Room-temperature Persistent Spectral Hole Research Articles

Synthesis and Optical Properties of Calcium Halide-Based Aluminoborate Glasses Codoped with Eu2 + and Eu3 + Ions

Oxy-halide glasses in systems of –– ( = F, Cl, and Br) doped with were prepared by a melt quenching method and their optical properties were characterized by measurements of UV-visible luminescence, hole burning, and electron spin resonance (ESR) spectra. For the - and -based samples, ions were partially reduced during the heating process in ambient atmosphere, so that room temperature persistent spectral hole burning was observed on them. Meanwhile, no obvious band emission or characteristic ESR signal of ion was recorded on the -based samples also prepared in ambient atmosphere, and consequently any hole peak was hardly detected even at . However, hole peaks were produced and persisted at room temperature on the -based samples remelted in a reducing atmosphere. The self-reduction mechanism for ion in the - and -based samples is discussed as well as the hole formation in all samples.

Role of Eu ions and defect centers in formation of high-temperature persistent spectral holes in glass

The mechanism of room temperature persistent spectral hole burning was investigated using Eu-doped sodium borate glass (35Na 2O–65B 2O 3). The concentrations dependence of defect centers on the extent of hole burning was investigated for several Eu concentrations because the mechanism proposed so far are of two types: electron transfer to Eu 3+ from Eu 2+ and from defect centers in the glass. When the defect concentration increased due to X-ray irradiation, a high-temperature hole burning was observed at a Eu concentration (0.3 mol%) ; where the phenomenon is not observed in a normal sample without X-ray irradiation. When the Eu concentration was very low (0.1 mol%) , a spectral hole was observed only at low temperatures even when the concentration of defect centers became saturated due to X-ray irradiation. Furthermore, a concentration quenching of fluorescence from Eu 3+ became obvious at Eu concentrations of more than ca. 1 mol% . Hole burning became obvious at the same concentration. These findings indicate that the mechanism is an energy transfer from selectively excited Eu 3+ to adjacent Eu 2+ and subsequent electron transfer from Eu 2+ to Eu 3+. Defect centers in the glass reduce the barrier height of this electron transfer.

Mechanism of the room-temperature persistent spectral hole burning in borate glasses doped with Eu3+

Spectroscopic properties and room-temperature persistent spectral hole burning mechanisms of Eu3+-doped borate glasses were investigated. The depth of the burnt hole increased with the amount of carbon powders (i.e., degree of reducing atmosphere). This was attributed to the formation of defects which can donate free electrons for the photoreduction of Eu3+→Eu2+. Holes survived >104 s at 20 K and approximately 40% of hole areas were preserved after annealing at 280 K. The photoreduction of Eu3+ to Eu2+ is a primary mechanism of hole burning and this hypothesis was supported by spectral hole properties, relaxation properties as well as changes in the local structure of Eu3+ in glasses.

Room temperature persistent spectral hole burning of Eu 3+ ions doped in sol–gel derived glasses

The persistent spectral hole-burning (PSHB) phenomenon was investigated for Eu 3+-ion-doped Al 2O 3–SiO 2 glasses prepared by the sol–gel method. The efficiency of hole burning, burned at low temperature ∼77 K, was proportionally increased with the content of OH groups surrounding the Eu 3+ ions. The proposed mechanism for hole burning is the optically activated rearrangement of the OH bonds surrounding the Eu 3+ ions. The burned hole was thermally refilled and erased above ∼200 K. On the other hand, the glass irradiated with X-rays showed PSHB up to room temperature. It is considered that the hole is formed by electron transfer between the Eu 3+ ions and the excited Eu 3+ or defect centers. The lifetime of the hole was estimated as ∼1.5×10 5 s at 200 K.

Defect centers and room temperature persistent spectral hole burning in X-ray irradiated Eu 3+-doped glass

We have investigated the room temperature persistent spectral hole burning of X-ray irradiated Eu 3+-doped Al 2O 3SiO 2 glass, prepared by heating at 1000°C and then glasses. The sol–gel-derived Eu 3+-doped glass heated in air at 800°C and irradiated with X-ray exhibits the hole spectra at room temperature, while on the other hand no hole is formed in the glass heated at 1000°C. We can attribute these differences to the different formation of the defect centers by the X-ray irradiation. The formation of the activated Eu 3+ ions together with the oxygen defect centers plays an important role on the room temperature hole burning. The lifetime of the burnt hole is estimated to be ∼1.5×10 5 s at 200 K.

Room temperature persistent spectral hole burning in x-ray irradiated Eu3+-doped borate glasses

Irradiation of x-rays has induced room-temperature persistent spectral hole burning (PSHB) in Eu3+-doped borate glasses melted under an inert atmosphere. Defects were formed by x-ray irradiation and these defects, especially electron trapping centers near rare-earth ions in glasses, were responsible for the PSHB. Electrons were released from these defects upon irradiation of a burning light. Photoreduction of Eu3+ to Eu2+ by trapping these electrons resulted in the formation of persistent spectral holes.

