Optical Materials: X最新文献

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.

We report the optically stimulated luminescence (OSL) of natural alexandrite (BeAl₂O₄:Cr³⁺) from Brazil. Luminescence was stimulated using 470 nm blue, 525 nm green and 850 nm infrared light. The dose-response of the OSL is linear in all cases, a desirable feature of dosimetry applications. The influence of preheating on OSL suggests that electron traps associated with the thermoluminescence of alexandrite contribute to the OSL. Mechanisms responsible for luminescence in alexandrite have been briefly considered.

The influence of the synthesis method on both microstructure and morphological and electronic properties of CH₃NH₃PbI₃ (MAPbI₃) films prepared by different methods were investigated experimentally by Urbach energy and scanning electron microscopy (SEM) measurements, as well as computationally by Density Functional Theory (DFT) calculations.

This study was performed with samples prepared by three different methods including one step anti-solvent assisted spin coating and two-steps new approach that use a route in which in a first step a layer of the inorganic precursor (PbI₂) is deposited by conventional thermal evaporation and then in a second step the MAPbI₃ compound is formed through a reaction of the PbI₂ layer deposited in the first stage and a layer of the organic precursor methylammonium iodide (MAI) deposited by close spaced sublimation (CSS) and also by dipping in a MAI solution.

Improvement of luminescent thermometers requires not only the search for high-sensitivity thermometric outputs, but also availability of multiple thermometric parameters affording a combined and reliable response. We hereby detail for the first time the luminescence of Eu³⁺ in manganese tungstate (Eu³⁺:MnWO₄) solids obtained by coprecipitation under ultraviolet excitation and how this material provided an optical thermometric response from 77 K to 373 K via excitation and emission spectra. Processing of up to five thermometric parameters, namely bandwidths, band positions, band shifts and luminescence intensity ratios, resulted in relative thermal sensitivities as high as 1.56% K⁻¹ and temperature uncertainties between 0.01 and 2 K depending on the choice of the spectral parameter. In addition, we demonstrate that Eu³⁺:MnWO₄ also act as a qualitative colorimetric thermosensor because of progressive change of emission color to greenish-yellow to bluish-green upon heating under UV excitation. Therefore, our results show that the combination of broadband tungstate emissions with the 4f-4f narrow emissions of Eu³⁺ is an effective approach to achieve a multiparametric luminescent thermal response via emission, excitation and visual observation, which makes Eu³⁺:MnWO₄ a promising candidate for advanced thermometry applications.

The study is dedicated to investigation of the structural, luminescent and photoconversion properties of epitaxial converters based on the single crystalline films of Ce³⁺ doped Ca₃Sc₂Si₃O₁₂ (CSSG:Ce) garnet. These SCFs with different thicknesses were grown using the liquid phase epitaxy method onto: (i) undoped Gd₃Ga_2.5Al_2.5O₁₂ (GAGG (2.5)) substrates; (ii) Ce³⁺ doped Gd₃Ga_2.5Al_2.5O₁₂ (GAGG:Ce (2.5) and Gd₃Ga₃Al₂O₁₂ (GAGG:Ce (3) substrates. For the first time, we have examined the phosphor conversion properties of the mentioned film and film-crystal converters under the excitation of a blue LED. We have established a trend line in the color coordinate diagram by systematically varying the film thickness in the 2–30 μm, 17–22 μm and 7–22 μm ranges for CSSG:Ce film/GAGG (2.5) crystal, CSSG:Ce film/GAGG:Ce (2.5) crystal and CSSG:Ce film/GAGG:Ce (3) crystal composite converters, respectively.

In the present paper, we study the optical, electrical, and sensing properties of titanium dioxide (TiO₂) film deposited on glass plates using a vacuum coating technique (High Hind Vacuum). The optical properties were studied using UV–visible and the result found that the band gap of fabricated thin film is 3.3 eV. The structural properties of the deposited film have been explored by XRD. XRD measurement revealed that the crystallite size is 25.7 nm and it showed that the deposited film is anatase phase and nanometric range. The experimental work was done for the study of LPG sensing properties at 300 K in the laboratory. Results found that the TiO₂ film fast response/recovery time (91 s/180 s) and a maximum response of 29 % toward LPG.

A semi-empirical method is introduced to estimate the emission energy of the Mn⁴⁺ ion in fluorides and oxides without using spectroscopic data as inputs. The method is based on the calculation of the nephelauxetic function he at the octahedral crystal sites occupied by the Mn⁴⁺ cations in the considered host lattices. Only structural data are required for this calculation. The model reproduces the experimental emission energy of Mn⁴⁺ in 51 tested fluorides and 101 tested oxides within ±300 cm⁻¹ in 98% of the fluorides and within ±500 cm⁻¹ in 85% of the oxides. The accuracy is lowered as the he value, i. e. the covalency of the Mn–O bonding, is raised.

Cerium doped (Lu,Y)₂SiO₅ (or LYSO) single crystals have been studied by means of luminescence excitation spectroscopy in the temperature range from 7 up to 300 K. Vacuum ultraviolet excitations in 4.5–8 eV energy range from synchrotron radiation of 1.5 GeV storage ring of MAX IV synchrotron facility. It is shown that both type of Ce³⁺ emission centers (seven and six coordinated centers) are excited under any excitation energy used. It was concluded that the same energy transfer processes from host lattice to impurity ions are involved independently on coordination of Ce³⁺. It is also demonstrated that excitonic mechanism of energy transfer is dominant under chosen excitation and intrinsic and bound excitons are included in excitation of Ce³⁺ luminescence in LYSO.