Photoluminescence Spectral Change in Layered Titanate Oxide Intercalated with Hydrated Eu³⁺

Abstract

A number of interesting photoluminescence properties of titanate layered oxide intercalated with hydrated Eu3+ have been demonstrated. Photoluminescence intensity of Eu3+ decreased rapidly with time during irradiation by UV light having energy higher than the band gap energy of the host TiO (Ti(1.81)O4) layer. This is presumably due to the decrease in energy transfer from the host TiO layer to Eu3+ as a result of the change in the hydration state of water molecules surrounding Eu3+, which is caused by the hole produced in the TiO valence band. When irradiation was discontinued, the emission intensity gradually recovered. The recovery time increased when the water in the interlayer is removed by heat treatment. This indicates that the state of interlayer water changes during irradiation and returns to its initial state after discontinuation of irradiation. The excitation spectra changed drastically at any given wavelength upon irradiation with UV light. A comparison of the excitation spectra before and after irradiation reveals that only the excitation peak at around the irradiation wavelength decreased upon irradiation, as in the case of spectral hole burning. The hydration state of water molecules surrounding Eu3+ presumably changes depending on the irradiation wavelength, leading to the above spectral change because the Eu/TiO film has a superlattice structure producing holes with different energies.

Photoluminescence of nanosheets doped with rare earth ions

“…In the other group, the guest ions are inserted into the transition metal oxide nanosheets to form the phosphors [7][8][9][10][11][12][13]. In this system, effective energy transfer from the transition metal oxide nanosheet hosts to Ln luminescence activators may take place.…”

“…Among the photoactive components, Tb 3+ and Eu 3+ are particularly interesting because of their strong and well-defined green or red photoluminescence property, while one of the candidate host nanosheets for such an ideal phosphor material is TiTaO 5 − nanosheet, which could be easily fabricated by the soft chemical exfoliation described below. It must point out that the stabilities of photoluminescence properties and the efficiency of energy transfer tend to be susceptible to the amount of the cointercalated species [12][13][14].…”

Dynamic Control of Photoluminescence for Self‐assembled Nanosheet Films Intercalated with Lanthanide Ions by Using a Photoelectrochemical Reaction

“…For example, the titanate layered oxide intercalated with Eu 3+ ions prepared from titanate nanosheets and Eu 3+ ions has unique luminescence properties. [9][10][11] The layered oxide gives a red emission from the Eu 3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet, [9,10] and the emission from the Eu 3+ ions is promoted by intercalated water molecules.[10] Furthermore, spectral hole burning caused by the intercalated water molecules was observed in the excitation spectra at room temperature. [11] Nanosheets of TiO x , NbO x , and TaO x give a high photocurrent during the photoelectrochemical reaction under UV illumination with an energy higher than that of the bandgap.…”

“…[9][10][11] The layered oxide gives a red emission from the Eu 3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet, [9,10] and the emission from the Eu 3+ ions is promoted by intercalated water molecules.…”

“…These were attributed to the bandgap excitation in the nanosheets. [9][10][11][18][19][20][21][22][23][24][25] The energy released during excitation of the bandgap under UV illumination is transferred to the intercalated Ln 3+ ions (energy transfer), which induces their specific emissions (Eu 3+ : red and Tb 3+ : green). By contrast, no emission was observed in the case of a cathodic bias.…”