A model of the capture volume of free carriers in fluorophosphate glasses doped with terbium

Abstract

INTRODUCTIONThe particular interest expressed by researchers in the study of the behavior of rare-earth ions in glassforming matrices has stemmed, to a large extent, from new possibilities offered by optical fiber amplifiers based on Er 3+ , Pr 3+ , and Nd 3+ ions [1,2]. Until recently, many attempts have been made to elucidate the nearest environment of dopant ions and to determine their spatial distribution in different matrices [3][4][5]. In our opinion, investigation into the properties of fluorophosphate and fluoride glasses doped with rare-earth ions holds the greatest interest today. This is associated with the unique spectroscopic properties exhibited by rare-earth ions in these matrices (specifically with the high efficiency of excitation energy transfer from Yb 3+ ions to Er 3+ ions as compared to silicate and borate matrices [6,7]), on the one hand, and with the low energy of phonons in the fluoride matrix (which makes it promising for use in fabricating fibers with low losses in the IR range [1, 2]), on the other hand.Traditionally, the local environment of dopant ions has been examined using spectroscopic methods, including the study of luminescence spectra, luminescence decay kinetics, and IR absorption spectra. In particular, Hiroyuku et al. [8] investigated the Eu 3+ luminescence spectra of fluoroaluminate and fluorophosphate glasses (containing 1 mol % EuF 3 ) at 80 K and revealed that the nearest environment of Eu 3+ ions involves oxygen. Kolobkov et al. [9] refined the dependence of the local environment of rare-earth ions in glasses of the MgF 2 -(0.6CaF 2 + 0.4AlF 3 )-Ba(PO 3 ) 2 system on the content of the fluoride component in the initial matrix. In [9], the authors analyzed the Eu 3+ and Nd 3+ luminescence spectra and nonradiative nonresonant energy transfer between Er 3+ and Ho 3+ ions and established that, in fluorophosphate glasses containing up to 40-50 mol % of fluorides, the nearest environment of rare-earth ions is predominantly formed by phosphate groupings. In this case, the dopant content was equal to 1 wt % (5 wt % for Eu 2 O 3 ). More recently, Zhmyreva et al.[10] studied the vibronic and Raman spectra of doped glasses in systems with a similar composition (the Eu 2 O 3 content was 5 wt %). It was shown that the presence of fluorophosphate groups in the vicinity of rare-earth ions manifests itself in the spectral characteristics of glasses containing 30 and 10 mol % of barium metaphosphate and that, at a higher barium metaphosphate content, the dopant ions are incorporated into regions in the immediate vicinity of the phosphate structural units of the glass network. Karapetyan et al. [11] observed the concentration quenching of neodymium luminescence in glasses of the MgCaSrBaAl 2 F 14 -Ba(PO 3 ) 2 pseudobinary system. It was found that the concentration quenching limits for glasses containing 60 and 7 mol % Ba(PO 3 ) 2 are equal to 2 × 10 20 and 1 × 10 20 ions cm -3 , respectively. Comparison of the results obtained with the data on the absorption spectra allowed those aut...

Local environment of Eu3+ and Tb3+ ions in fluorophosphate glasses of the Ba(PO3)2-MgCaSrBaAl2F14 system

“…With the aim of elucidating how small additions of rare-earth ions affect the structure of fluorophosphate glasses over a wide concentration range, we used an indirect method; more precisely, we studied the induced optical absorption and EPR absorption spectra of glasses, as was done earlier in [5,6,15]. Figure 2a shows the induced optical absorption spectra of the 40Ba(PO 3 ) 2 · 60MgCaSrBaAl 2 F 14 glasses doped with terbium fluoride at different concentrations.…”

“…It is known that the selective incorporation of dopant ions into local regions of the glass matrix occurs in a number of oxide glasses, such as silicate [2], borosilicate [3], and germanate [4] glasses; in the very recent past, there have appeared papers reporting on the occurrence of segregation phenomena in fluorophosphate glasses [5,6]. Nowadays, fluorophosphate glasses have found a wide application in many fields of engineering, for example, as materials for fiber-optics communication systems [7], optical fiber amplifiers [8,9], and matrices used for the generation and investigation of quantum-confinement effects [10].…”

“…In this respect, the elucidation of the distribution of rare-earth ions in the fluorophosphate host remains an important problem. As a rule, the objects of investigation are rare-earth ions contained in glasses at concentrations ranging from 0.01 to 5.00 mol % for rare-earth fluorides [6,11]. At lower concentrations, rare-earth element and transition metal ions have been considered as impurities that can affect the properties of glasses.…”