The paper presents the first observation of photoluminescence spectra of V3+ impurity in SrTiO3. The broad band of the observed emission is located in the near IR region and at low temperatures consists of a pronounced zero-phonon line (ZPL) with a maximum at 1157.1 nm (8642 сm-1) at 77 K and developed vibronic sidebands extending to 1450 nm. The observed ZPL is associated with an intracenter 1T2g → 3T1g or a closely located 1Eg → 3T1g emission transition in V3+ (3d2) ions replacing Ti4+ ions. It was found that the temperature shift of zero-phonon line is unusually large and its frequency decreases upon lowering the temperature. The local configuration instability of V3+ ions in the 3T1g ground state caused by soft TO1 temperature-dependent phonon mode present in SrTiO3 is considered as a possible source of the observed unusual temperature shift.

Photoluminescence (PL) of Er3+ ions embedded in GaLaS(O) glass at excitation wavelengths of 488, 532, 660, 808, and 980 nm has been studied. Typical cases at which the ratios of the optical transition intensities have no dependence on the pumping intensity have been considered. For the case of pumping at the 488 nm wavelength the method of extrapolation coefficients, which reveals the up-conversion nature of PL "mimicking" a "normal" PL, has been demonstrated. The thermal coupling of S3/24 and H11/22 manifolds, which are responsible for the intense PL in the green region of the visible spectral range, is discussed.

The paper presents the first observation of photoluminescence spectra of V3+ impurity in SrTiO3. The broad band of the observed emission is located in the near IR region and at low temperatures consists of a pronounced zero-phonon line (ZPL) with a maximum at 1157.1 nm (8642 cm–1) at 77 K and developed vibronic sidebands extending to 1450nm. The observed ZPL is associated with an intracenter 1T2g → 3T1g or a closely located 1Eg → 3T1g emission transition in V3+ (3d2) ions replacing Ti4+ ions. It was found that the temperature shift of zero-phonon line is unusually large and its frequency decreases upon lowering the temperature. The local configuration instability of V3+ ions in the 3T1g ground state caused by soft TO1 temperature-dependent phonon mode present in SrTiO3 is considered as a possible source of the observed unusual temperature shift.

We present a study of KTaO3:Er (approximate to 0.05%) single crystals based on a multifaceted approach including the use of optical absorption, far-infrared reflectivity, electron paramagnetic resonance, photoluminescence spectra, and ab initio simulations. We describe briefly the fundamental consequences of Er doping, in particular, stiffening of TO1 soft mode of KTaO3. We provide information about energy level structures controlling f - f optical transitions in Er3+, on formation of minor cubic octahedral and major orthorhombic Er3+ centers. It is revealed that the temperature shift of narrow zero-phonon emission lines is strikingly unusual being much larger than that typical for trivalent rare-earth impurities.

Abstract In KTaO_3:Er crystals, we observed a temperature shift, unusual for rare earth impurities, for narrow zero-phonon luminescence lines, due to the ^4 S _3/2 → ^4 I _13/2, ^4 F _9/2 → ^4 I _15/2, and ^4 S _3/2 → ^4 I _15/2 transitions in Er^3+ impurity ions. The magnitude of the shifts turned out to be comparable with the large shifts of the R lines of the Cr^3+ luminescence in SrTiO_3:Cr and KTaO_3:Cr crystals, that is, substantially larger than that for the three-charged rare earth ions usually observed in the   f – f   luminescence spectra in ionic crystals.

In KTaO3:Er crystals, we observed a temperature shift, unusual for rare earth impurities, for narrow zero-phonon luminescence lines, due to the 4S3/2 → 4I13/2, 4F9/2 → 4I15/2, and 4S3/2 → 4I15/2 transitions in Er3+ impurity ions. The magnitude of the shifts turned out to be comparable with the large shifts of the R lines of the Cr3+ luminescence in SrTiO3:Cr and KTaO3:Cr crystals, that is, substantially larger than that for the three-charged rare earth ions usually observed in the  f–f  luminescence spectra in ionic crystals.

Photoluminescence spectra have been investigated in erbium doped GaLaS(O) glasses. The samples demonstrate intense green emission bands centered at around 525 and 550 nm due to up-conversion processes in erbium ions. The theoretical description of up-conversion intensity as a function of excitation intensity has been offered. It is based on a solution of a system of rate equations taking into account three up-conversion transitions.

