Excitation Of Charge-transfer Band Research Articles

A brief review of characteristic luminescence properties of Eu3+ in mixed-anion compounds.

Trivalent europium (Eu3+) ions show red luminescence with sharp spectral lines owing to the intraconfigurational 4f-4f transitions. Because of their characteristic luminescence properties, various Eu3+-doped inorganic compounds have been developed to meet the demands of optoelectronic devices. Regardless of shielding by the outer 5s and 5p orbitals, the properties of the Eu3+:4f-4f transition depend on the local environment, such as the shapes of the coordination polyhedra, site symmetry, nephelauxetic effects, crystal field effects, and bonding character. Mixed-anion coordination, where multiple types of anions surround a single Eu3+ ion, can directly affect the optical properties of Eu3+. We review the luminescence properties of Eu3+ ions in mixed-anion compounds of the oxynitride YSiO2N and oxyhalides YOX (X = Cl or Br). Oxynitride and oxyhalide coordination results in characteristic transition probabilities and branching ratios of the 5D0 → 7F0-6 transitions due to distorted structural environments and red-shifted charge transfer excitation bands due to an upward shift of the valence band. The expected and experimentally observed features of Eu3+ luminescence in mixed-anion compounds are outlined based on band and Judd-Ofelt theories. Future applications of the intense red luminescence at ∼620 nm under near-ultraviolet light illumination in Eu3+-doped mixed-anion compounds are introduced, and material design guidelines for new functional Eu3+-doped phosphors are presented.

High-quality reddish-orange-emitting Sr6Y2Al4O15:Eu3+ phosphors for solid-state lighting and anti-counterfeiting applications

The reddish-orange emitting Sr6Y2Al4O15:Eu3+ phosphors were synthesized via a high-temperature solid-state reaction technique, and their luminescent properties were systematically studied. The dominant emission peak assigned to the electric dipole transition (5D0 → 7F2) was recorded at 612 nm owing to the non-inversion symmetry of the substituted sites of Eu3+ ions under the excitation of charge transfer band (∼261 nm). The emission of Sr6Y2Al4O15:Eu3+ revealed a Commission Internationale de l'Eclairage (CIE) chromaticity coordinate of (0.571, 0.368) and a color purity of 93.6 %. The thermal stability and photoluminescence quantum yield (PLQY) of Sr6Y2Al4O15: Eu3+ were analyzed, exhibiting a high thermal stability of 88.24 % at 423K and a good external PLQY of 36.24 %. Furthermore, the solid-state lighting (SSL) and flexible anti-counterfeiting applications of Sr6Y2Al4O15:Eu3+ were demonstrated. The red light-emitting diode (LED) was packaged with ∼260 nm ultraviolet LED chip, representing a CIE chromaticity coordinate of (0.5955, 0.3592) and a color purity of 86.53 %. The flexible anti-counterfeiting film was fabricated with polydimethylsiloxane polymer, and it showed tunable emission under different excitations. Moreover, the anti-counterfeiting ink was prepared and printed on various substrates. Consequently, the reddish-orange emitting Sr6Y2Al4O15: Eu3+ phosphors with high color purity, good thermal stability, and high quantum efficiency were introduced and potentially used in SSL and flexible anti-counterfeiting applications.

Ingredient regulation engineering of samarium(III)-activated double-perovskite niobate matrices

By adjusting the chemical compositions of A and B sites, single Sm3+-activated double-perovskite A2BNbO6 (A = Ca, Sr, and Ba; B = Y and In) phosphors were prepared. Their phase structure and perovskite structure distortion were analyzed. Interestingly, the Ca2YNbO6:Sm3+ phosphors exhibited the strongest emission intensity. After regulating Ca to Sr and Ba compositions, the redshift in the photoluminescence emission spectrum was observed under the charge transfer band excitation. Note that all the obtained samples presented beneficial thermal stability (>62 % at 423 K). Particularly, the Ca2InNbO6:Sm3+ phosphors displayed the highest thermal stability (93.20 % at 423 K). Besides, the luminescence characteristics such as color purity, chromaticity coordinates, luminescence decay curve, etc. were systematically analyzed. This work can provide a valuable database for researchers to find suitable Sm3+-activated double-perovskite frameworks by regulating suitable ingredients.

