Optical Materials: X最新文献

Two series of rare earth coordination compounds have been synthesized (Na[RE(L₄)] (labeled as 1RE) and PPh₄[RE(L₄)] (labeled as 2RE), where RE = Y³⁺, Eu³⁺, Tb³⁺, L = 2,2,2-trichloro-N-(diphenylphosphoryl)acetamide) to determine the possibility of modifying their photophysical and magnetical properties by changing the counterion. The crystal structure of 1RE was determined based on the single-crystal X-ray diffraction and the crystal structure of 2RE was determined based on quantum chemistry computational procedures. Characterization of the physicochemical properties of the compounds was carried out using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), ¹H and ³¹P NMR spectroscopy as well as FT-IR, absorption and luminescence spectroscopy in the temperature range of 300 - 77 K. The rate constants of radiative (A_rad) and non-radiative (A_nrad) transitions, intrinsic ($Q_{\mathrm{Ln}}^{\mathrm{Ln}}$) and overall ($Q_{Ln}^L$) emission quantum yields, sensitization efficiency (η_sens), the experimental and theoretical intensity parameters (Ω_λ), the forward ($W^S$, $W^T$) and backward ($W_b^S$, $W_b^T$) intramolecular energy transfer (IET) rates were determined. Magnetic properties of Tb³⁺ compounds were studied in a constant field of 0.5 T in the temperature range of 1.8–300 K. Dynamic AC magnetic susceptibility measurements were carried out as a function of temperature and frequency for 1Tb and 2Tb. Only in the case of 2Tb, in the presence of an external DC field, a slight temperature dependence of in-phase χ′ and out-of-phase χ'' susceptibility was recorded. Based on experimental and theoretical results, the significant effect of counterion on the photophysical and magnetic properties of RE chelates has been demonstrated and clarified, providing valuable guidance for the design of bifunctional electromagnetic radiation converters.

The paper presents thermoluminescence (TL) studies that aim to establish the possibility of using such analysis to determine the date of the construction, transformation and/or rebuilding of a historical church. The determination of the age of building structures using the form of absolute dating that is now used by architects and archeologists is difficult and complex. A relatively large error of estimation can be observed in archeological studies. In the case of samples from the Middle Ages, such errors are not acceptable. The authors attempted to develop an alternative spectroscopic TL method for such studies, and proposed that the composition of bricks should be measured using X-ray diffraction, electron microscopy (EM) and TL spectra. The bricks for the testing were taken from internal walls and the walls in the attics of churches, i.e. from places built during the last stage of construction works. The TL measurements were made using x-ray and β source excitation within the temperature range of 25–500°C. Two different sizes of grains were studied: small (∼0.1 mm) and large (∼0.5 mm). A gothic church in Świebodzin from 1555, which has a well-known history of its construction, was selected for the investigations. Due to the fact that this church is 326 years younger than the two churches evaluated and described in [1], the composition of its bricks could be different. Therefore, the authors decided to compare the XRD data, EM results and TL spectra for bricks taken from all three churches. The intensities of the TL and the integrated TL intensities were determined. The measurement results are important for creating a relationship between the TL intensity and the date a building object was constructed. Moreover, thanks to this it was possible to verify the construction date of Saski Palace in Warsaw.

High-quality Cs₃Cu₂I₅:In single crystals with a 7 mm diameter were grown by using the vertical Bridgman method. These crystals have a high optical transmittance (>75 %) and emit a bright red-orange light under both UV and X-ray irradiation. The Cs₃Cu₂I₅:In crystals can exhibit a high photoluminescence quantum efficiency (PLQY) of 79.5 %, thus we explored the potential applications for light-emitting diodes (LED). The fabricated LED demonstrated CIE color coordinates of (0.553, 0.431) with a color rendering index (Ra) of 77, making it suitable for supplementary light in plant growth. Moreover, we evaluated their gamma-ray spectroscopy capability by using an avalanche photodiode (APD) detector. Under ¹³⁷Cs gamma-ray irradiation, the gamma scintillation yield and energy resolution gradually degraded as the In concentration increased, which can be attributed to an enhanced afterglow after In doping.