Исследованы спектры поглощения ионов Er3+, внедренных в матрицу AlN. Примесь эрбия вводилась в объемные кристаллы AlN диффузией. В спектральном диапазоне 370-700 nm наблюдались линии поглощения, связанные с внутриконфигурационными электронными f-f-переходами из основного 4I15/2-состояния на уровни возбужденных состояний ионов Er3+. При температуре T=2 K детально исследованы переходы на уровни состояний 4F9/2, 2H11/2, 4F7/2, 4F5/2, 2H9/2 и 4G11/2. Количество наблюдавшихся линий для указанных переходов полностью совпадает с теоретически возможным для электронных f-f-переходов в ионах Er3+, находящихся в кристаллическом поле с симметрией ниже кубической. Узость наблюдавшихся линий и их число убедительно свидетельствуют о замещении ионами эрбия преимущественно одной регулярной кристаллической позиции. Наиболее вероятным представляется внедрение Er3+ в позицию Al3+ с локальной симметрией C3v. Определены энергетические положения уровней возбужденных состояний для исследованных переходов. Построена схема уровней энергии ионов Er3+ в кристаллах AlN. DOI: 10.21883/FTT.2017.12.45236.175

The absorption spectra of the Er3+ ions embedded in the AlN matrix have been investigated. The admixture of erbium was introduced in bulk AlN crystals by diffusion. The absorption lines, which are associated with the intraconfigurational electronic f–f-transitions from the ground 4 I 15/2-state to the levels of ion Er3+ excited states have been observed in the spectral range of 370–700 nm. The transitions to the state levels 4 F 9/2, 2 H 11/2, 4 F 7/2, 4 F 5/2, 2 H 9/2, and 4 G 11/2 have been investigated in detail at the temperature T = 2 K. The number of the observed lines for these transitions coincides with the theoretically possible one for the electronic f–f-transitions in the ions Er3+, which are in the crystal field with the symmetry below cubic. The narrowness of the observed lines and their number convincingly testify the replacement of preferably one regular crystalline position by erbium ions. The implementation of Er3+ in the Al3+ position with the local symmetry C 3v appears the most probable. The energy positions of the levels of excited states for the investigated transitions have been determined. The diagram of the Er3+ ion energy levels in the AlN crystals has been built.

This Letter presents results of analysis of the absorption spectra of AlN:Er3+ bulk crystals. In the spectral of 370–700 nm, absorption lines responsible for intraconfiguration electron transition from the ground state 4I15/2 to the excited states of Er3+ ions are found. Transitions to the levels of the 4F9/2, 2H11/2, and 4G11/2 states at 2 K are studied in detail. The number of observed lines for these transitions fully agrees with that theoretically possible for f–f electron transitions in Er3+ ions found in a noncubic crystal field. The small width of the observed lines and their number indicate that erbium ions displace mostly one regular crystal position. Most probably, Er3+ occupies the position of Al. Energy positions of excited states for the considered transitions are determined.

The f–f absorption and emission spectra of Er3+ impurities were observed and identified in KTaO3 and K1 – x Li x TaO3 single crystals. It was shown that Li off-centers related random fields markedly influence intensity, width and position of zero-phonon lines. The detail analysis of the absorption spectra obtained allowed one to determine energies of the Stark sublevels of excited states for Er3+ dominant centers of noncubic symmetry.

Results of a detailed study of optical absorption and photoluminescence of slightly erbium-doped (~50ppm) strontium titanate (SrTiO3) single crystals are presented. This study allowed us to specify the structure of energy levels that determine the main internal optical transitions within the 4f11 electron configuration of Er3+ ions in SrTiO3:Er crystals at temperatures below the transition from cubic to tetragonal phase. The numbers of energy levels of the studied multiplets obtained at 2K correspond exactly to the theoretically expected numbers of crystal field levels for multiplets of only one type of Er3+ centers with non-cubic symmetry. Experimental results indicate that Er3+ ions most probably substitute for Sr2+ ions acting in SrTiO3 as ionized donors. Such location of Er3+ ions is consistent with both n-type conductivity and substantial free charge carrier absorption in the infrared spectral region observed in the studied SrTiO3:Er single crystals at room temperature.

