Optical study of Cr3+-doped LaSc3(BO3)4 crystal

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Abstract

This paper reports on the optical properties of Cr3+-doped LaSc3(BO3)4 (Cr3+:LSB). Based on measurement of the absorption spectrum the crystal field strength Dq, the Racah parameters B and C were calculated. The photoluminescence spectrum of Cr3+:LSB via 4T24A2 transition is a broadband emission from 740 to 1280 nm at room temperature. The measurements of absorption and photoluminescence spectra show that in Cr3+:LSB the Cr3+ ions occupy weak crystal field sites.

Introduction

There remains considerable research interest in the physics of tunable solid-state laser gain media. The focus of such interest is to expand the available pump and output wavelength of potential tunable laser, to develop more suitable pumping schemes especially those using flash-lamp and diode-laser as sources of pump radiation, and to enhance transition rates leading to greater laser efficiencies. The double borates RX3(BO3)4 (R=Y, Gd, La, X=Al, Ga, Sc) are isostructural with the mineral huntite CaMg3(CO3)4 [1], which can provide suitable sites for substitution by trivalent rare earth ion or trivalent transition metal ions in larger dopant concentration than in other crystals because of weaker luminescence quenching in this crystal structure [2], [3], [4], [5]. Their excellent physical and chemical properties give RX3(BO3)4 crystals significant potential as a gain media. The Cr3+- or Ti3+-doped YAl3(BO3)4 (YAB), GdAl3(BO3)4 (GAB), YSc3(BO3)4 (YSB) and GdSc3(BO3)4 (GSB) crystals as tunable laser materials have been reported several years ago [6], [7], [8]. The Nd3+-doped LaSc3(BO3)4, another member of RX3(BO3)4 family, was reported as a high-efficient laser material for diode-pumped [9]. In fact, the LaSc3(BO3)4 can also provide suitable sites for Cr3+ substituting Sc3+ ions to give rise to vibronic emission as well as the YAB, GAB, YSB, GSB. This paper reports preliminary optical study of Cr3+-doped LaSc3(BO3)4 (Cr3+:LSB) crystal.

Section snippets

Experimental details

Cr3+:LSB was grown by the Czochralski method. The stoichiometrically mixed raw materials of La2O3, Sc2O3; Cr2O3 and B2O3 were molten in a crucible in N2 atmosphere. The Cr3+:LSB crystal was grown at a pulling rate of 1 mm/h and a rotating rate of 10 rev./min. The Cr3+:LSB crystal having diameter 15 mm and length 35 mm was obtained. The Cr3+ concentration was determined to be 3at.% by electron probe microanalysis. A sample of an arbitrary direction measuring 2.67×3×4 mm3 was cut from the

Results

The optical absorption spectrum of Cr3+:LSB crystal measured at 300 K is shown in Fig. 1. The dominant features of absorption spectrum are two broad bands with peaks at 457 nm due to the 4A24T1 transition and at 654 nm due to the 4A24T2 transition, respectively. The R lines from the spin-forbidden 4A22E transition in Cr3+:LSB crystal were not observed. The dip near 678 nm in the 4T2 band is characteristic of low crystal field Cr3+ hosts, which is also seen in ScBO3 [10], KZnF3 [11] and SrAlF5

Discussion

The purpose of the present optical study of Cr3+:LSB crystal is to assess its suitability as a potential tunable laser gain media. The absorption and photoluminescence spectra arise out of the weaker crystal field in Cr3+:LSB. Chromium ions in the Cr3+:LSB crystal are situated in a weak crystal field where the 4T2 state is the lowest. In Cr3+:LSB the 4A24T1,4T2 broad absorption bands cover much of the visible region, which are ideal for flash-lamp pumping. Of course, the major interest in new

Acknowledgements

This research was supported by the Key Project of Science and Technology of the Fujian Province (No.2001H107) and The Natural Science Foundation of China (No. 59972037), respectively.

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