Transition metal ions with a 3d³ electronic configuration are among the most prevalent dopants in luminescent materials, favored for their distinctive energy level configurations and the ability to tailor their spectroscopic properties by modulating the crystal field strength. Despite a history of applications spanning over six decades, recent years have seen a surge in increasingly sophisticated and innovative applications that warrant particular attention. Consequently, this paper will provide a comprehensive overview of the potential uses of phosphors ion-doped with a 3d³ electronic configuration in advanced applications including: laser, lighting, NIR vision, plant cultivation, temperature and pressure sensing, optical heating, fingerprint detection, optical power meters.

A comparative analysis of praseodymium (Pr³⁺)-doped fluoride glasses, APLF [20Al(PO₃)₃–80LiF–PrF₃], BCAYF (19BaF₂–33.25CaF₂–42.75AlF₃–5YF₃–PrF₃), and BCAPLF (19BaF₂–33.25CaF₂–42.75AlF₃–15P₂O₅–20LiF–PrF₃), reveals the effect of the host matrix on the optical properties, particularly the luminescence behavior of Pr³⁺ ions. X-ray absorption near edge structure (XANES) spectroscopy verifies the presence of Pr ions in the glasses with a +3 oxidation state. Absorption spectra results suggest that the lowest energy level of the Pr³⁺ 4f5d configuration is influenced by the oxide/fluoride ratio of the glasses. As both interconfigurational 4f5d and intraconfigurational 4f² transitions are observed, the energy gap between the lowest level of the 4f5d configuration and the overlapping ¹S₀ level of the 4f² configuration is found to influence the predominance of UV emissions from the 4f5d and ¹S₀ levels as well as their decay times. Consequently, a larger 4f5d-¹S₀ energy gap of ∼5000 cm⁻¹ leads to a more intense UV emission from the 4f5d level with a faster decay time. These results underscore the significance of minimizing the energy of the 4f5d level and increasing the gap between 4f5d-¹S₀ levels to be able to obtain fast UV emissions from Pr³⁺-doped fluoride glasses.

Ongoing efforts to develop a predictive model governing the host-referred binding energies (HRBEs) and vacuum-referred binding energies (VRBEs) of transition metal dopants in inorganic host compounds are stymied by a lack of cross-compound data sets that capture transitions between the dopant ions and the valence and conduction bands of the hosts. Herein, we have compiled data consistent with Mn²⁺ charge transfer processes in 53 different compounds, spanning fluorides, oxides, chlorides, bromides, and nitrides. By assigning these transitions to Mn²⁺ → conduction band metal-to-metal charge transfer and combining these energies with the binding energies of electrons in the valence and conduction bands of the various hosts, we have calculated the HRBEs and VRBEs of the Mn²⁺ ion across a range of compounds. We show that variations in the Mn²⁺ VRBE are small relative to the variations in the VRBE of the valence and conduction bands, which manifests an approximately linear relationship between the Mn²⁺ HRBE and the bandgap energy of host compounds. We investigated the relationship between the Mn²⁺ VRBE and the various structures of the host compounds and showed that the chemical shift experienced by the Mn²⁺ ion depends on the electronegativity of the ligand, the Mn²⁺ coordination, and the Mn-ligand bond lengths in a predictable manner.

In this work, we reported the results of photoluminescent and structural investigations of Gd³⁺/Tb³⁺ co-doped silicate xerogels as well as derivative SiO₂-LaF₃ nano-glass-ceramics. The molar ratio of appropriate acetates used during the synthesis, i.e., La(AcO)₃:Gd(AcO)₃:Tb(AcO)₃ was fixed to x:(0.95-x):0.05. Based on XRD measurements, the crystallization of hexagonal LaF₃ nanophase was verified without any admixture of GdF₃ phase, even for samples with La³⁺:Gd³⁺ molar ratio ≤1. The optical characterization of fabricated Gd³⁺/Tb³⁺ co-doped sol-gel materials involved the registration and analysis of photoluminescence excitation (PLE) and emission spectra (PL), as well as the decay curves for the ⁶P_7/2 (Gd³⁺) and the ⁵D₄ (Tb³⁺) excited levels. Upon excitation at λ_ex = 275 nm wavelength, the fabricated sol-gel samples revealed the series of emission lines assigned to the electronic transitions from both dopants, i.e., Gd³⁺ and Tb³⁺, indicating apparently the occurrence of Gd³⁺/Tb³⁺ energy transfer process (ET). The photoluminescence measurements comprehensibly proved the competitiveness between Gd³⁺ and Tb³⁺ ions to be entered into LaF₃ fluoride nanocrystal lattice, formed during annealing of as-prepared xerogels. Based on the recorded PL spectra for fabricated sol-gel samples, some chromatic parameters were calculated, i.e., chromaticity coordinates (CIE), correlated color temperatures (CCT), and color purities (CP). The prepared Gd³⁺,Tb³⁺ co-doped samples are able to emit green light with CCT values in a range from 5967 K to 6291 K, and high CP reached 70 %, which predispose them for use as efficient constituents for developing green-emitting devices.