Structural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate

AbstractStructural and optical properties of Mg1−xMnxP2O6(x = 0–1.0) magnesium metaphosphate were investigated in detail. The complete solid solution of MgP2O6–MnP2O6is confirmed as monoclinic space groupC2/c. The dynamic luminescence was studied by changing the Mn2+content (0–100 mol%) and temperature (10–300 K). There is a good chemical homogeneity in Mg1−xMnxP2O6(x = 0–1.0), which can be supported by the linearly varying cell size and the gradually changing vibration spectrum. However, the optical properties of the solid solution do not show a continuous change trend, that is, an obvious inflection point appeared whenx = 0.5. Mg1−xMnxP2O6(x = 0.1–0.5) shows a dominant O2− → Mn2+charge transfer (CT) absorption in the near UV region and feeble d–d transitions of Mn2+in visible wavelength region. However, Mg1−xMnxP2O6(x = 0.6–1.0) presents a strong d–d absorption transition and nearly disappeared CT band. The changing trend of optical absorption is also maintained in the excitation and emission of the solid solutions. In Mg1−xMnxP2O6(x = 0.1–0.5), (Mn, Mg)O6octahedron has slight distortion, and the effective luminescence only occurs when CT band excitation is used. In contrast, in Mg1−xMnxP2O6(x = 0.6–1.0), (Mn, Mg)O6octahedron is highly distorted, and only excitation at d–d transition produces effective luminescence. This research highlights the critical role of MnO6octahedral distortions in the luminescence properties of Mn2+activators. The research provides a reference for developing optical materials.

Charge transfer band excited (Sr,Ba)2YTaO6:Eu3+ reddish-orange-emitting phosphors for luminescence lifetime thermometry and flexible anti-counterfeiting labels

Strong reddish-orange-emitting (Sr,Ba)2YTaO6:Eu3+ phosphors were synthesized via a facile solid-state reaction. Due to the occupation of Y3+ ions in the high symmetry (Oh) sites as an inversion symmetry site, the 5D0 → 7F1 magnetic dipole transition peak was dominant in the (Sr,Ba)2YTaO6:Eu3+ phosphors under the charge transfer band excitation. Both Sr2YTaO6:Eu3+ (SYTO:Eu3+) and Ba2YTaO6:Eu3+ (BYTO:Eu3+) phosphors exhibited good thermal stability and quantum yield. Their luminescence sensing performances (relative sensing sensitivity) were determined to be 0.18% K−1 (BYTO:0.1Eu3+) and 0.13% K−1 (SYTO:0.1Eu3+) with the aid of the Struck and Fonger models. Furthermore, novel deep ultraviolet-excited phosphors-based polydimethylsiloxane flexible light-emitting films were fabricated for anti-counterfeiting applications. Consequently, this work reveals that the strong reddish-orange-emitting (Sr,Ba)2YTaO6:Eu3+ phosphors are suitable for dual-functional applications including luminescence lifetime thermometry and flexible anti-counterfeiting labels.

Realizing dual-mode luminescent thermometry with excellent sensing sensitivity in single-phase samarium (III)-doped antimonite phosphors

In this work, we synthesized the Sr 2 InSbO 6 (SISO) phosphors with good temperature sensing performances for luminescent thermometry. Both X-ray diffraction and Rietveld refinement results verified that SISO: Sm 3+ phosphors have a monoclinic structure with the P2 1 /n space group. Under the charge transfer band excitation, three dominating emission peaks which are attributed to the f-f transition of Sm 3+ ions from the 4 G 5/2 excited level to the 6 H 5/2 , 6 H 7/2 , and 6 H 9/2 levels, respectively were observed. As the main concentration quenching mechanism was controlled by dipole-dipole (d-d) interaction, the optimum doping concentration in SISO:Sm 3+ phosphors was found to be 3%. With the aid of the temperature-dependent fluorescence intensity and lifetime, the maximum relative temperature sensitivities, S R1 and S R2 , of SISO:0.03Sm 3+ phosphor were 10.9% K −1 and 2.15% K −1 at 523 K, respectively. On the account of these results, single-phase Sr 2 InSbO 6 :Sm 3+ phosphors with remarkable temperature sensing performances can be applied in dual-mode optical thermometers. • Sm 3+ -activated Sr 2 InSbO 6 phosphors were firstly synthesized. • The crystal structure and photoluminescence properties were investigated. • The concentration quenching mechanism was identified in detail. • The sensing sensitivity was 10.9% K −1 based on the fluorescence intensity ratio. • The sensing sensitivity was 2.15% K −1 based on temperature-dependent lifetime.