We report on optical absorption and EPR spectroscopy studies of low Er doped (50 ppm) SrTiO3 single crystals. In the region of 400–650 nm a set of optical intra‐configurational f–f transitions from the 4I15/2 ground state to the excited 4F9/2, 4S3/2, 2H11/2, and 2H9/2 Stark sublevels of the Er3+ impurity ions were observed and identified. At T = 2 K the number of registered optical transitions evidences the presence of only one type of Er3+ centers with non‐cubic symmetry. The system of the energy levels for Er3+ excited states is determined. The X‐band EPR spectra at 5.2 K revealed the rhombic symmetry of Er3+ impurity centers. The components of a rhombic g‐tensor were defined. It was suggested that Er ions substitute Sr ions in A‐sublattice sites.

The YAlO 3 : Tm 3+ single crystal has been studied on a wide-band EPR spectrometer. The EPR spectra of Tm 3+ ions in the frequency range of 90–160 GHz have been detected for the first time. It has been confirmed that thulium ions substitute the position of Y 3+ in the crystal lattice. The detected spectra have been described with the use of a spin Hamiltonian with the effective spin S = 1/2. A comparative analysis of the orientation of the magnetic axes of the Tm 3+ paramagnetic center with earlier data on other rare-earth ions has been performed.

The optical absorption spectra of Li6Y(BO3)(3):Er3+ crystals have been studied. The absorption lines corresponding to intraconfiguration electronic transitions from the I-4(15/2) ground state to the levels of excited states of Er3+ ions have been found in the spectral range of 370-700 nm. The transitions to the F-4(9/2), S-4(3/2), H-2(11/2), F-4(7/2), F-4(5/2), F-4(3/2), H-2(9/2), and (4)G(11/2) levels have been investigated in detail at 2 K. The number of lines observed for these transitions corresponds to the theoretical maximum for the f-f electronic transitions in Er3+ ions located in the noncubic crystal field. The narrowness of the lines observed and their number indicate that erbium occupies one regular position (specifically, the yttrium position). The energy levels of the excited states have been determined for the transitions under study.

Infrared reflection and ESR spectra of KTaO 3 : Er 3+ single crystals have been investigated. The frequency of the lowest optical phonon mode TO 1 has been found to increase as compared to undoped KTaO 3 crystals, which indicates the suppression of the ferroelectric instability of the system. The ESR spectra have revealed the presence of two Er 3+ centers of different (cubic and non-cubic) symmetries in KTaO 3 : Er 3+ .

We report the results of a multifaceted study of optical and dielectric properties of erbium-doped (500?ppm) potassium tantalate incipient ferroelectric single crystals. Studies of optical absorption and photoluminescence spectra allowed us to determine the system of energy levels that control the main internal optical transitions in the 4f electronic shell of Er3+ in KTaO3. It was found that at least two types of Er3+ centres, major and minor ones, are present. The major centres are non-cubic, formed by Er3+ substituting for K+ sites; these are responsible for the n-type conductivity of KTaO3:Er crystals. Wideband optical absorption with a maximum at 1.13?eV (??=?1097?nm) was observed in the near-IR range and was attributed to polaron formation. Low-temperature far-infrared reflectivity studies revealed an increase in the frequency of the lowest transverse optical mode and a decrease in the dielectric permittivity in comparison with undoped KTaO3 crystals. This stiffening means the suppression of the ferroelectric instability in the system. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The first results of the study of optical absorption spectra of KTaO3: Er3+ crystals are presented. In the 350–660-nm region, lines are observed deriving from intraconfigurational electronic transitions from the 4 I 15/2 ground state to levels of the 4 F 9/2, 4 S 3/2, 2 H 11/2, 4 F 7/2, 4 F 5/2(4 F 3/2), 2 G 9/2, and 4 G 11/2 excited states of the Er3+ ions. A comprehensive study of transitions to the 4 F 9/2, 4 S 3/2, 2 H 11/2, and 4 F 7/2 levels at 77 K is carried out. The number of lines observed for the above transitions fits the theoretically possible number for ƒ-ƒ electronic transitions in Er3+ ions in the cubic crystal field. In the case of a differently charged substituted ion, this situation occurs only under nonlocal impurity charge compensation. The energies of the excited state levels for the transitions under study are determined.