Far-red (FR) photosensitive pigment (P_FR) is vital for plant photomorphogenesis. Phosphor-converted (pc) LEDs are the next-generation FR light devices. How to obtain FR-emitting phosphors with a good quantum efficiency, suitable photoluminescence and high thermal stability is still difficult. Herein, we optimize the Y₃Ga₅O₁₂:Cr³⁺ FR phosphor, which has an emission peak at 711 nm and a full width at half maximum of 74 nm, closing to the P_FR absorption band. By adopting the solid-state sintering technology, the internal quantum efficiency reaches 85.5 %, more than 1.5 times higher than that reported by the liquid reaction (55 %). Furthermore, the external quantum efficiency reaches as high as 33.1 %, indicating the promising application in FR-LEDs.

Thermoluminescence (TL) often involves the liberation of a charge carrier (an electron or a hole) from a charge carrier trapping centre into the conduction band (CB) or the valence band (VB) with subsequent recombination with a counter charge carrier at a luminescence centre. TL glow peak analysis can provide the energy $\Delta E_t$ needed to liberate such charge carrier which then defines the location of the charge transition levels (CTL) of the carrier trapping centres below the CB-bottom or above the VB-top. The temperature at the maximum of the TL glow peak changes 3–4 K per 0.01 eV change in $\Delta E_t$ thus providing an extremely sensitive probe of energy changes in CTLs. This work collects and reviews data on glow peaks due to electron or hole release from lanthanide dopants in 36 different inorganic compounds. To compare results from different literature sources, data were always re-analysed using the same method that is solely based on the temperature at the maximum of the glow peak. The changes in $\Delta E_t$ along the lanthanides series provides insight at the sub 0.1 eV level on the changes in CTL energies. We will use a compound-dependent parameter to account for the nephelauxetic effect and a compound dependent parameter to account for lattice relaxation around the lanthanide. Together with information from lanthanide luminescence spectroscopy, the vacuum referred binding energy (VRBE) diagram will be constructed for each compound. The lanthanide electron or hole trap depth read from the VRBE scheme will be compared with that derived from the TL glow peak. Surprisingly good agreement will be demonstrated.

Thermal management poses a significant challenge for conventional phosphor-converted white LEDs (pc-WLEDs), thereby affecting their overall efficiency. Single crystal phosphors (SCPs), such as Y₃Al₅O₁₂:Ce (YAG:Ce), exhibit enhanced efficiency and thermal stability in comparison to conventional powder phosphors. The garnet Lu₃Al₅O₁₂:Ce (LuAG) has been characterized as a green phosphor with even higher than YAG:Ce temperature stability, making it suitable for use in high-power WLEDs. However, there are some difficulties in obtaining suitable components with longer emission wavelengths in LuAG:Ce phosphors. As a way to solve this issue, the article suggests the growth of LuAG:Ce single crystalline films onto YAG:Ce substrates, thereby producing a composite color converter that possesses adjustable parameters. This paper presents a comprehensive analysis of the fabrication process as well as the characteristics of a two-layered LuAG:Ce film/YAG:Ce substrate composite color converter. The results of investigations of the structural, luminescence and photoconversion characteristics of composite color converters were presented as well. This study includes also consideration of the effect of varying LuAG:Ce film thicknesses and concentrations of Ce³⁺ in YAG:Ce substrates on photoconversion characteristics of composite converters.