Observation of up conversion/ down conversion luminescence and structural analysis of La2Zr2O7: Pr3+ nano phosphors

Charge transfer band (CTB) transition significantly improves the photoluminescence properties of phosphor materials due to its higher absorption efficiency than the characteristic excitations of rare-earth ions. La2Zr2O7 (LZO): Pr3+ phosphors with varying doping concentrations of Pr3+ were synthesized through the hydrothermal method. The formation of the pure pyrochlore phase was confirmed from powder X-ray diffraction (XRD). The structural analysis was performed from Rietveld refinement of the XRD data. Field emission electron microscope (FESM) equipped with EDX spectroscopy was used to study the surface morphology and elemental compositions. X-ray photoelectron spectroscopy (XPS) analysis of the optimized sample provides the bonding state of the compositions. Under 257 nm CTB excitation, the photoluminescence emission spectra (PL) exhibit all the characteristic emission peaks of Pr3+ ion. The transitions involved in the excitation and emission process have been shown in the energy level diagram of Pr3+ ions. The Concentration quenching effect was explained from Bless relation and Dexter energy transfer theory between activator ions. Decay curves of the prepared phosphors show bi-exponential behavior. The up-conversion emission spectra were recorded under 980 nm laser excitation. The optical transition in the UV–Vis range was investigated based on the diffuse reflectance spectra, and the results match well with the excitation spectra. The photometric study informs the color and the quality of the emitted light. The outcomes produce a new synthesis method to prepare La2Zr2O7:Pr3+ nano phosphor that can be an excellent candidate for solid-state lighting and UV/NIR to the visible converter in solar cell applications.

Charge transfer band excitation of La3NbO7:Sm3+ phosphors induced abnormal thermal quenching toward high‐sensitivity thermometers

AbstractDifferent luminescent behaviors of La3NbO7:Sm3+ phosphors under the excitations of charge transfer band (CTB, 250 nm) and featured absorption peak (6H5/2 → 4H7/2, 405 nm) of Sm3+ ions were demonstrated. Under the excitation wavelength of 405 nm, the optimal La3NbO7:0.1Sm3+ phosphor exhibited an orange‐red emission while the chromatic coordinate was found to be (0.609, 0.387), which also showed the excellent thermal performance, exhibiting its emission intensity of about 90.67% at 423 K with respect to 303 K. In the case of CTB excitation, the La3NbO7:0.1Sm3+ phosphor emitted an orange‐yellow region with the chromaticity coordinate of (0.540, 0.443), and the emission intensity was stronger than the above one (λex =405 nm) even though the optimized sample would be changed to the La3NbO7:0.05Sm3+ phosphor. With the increase of temperature, the obtained sample revealed an abnormal thermal quenching phenomenon between the emission peak of the host material and the emission transition of 4G5/2 → 6H9/2 under the excitation wavelength of 250 nm, which could be suggested to turn into a pair of thermal‐couple levels. Therefore, the sensing sensitivity of the obtained sample was further investigated based on the fluorescence intensity ratio theory. Eventually, the absolute and relative sensing sensitivities of the La3NbO7:0.01Sm3+ phosphor were estimated to be as high as 5.379 × 10−2 K−1 and 1.60% K−1, respectively.

Development of Eu3+-doped phosphate glass for red luminescent solid-state optical devices

Eu3+-doped lithium phosphate glasses, (63-x) P2O5–32Li2O–5Al2O3‒xEu2O3, where 0≤x≤5 mol% concentrations were prepared by conventional melt-quenching technique. The glasses were characterized through various physical and optical properties at room and low temperatures (10K). The radiative transition probability, stimulated emission cross-section, branching ratio and radiative lifetime of the glasses were evaluated following the Judd-Ofelt theory. Two-fold increase in the photoluminescence (PL) intensity was observed under 394 nm excitation at 10K as compared to that measured at room temperature. The absence of 7F1→5D3,1 excitation transition at 10K was found due to a decrease in thermal energy of ground states. The presence of O2−−Eu3+ charge transfer excitation band (CTB, 200–275 nm) was observed. An optimum PL emission was recorded in the glass with 3 mol%, whereas the concentration quenching was noticed for the sample with 5 mol%. The results show that the Eu3+-doped lithium phosphate glasses could be potential candidates for red laser applications.