Room-temperature persistent spectral hole burning ofEu3+coupling withAl3+in glass

Room-temperature persistent spectral hole burning was observed in ${\mathrm{Eu}}^{3+}\ensuremath{-}\mathrm{d}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{d}$ ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}{\ensuremath{-}\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$ glasses. The sol-gel-derived ${\mathrm{Eu}}^{3+}\ensuremath{-}\mathrm{d}\mathrm{o}\mathrm{p}\mathrm{e}\mathrm{d}$ glasses were heated in hydrogen gas and irradiated with x ray, in which the oxygen deficient centers were induced in Al-O bonds and some ${\mathrm{Eu}}^{3+}$ ions were reduced into ${\mathrm{Eu}}^{2+}$ by heating in hydrogen gas. The spectral holes were burned in the excitation spectra of the ${}^{7}{\stackrel{\ensuremath{\rightarrow}}{{F}_{0}}}^{5}{D}_{0}$ transition of ${\mathrm{Eu}}^{3+}.$ The maximum depth of the hole burned at room temperature was found to be $\ensuremath{\sim}10%$ of the total excitation intensity for both the glasses and independent of the treatment conditions of glasses. A proposed model for hole burning is the excitation of the ${\mathrm{Eu}}^{3+}$ ion and subsequent hole trapping in the oxygen-defect centers in the Al-O bonds. The burnt holes were easily erased by laser irradiation with the energy different from burning one.

Room-temperature persistent spectral hole burning of x-ray-irradiatedSm3+-doped glass

We report on persistent spectral hole burning in the x-ray-irradiated Sm3+-doped fluoroaluminate glasses at room temperature. 0.1SmF3·14.9YF3·10MgF2·20CaF2 10SrF2·10BaF2·35AlF3 (mol%) glass was prepared underan Ar + NF3 (5 vol.%) atmosphere. Absorption andphotoluminescence spectra showed that some of the Sm3+ ions in theglass sample were reduced to Sm2+ ions after the x-ray irradiation.The hole was burned in the 7F0-5D0 line of the Sm2+ ions by means of a DCM dye laser. No antihole or increasedexcitation (absorption) peak was observed around the burned hole. It wasconcluded that the persistent spectral hole burning was formed by theoptically activated recombination of the electrons trapped by the Sm3+ ions with the trapped holes.

Room-temperature persistent spectral hole burning in Eu 3+-doped inorganic glasses: the mechanisms

High-temperature persistent spectral hole burning (PSHB), up to room temperature, has been observed in a Eu 3+-doped aluminosilicate glass and in a lanthanum-aluminosilicate one. The emphasis here is on trying to understand the mechanism(s) leading to such a process and the effects due to changes in glass composition. Spontaneous refilling measurements show that at least two mechanisms, a very slow one and a faster one, are involved. The “faster” or “easy” component may correspond to a local structural rearrangement of the host and/or to photoreduction of the Eu 3+ ions. We suggest that the slow component, leading to very stable photoproducts, corresponds to transfer of an electron over a sizable distance through a multi-step process. PSHB in the lanthanum-aluminosilicate sample requires larger irradiation doses but leads to more stable spectral holes. This observation is discussed, which leads us to raise the question as to whether there should be a trade-off between easiness and stability.

Room-temperature persistent spectral hole burning of Sm 2+ in silica-based fibers

Persistent spectral hole burning has been observed successfully at room temperature in the excitation spectrum for the 7 F 0− 5 D 0 transition of Sm 2+ in silica-based fibers co-doped with Al. The room-temperature persistent spectral hole burning is reported for the first time, to the best of our knowledge, in Sm 2+-doped fiber. The hole width was measured to be about 6 cm −1. The ratio of inhomogeneous to homogeneous linewidths of this system is ∼15.

Room-temperature persistent spectral hole burning of Eu^3+ in sodium aluminosilicate glasses

Persistent spectral hole burning has been observed at 77 K, 180 K, and room temperature for Eu(3+) in sodium aluminosilicate glass melted under a reducing atmosphere. In particular, room-temperature persistent spectral hole burning is reported for the first time to our knowledge in Eu(3+) -doped materials. The persistent hole is accompanied by no antiholes and lasts for 1 h at least. The thermal stability of the hole is greater than that of a persistent hole burned for Eu(3+) in sodium aluminosilicate glass melted in air.

Room temperature persistent spectral hole burning in neutron-irradiated IaB-type diamond

After annealing a heavy dose neutron-irradiated type IaB diamond at 950°C, we observed two new color centers of defect aggregates in the near infrared spectral range. With a cw Ti-sapphire laser, we obtained persistent spectral hole burning at room temperature in the zero-phonon lines of both centers at 774 and 813 nm.

Room temperature persistent spectral hole burning of Sm 2+ in fluorohafnate glasses

Persistent spectral hole burning of Sm 2+ in a glass system at room temperature was observed. The hole was burned at 680.3 nm with 230 mW laser light and was observed via the excitation spectrum. In this system a photochemical process is likely to be dominant because of the absence of an anti-hole adjacent to the hole.