Syntheses and luminescence of complete solid solutions Gd_1−xEu_x[B₆O₉(OH)₃] and α-Gd_1−xEu_xB₅O₉

Abstract

There are very few luminescence studies for rare earth borates with hydroxyl or crystalline water molecules, which were believed to have a low luminescence efficiency because the vibrations of -OH or H 2 O may lead to quenching of the emission. We were motivated to study the luminescence properties of Gd 1Àx Eu x [B 6 O 9 (OH) 3 ] (x = 0.10-1) and their dehydrated products, a-Gd 1Àx Eu x B 5 O 9 . Efficient energy transfer from Gd 3+ to Eu 3+ was found in all of the studied polyborates. By TG-DSC and powder XRD experiments, we observed the dehydration of Eu[B 6 O 9 (OH) 3 ], the re-crystallization to a-EuB 5 O 9 , and further decomposition to a-EuB 3 O 6 . During those processes, the Eu 3+ luminescence spectra show interesting variations, meaning it is a good medium to understand the coordination environment evolution of Eu 3+ . It is observed that the symmetry of the Eu 3+ coordination environment is the lowest in the amorphous state. Interestingly, this amorphous phase possesses a high efficiency of f-f transitions and a large R/O value (4.0), which implies its potential as a good red-emitting UV-LED phosphor. Anhydrous a-EuB 5 O 9 shows the highest luminescence efficiency when excited by Eu 3+ CT transition. For the first time, complete solid solutions a-Gd 1Àx Eu x B 5 O 9 were synthesized directly by the sol-gel method, and their luminescence properties were also studied.

Sol–gel syntheses, luminescence, and energy transfer properties of α-GdB5O9:Ce3+/Tb3+ phosphors

“…Similar phenomena have been observed in α-Sm 1−x Eu x B 5 O 9 and α-Gd 1−x Eu x B 5 O 9 (λ ex = 392 nm). 19,20 This is reasonable because the Tb 3+ ions are well separated by pentaborate groups. 10 If excited by 273 nm irradiation (Gd 3+ absorption), the emission intensity increases with Tb 3+ content first and reaches a maximum value when x = 0.30 (see Fig.…”

“…In fact, the phosphors prepared by the sol-gel method give a superior luminescence intensity due to their high homogeneity and crystallinity. 19,20 It becomes apparent that α-LnB 5 O 9 is a good host material for luminescence applications because the large polyborate anions prevent the concentration quenching, and all the samples investigated up to now show strong emission profiles. 10,20 It is interesting to study the performance of another important activator, Tb 3+ , in this host.…”

“…19,20 It becomes apparent that α-LnB 5 O 9 is a good host material for luminescence applications because the large polyborate anions prevent the concentration quenching, and all the samples investigated up to now show strong emission profiles. 10,20 It is interesting to study the performance of another important activator, Tb 3+ , in this host. α-TbB 5 O 9 has been reported, 10 which gives an indication of the easy substitution of Tb 3+ into α-LnB 5 O 9 .…”

“…19,20 In addition, the solgel method was also employed to prepare complete α-Ln 1−xEu x B 5 O 9 (Ln = Sm and Gd) solid solutions, noting that the traditional solid state reaction method would always lead to a mixture of α-Ln 1−x Eu x B 5 O 9 and orthoborates/metaborates. In fact, the phosphors prepared by the sol-gel method give a superior luminescence intensity due to their high homogeneity and crystallinity.…”

Syntheses and luminescence of La1−xEux[B8O11(OH)5] and β-La1−xEuxB5O9 (0 ≤ x ≤ 0.135)

“…17,18 It allows the following investigations on the luminescence of those new polyborates. 19,20 On the other hand, the calcination of hydrous polyborates usually leads to the formation of new polyborates other than three already-reported anhydrous rare earth borates. 19,20 On the other hand, the calcination of hydrous polyborates usually leads to the formation of new polyborates other than three already-reported anhydrous rare earth borates.…”