Structure variation and luminescence enhancement of BaLaMg(Sb, Nb)O6:Eu3+ double perovskite red phosphors based on composition modulation

A series of BaLaMgSb1-xNbxO6:Eu3+ double perovskite red phosphors was successfully obtained. X-ray diffraction ans Rietveld refinement analyses were conducted to determine the phase information and the detailed structure parameters. The coordinate variations of both La3+/Eu3+ and Sb5+/Nb5+ were discussed to elucidate the influence of B-site ion doping on the lattice variation. Luminescence properties, excitation and emission spectra, were presented to show the advantages of doping with Nb5+ ion. Ultraviolet-vis diffuse reflectance spectra were performed to reveal the reason for the decreased emission intensity under the charge transfer band excitation. Moreover, band gap energy was estimated to clarify the relationship between the increased intensity (λex = 395 and 465 nm) and Nb5+ concentration. Intensity ratios of I(615)/I(590) were performed to show the symmetry variation of the lattice. Thermal quenching property was also investigated and the quenching mechanism was discussed in detail based on the ionization process.

Effects of Al3+ substitution on the luminescence properties of LuNbO4 doped with Eu3+ and Tb3+ ions

The effect of Al3+ substitution on the enhancement of the luminescence of Lu1–xAlxNbO4:Eu3+ and Lu1–xAlxNbO4:Tb3+ was investigated. X-ray diffraction patterns confirmed that the Eu3+, Tb3+, and Al3+ ions were fully incorporated into the Lu3+ sites. In the case of Lu1–xAlxNbO4:Eu3+, the predominant red emission (614 nm) was assigned to the 5D0 → 7F2 transition of Eu3+ and for x = 0–0.05, its intensity increased up to ~125 and 108% under 395 nm (7F0 → 5L6) and a charge transfer band excitation, respectively. For Lu1–xAlxNbO4:Tb3+, the strongest emission band peaking at 551 nm was attained in the green region among multiple emission bands corresponding to the 5D4 → 7FJ transitions of Tb3+. Increasing the x values from 0 to 0.05 increased the green emission significantly by ~137%. These phenomena were explained by the local structural distortions and crystal field asymmetry surrounding Eu3+ and Tb3+, which were attributed to a large difference in the ionic radii of Al3+ and Lu3+.

Synthesis and luminescence properties of Eu3+ and Dy3+ ions single and co-doped Ba2LaV3O11 phosphors for white-light applications

We report the synthesis and luminescence properties of the rare-earth ions doped Ba2LaV3O11 phosphors. The Dy3+ and Eu3+ ions single doped and Dy3+/Eu3+ ions co-doped Ba2LaV3O11 phosphors were synthesized via a citrate-based sol-gel method. The surface morphology, phase purity, photoluminescence properties and thermal stability of the synthesized phosphors were determined from the X-ray diffractometer, field-emission scanning electron microscope and spectrofluorometer, respectively. The obtained results indicate that the prepared phosphor material was crystallized in monoclinic phase with the space group P21/c (14) and the diffraction peaks were well matched with the standard JCPDS (#40-0105) card values. Under charge transfer band excitation wavelengths, the Eu3+ (277 nm) and Dy3+ (274 nm) single doped phosphor samples exhibited characteristic red and yellow emissions, respectively. Meanwhile, the Dy3+/Eu3+ co-doped phosphor samples showed near white-light emission.

Yb3+ concentration influences UV–Vis to NIR energy conversion in nanostructured Pr3+ and Yb3+ co-doped SiO2-Nb2O5 materials for photonics

We describe the synthesis of Pr3+/Yb3+ co-doped and Pr3+-doped SiO2-Nb2O5 nanocomposites; we also investigate energy transfer processes between the doping ions, which involve UV–Vis to infrared energy conversion. The emission spectra in the near infrared (NIR) region, 900–1650 nm, indicated energy transfer from Pr3+ to Yb3+ upon blue excitation of the Pr3+ ions. UV charge transfer band excitation elicited efficient Yb3+ emission at about 1.0 µm. The nanocomposite co-doped with 0.5 mol% Pr3+ and 1.0 mol% Yb3+ provided maximum energy transfer efficiency. The Pr3+ ion 3P0 excited state lifetime decreased from 11.8 to 3.7 µs as the Yb3+ ion content in the Yb3+/Pr3+ co-doped nanocomposites increased from 0.25 to 1.0 mol%. This observation attests for energy transfer from Pr3+ to Yb3+ ions. On the basis of these results, Pr3+/Yb3+ co-doped SiO2-Nb2O5 nanocomposites are promising materials for UV–Vis to NIR energy conversion.

