(6), c = 7.582(2) Å, β = 130.80(2)• . The refractive index dispersion of the host has been measured in the 350-1500 nm range. The optical absorption and photoluminescence properties of Er The technological interest in the development of solidstate lasers for application in long-distance optical communications has promoted the study of laser ions with an emission close to the minimum of the optical losses in silica fibers, namely 1.5 µm. The present development of a new laser generation requires us to find crystals with low excitation threshold and suited to be excited by the emission of diode lasers. Er 3+ only has weak absorption bands in the 600-1000 nm region, but its photoluminescence can be sensitised by energy transfer from Yb 3+ , which shows a strong optical absorption in the 900-1000 nm range. This region overlaps the emission of InGaAs diode lasers. As a matter of fact, InGaAs diodepumped room-temperature laser operation has been recently demonstrated in KGd(WO 4 ) 2 :Yb:Er crystals [7] (hereafter KGd(WO 4 ) 2 is abbreviated as KGW), however the efficiency of the process was weak and the physical processes involved were poorly understood. Moreover, Er has been used to sensitise the Tm 3+ emission in KGW crystals at liquid nitrogen temperature [8].Despite the relevance of the optical properties of Er 3+ in KGW crystals, its spectroscopic properties have been reported at 77 K only for the 4 S 3/2 or lower energy levels [9,10]. The present work reports a spectroscopic study of the Er 3+ ions incorporated in KGW crystals grown by the flux top-seeded-solution growth (TSSG) technique.KGW crystals have been also used as a laser host for Nd 3+ ions because of the high efficiency of the 4 F 3/2 → 4 I 11/2 transition [11,12] as well as a host for other rare-earth laser ions [8]. Recently, some research has focused attention on crystals with relevant cubic nonlinearity χ (3) because with these materials it is possible to obtain unconventional lasers, such as lasers with stimulated-Raman-scattering (SRS) frequency self-conversion. The KGW:Nd possesses an effective cubic nonlinearity of about 10 −13 esu and presents a good efficiency in the process of SRS self-conversion [13].In view of the relevance of the KGW lattice host, we have also performed a refinement of the crystal structure, in order to improve the currently known lattice constants and to help in the discussion of the local lattice site symmetry when required. Further, we discuss the orientation of the indicatrix of the crystal with regards to the crystallographic axes and we have obtained the value of the refractive indices in a wide spectral region.

Sensitization ofEr3+emission at1.5μmbyMateos1, Pujol2, Güell3 et al. 2002Phys. Rev. BSelf Cite

“…From these two observations we conclude that the crystal field of KYbW is stronger than in KGW, which agrees well with smaller interatomic distances 22 Yb-Yb presented in KYbW than 11 the distances Gd-Gd, presented in KGW. 18 Also, the Judd-Ofelt parameters of erbium in KYbW ͑calcu-lated later͒ and those of KGW, 21 showed the influence of this crystal field, in which the Judd-Ofelt parameters of KYbW were larger than those of KGW.…”

“…We compared the energy position of the center of gravity of each multiplet of Er 3ϩ in KGd(WO 4 ) 2 ͑KGW͒, 21 and KYbW hosts. We found that the difference between these centers of gravity was smaller in KYbW crystals.…”

Conical refraction: fundamentals and applications

“…The CR semi-angle α depends on the principal refractive indices of the crystal as α = (n 2 2 − n 2 1 )(n 2 3 − n 2 2 )/n 2 2 , where we have assumed n 1 < n 2 < n 3 . For the KGd(WO 4 ) 2 ) biaxial crystals that we will use in all our experiments, α(λ = 633 nm) = 16.9 mrad [33,60].…”

Thermal conductivity of Nd3+ and Yb3+ doped laser materials measured by using the thermal lens technique

“…The Nd-doped KGW biaxial crystals were also prepared in the form of platelets, but with the faces perpendicular to their principal axis b. In this case, light could be polarized with the electric field parallel to one of the other optical indicatrix axes labelled n m and n g , or X and Z, with b = Y = n p [18].…”