Luminescence and energy transfer in La2O3–Nb2O5–B2O3:M3+ (M=Bi, Eu, Dy) glasses

Abstract

The luminescence and energy transfer processes in La 2 O 3-Nb 2 O 5-B 2 O 3 :M 3+ (M=Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy (excitation and emission, down to 4.2 K) and decay time measurements at room temperature. The observation of niobate luminescence implies a considerable degree of short-and intermediaterange order in these glasses. Energy transfer from the niobate groups to the lanthanide ions was observed for Eu 3+ , but not for Dy 3+ , suggesting that the energy transfer process occurs to the charge-transfer state of the Eu 3+ ion, rather than to its f-levels. Inter-Eu 3+ energy transfer was negligible in the concentration range investigated (up to 3 mol%). In contrast, cross-relaxation processes between Dy 3+ ions were active at concentrations as low as 0.5 mol%. In the Bi 3+ doped glasses the energy transfer was observed from the Bi 3+ excited levels to the oxygen deficient niobate groups.

A structural model of La2O3–Nb2O5–B2O3 glasses based upon infrared and luminescence spectroscopy and quantum chemical calculations

“…In addition to these results obtained for the 28La 2 O 3 -10Nb 2 O 5 -62B 2 O 3 sample, Table 2 presents the luminescence results for other samples from our previous work [8] as well as for three other crystalline niobates.…”

“…In our previous work, we observed a relationship between the luminescence and the sample composition [8]. Crystalline niobate were used as model systems for extrinsic sub-networks in glasses structures.…”

“…The increase of La 2 O 3 concentrations at 25 mol% seems to disrupt these chains of niobate edge-sharing into corner-sharing off-center units. This leads to structural changes that are reflected into the luminescence properties [8].…”

An ab initio cluster-in-lattice model for the luminescence of K2NbOF5 crystal

“…Configuration interaction with single replacements (CIS) [14], time-dependent (TD) or polarization propagator (RPA) with Hartree-Fock (TD-HF) or hybrid functional density (TD-B3LYP) reference functions [15][16][17][18][19], and complete active space (CAS) [20][21][22] approaches have been used to calculate the electronic structure of the ground and lowest singlet and triplet excited states. The active space of the CAS method consisted of the three highest doubly occupied (HOMO, HOMO À 1, HOMO À 2) and two unoccupied (LUMO, LUMO + 2) molecular orbitals CAS (6,5). This active space was selected based upon the orbital symmetry, the optimization of the CAS wavefunction and practical viability of performing these calculations on larger systems.…”

“…Particularly, these materials usually have well ordered crystalline structures so that the quenching of the intrinsic luminescence by extrinsic centers is avoided and thus increasing their luminescence efficiencies [1][2][3]. It was thus very surprising when the luminescence of niobates were observed, for the first time, in borate-lanthanum glasses [4][5][6]. These observations have prompted us to develop a structural model for these glasses, which could explain their luminescence.…”