A single-phase white light emitting Pr3+ doped Ba2CaWO6 phosphor: synthesis, photoluminescence and optical properties

Pr3+ doped Ba2CaWO6 phosphor were prepared by traditional high-temperature solid-state reaction technique. The structure evolution was systematically investigated by X-ray diffraction (XRD), energy–dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The X-ray powder diffraction patterns indicate that the prepared phosphors crystallized in the cubic double-perovskite structure. The functional groups were identified using FTIR spectra and the elements present in the composition were confirmed by the EDS profile. The morphology of the phosphor was identified using SEM and TEM analysis. The PL spectra illustrated that these phosphors could be efficiently excited by charge transfer band of host and the maximum luminescence intensity was observed at 0.06 wt% of Pr3+ ion. Upon the charge transfer band excitation, emission spectra showed peaks at 489, 532, 647, 685 and 737 nm corresponding to 3P0→3H4, 3P1→3H5, 3P0→3F2, 3P0→3F3 and 3P0→3F4 transitions respectively. The concentration quenching of Ba2CaWO6:Pr3+ phosphor can be mainly attributed to dipole-dipole interaction. The CIE coordinates were estimated to be close to the white region. The decay curves are well fitted with double exponential decay models. The standard and modified Judd-Ofelt (JO) theories were used to determine the Judd-Ofelt intensity parameters, radiative transition probabilities and branching ratios. The optical properties indicate that Ba2CaWO6:Pr3+ phosphors can produce white light emission from a single phase host and its potential application for solid-state lighting and display devices.

Charge transfer transition and energy transfer in Eu3+-doped Gd10V2O20

Eu3+-doped Gd10(1-x)Eu10xV2O20 (x = 0 – 1) phosphors were synthesized via the sol-gel process. The formation of a single phase compound was verified through the X-ray diffraction studies. Luminescence properties of Gd10V2O20:Eu3+ are investigated by optical and laser excitation spectroscopy. The emission and excitation spectra, luminescence decays were measured in the temperature region 7–300K. The strong emission due to the vanadate group of Gd10V2O20:Eu3+ is observed at low temperature. The charge transfer transition of Eu3+ depends strongly on the Eu3+-concentration in Gd10V2O20:Eu3+. The emission intensity as a function of Eu3+ concentration under excitation of charge transfer band is inconsistent with that of the 4f7 states (the 5L6 state) of Eu3+. The energy transfer occurs between two Eu3+ ions at low Eu3+ concentration (< 10mol%), while energy diffusion dominates at high Eu3+ concentration.

Luminescence properties and charge transfer mechanism of host sensitized Ba2CaWO6:Eu3+ phosphor

Eu3+ ions activated Ba2CaWO6 phosphors were synthesized by the conventional high temperature solid-state reaction method. The crystalline nature of the prepared phosphor was identified through XRD analysis and Williamson-Hall plot method. The compositional analysis was carried out by means of EDS. The morphology of the obtained samples were characterized by SEM and TEM analyses. Vibrational modes were studied using FTIR and Raman spectroscopy. It was noticed from the photoluminescence spectra that charge transfer band excitation in the host at 314nm is much more prominent than the rare earth excitation wavelength at 393nm to give the dominant 595nm emission in the host matrix by the energy transfer mechanism. The change in emission intensity corresponding to varying concentration of Eu3+ was studied. The fluorescence lifetime of the samples were calculated. Optical transition intensity parameters and various radiative properties were calculated using the Judd-Ofelt theory. Photoluminescence spectra were used to estimate the CIE chromaticity co-ordinates and were observed to be in the orange-red region.

Effects of flux on the luminescence of MgGa2O4:Mn2+ phosphors

The effects of H3BO3 and MgF2 fluxes on the crystal structure and photoluminescence (PL) of MgGa2O4:Mn2+ phosphors were investigated. The PL excitation spectra of the powders consisted of intensive broad bands (∼290nm), and sharp peaks at longer wavelengths. The former could be attributed to charge transfer between the Mn2+ and O2− ions, referred to as charge transfer band (CTB), while the latter was attributed to the d–d transitions of Mn2+ ions. Under CTB excitation, the PL spectra exhibited green emission peaks at 505nm, assignable to the 4T1(4G) → 6A1(6S) transition of Mn2+ ions in tetrahedral sites. Compared to MgF2, H3BO3 was more favorable for phase formation, higher crystallinity, and particle size enlargement, thus resulting in a significant enhancement in the emission intensity. The Mn2+ concentration affected the CTB and the crystal structure; the strongest emission intensity was observed for a high Mn2+ concentration of 0.5mol%.

Evaluating NaREMgWO6 (RE = La, Gd, Y) Doubly Ordered Double Perovskites as Eu3+ Phosphor Hosts.

Three doubly ordered double perovskites NaREMgWO6 (RE = La, Gd, Y) have been synthesized via traditional solid-state methods, doped with Eu3+, and characterized to evaluate their promise as Eu3+ phosphor hosts. NaYMgWO6, a new member of the family, was found to crystallize in the P21 space group and is isostructural with NaGdMgWO6. Emissions characteristic of Eu3+ ions (5D0 → 7F4,3,2,1,0) were observed, with the most intense transition being the 5D0 → 7F2 transition near 615 nm. Substitution of Eu3+ onto a more compressed RE site in the NaY1-xEuxMgWO6 and NaGd1-xEuxMgWO6 hosts results in a blue shift of the charge-transfer excitation band and an increase in the intensity of the 5D0 → 7F2 transition compared to NaLa1-xEuxMgWO6. All of the hosts can incorporate high concentrations of Eu3+ before concentration quenching is observed. When the rare-earth ion is either Gd3+ or Y3+, good energetic overlap between the Eu3+ charge-transfer band and the absorption of the host lattice results in sensitization and energy transfer from the perovskite host lattice to the Eu3+ activator sites. These hosts display comparable if not better luminescence than Y2O3:Eu3+, a commonly used commercial standard, demonstrating their promise as red phosphors.

Fe3+ red phosphors based on lithium aluminates and an aluminum lithium oxyfluoride prepared from LiF as the Li Source

LiF was used as the Li source to prepare Fe3+ red phosphors based on lithium aluminates and an aluminum lithium oxyfluoride. LiF led to the three types of the host materials of α-LiAlO2, γ-LiAlO2 and Al4LiO6F with the different synthetic conditions. Metastable α-LiAlO2 crystallized up to 800°C under Li-rich conditions in the starting mixture (eg. LiF/Al(OH)3=3). α-LiAlO2 converted to γ-LiAlO2 above 800°C. The flux effect of the excess LiF resulted in the enhancement of the photoluminescence (PL) intensity at higher temperatures with the growth of the crystalline grains of γ-LiAlO2:Fe3+. The reaction between LiF and γ-Al2O3 at Li/Al=0.25 brought the formation of Al4LiO6F at 800°C and above. Red PL from Fe3+ was observed at ca. 740nm in γ-LiAlO2, 730nm in α-LiAlO2 and 690nm in Al4LiO6F under the irradiation of ultra-violet (UV) light. They had charge-transfer excitation bands in the UV region and weak excitation bands in the visible region due to the d-d (or ligand field) transition. The red PL in these phosphors originated in the tetrahedrally coordinated Fe3+.

Photophysics of Fe(III) complexes with fluorosalicylic acid isomers in aqueous solutions

Transient absorption spectroscopy is used to study photophysical processes of 1:1 Fe(III) complexes with all four fluorosalicylic acid isomers (Fe-FSAs) in aqueous solutions. Excited states of Fe-FSAs decay to the ground electronic state with two time constants. The faster process is interpreted as internal conversion to the vibrationally hot electronic ground state and the slower one - as a combination of vibrational cooling and solvation of the ground state. The results obtained for Fe-FSAs and other previously investigated Fe(III) salicylato compounds allow us to reveal the main cause of photochemical stability of the complexes upon charge transfer band excitation.