Garnet Phosphors Research Articles

Neodymium(III)-doped Y<sub>3</sub>Al<sub>2</sub>Ga<sub>3</sub>O<sub>12</sub> garnet for multipurpose ratiometric thermometry: From cryogenic to high temperature sensing

Nd3+-doped Y3Al2Ga3O12 garnet ceramic pellet was prepared by solid state reaction and used as prototype to investigate the potential of Nd3+-activated garnet phosphors as Boltzmann thermometers for cryogenic and high temperature ranges. Despite the conventional use of the near-infrared emitting Nd3+-activated phosphors for biological applications, their real use is hindered by a low sensitivity in the physiological temperature range. Instead, the photoluminescence analysis in the 100–800 K range demonstrated interesting performances in both the cryogenic and high temperature ranges. Indeed, by taking advantage of the Stark levels of 4F3/2 (Z-levels) and the ratio between the emission from the 4F5/2 and the 4F3/2 excited states is possible to build two reliable Boltzmann thermometers in the same material working in the cryogenic temperature range (100–220 K) and at high temperatures (300–800 K), respectively.

Effect of down-shifting phosphor particles on crystalline silicon solar cells

Introducing down-shifting phosphor particles onto solar cells can improve their spectral response to short wavelength photons, but it also leads to the rise of reflection in middle and long wavelength range due to the scattering by phosphor particles. In this work, the down-shifting solar cells are fabricated by packaging crystalline silicon solar cells with ethylene vinyl acetate (EVA) films which include different concentration of down-shifting Ce-doped yttrium aluminum garnet (YAG:Ce) phosphor particles. Experimental result shows that the increasing concentration of YAG:Ce phosphors strengthens the down-shifting effect and makes the reflection rise. The competition between the down-shifting effect and the reflection results in the best improvement of the solar cells when the phosphor's concentration is 0.7%. The optical ray-tracing simulations clarify that the packaged solar cell with YAG:Ce absorbs less photons than those without YAG:Ce, but their conversion efficiency is higher than those without YAG:Ce. This indicates that the penetration depth of the short wavelength photons is responsible for the poorer spectral response of the solar cells in the short wavelength range.

Sintering YAG:Ce phosphor ceramic layers onto glass substrates by CO2 laser for WLED applications

Cerium-doped yttrium aluminum garnet (YAG:Ce) phosphor layers were sintered onto glass using CO2 laser. The layer adhesion was found to depend on the spin coating thickness. The x-ray diffraction indicated the formation of YAG phase, with minor impurities of Y2SiO5 and Y4Al2O9. When the coating thickness was 65 μm, the laser beam reacted thoroughly with glass and YAG precursors, and a liquid phase was formed, producing a thin amorphous layer (∼5 μm) on the surface grooves. However, when the thickness was increased to 170 μm, the laser beam could not penetrate to react entirely with YAG precursors, resulting in more raw residues and poor adhesion. The sintered YAG:Ce phosphor layers on glass were characterized via photoluminescence, presenting yellow emission with a thermal quench to 75% at 125 °C, which is comparable to that of the solid-state reacted YAG:Ce ceramics.

Development of ultra-broad band light emitting single phase garnet phosphor based on energy transfer mechanism and its applications in optical temperature sensing and WLED

Cerium (Ce3+) doped garnet phosphor has received much attention for optoelectronic device applications. However, the family of Ce3+ doped garnet phosphors suffers from deficiency of red component in their emission spectrum. Herein, authors present a strategy to improve red component through widening of emission band with the incorporation of Cr3+ co-dopant in the garnet structure. In view of this authors have prepared a series of Ce3+ doped and Ce3+/Cr3+ co-doped Gd3Al4GaO12 (GAGG) garnet using the facile solid state reaction method. The structural studies of prepared garnet is done with the help of X-ray diffraction (XRD) study. The photoluminescence study demonstrates that Ce3+/Cr3+ co-doped garnet sample emits an ultra-broad emission band ranging from 490 nm to 850 nm under suitable excitations. The ultra-broad band is observed due to the combination of emission bands originating from the transitions of Ce3+ and Cr3+. The Ce3+/Cr3+ co-doped garnet sample is also studied to examine the optical thermometric ability with the help of the luminescence intensity ratio (LIR) technique. Finally, the selected samples with optimized compositions GAGG: 6.0 %Ce3+ and GAGG:6.0 %Ce3+/1.5 %Cr3+ were used to fabricate pc-WLED device by the coating of phosphor layer over commercially available blue LED chip (InGaN). The fabricated pc-WLED device has shown good voltage stability as well as good LED performance parameters CRI (>70) and CCT (<4000K) values. Present results may stimulate the exploration of optical tuning via the incorporation of additional dopants such as Cr3+ in Ce3+ doped garnet phosphor for optical thermometry and pc-WLED.

Synthesis and photoluminescence properties of garnet red emitting CaY2Al4SiO12:Eu3+ phosphors

Eu3+ doped CaY2Al4SiO12 garnet phosphors were synthesized by using the sol-gel method. The crystal structure of the synthesized phosphors was characterized by X-ray diffraction and Rietveld refinements. The results of X-ray diffraction and Rietveld refinements of the powders sintered at 1400 °C showed the formation of a single phase and the effective concentration of Eu3+ ions in this garnet host lattice.The composition of the substitutional solid solutions of CaY2-xEuxAl4SiO12 (x = 0.01, 0.03, 0.06, 0.09, 0.12, and 0.15) exhibit efficient red photoluminescence peaking at 596 nm, which can be assigned to the 5D0 → 7F1 intra-configurational transition of Eu3+ located at the dodecahedral site in the garnet structure. The photoluminescence properties, such as excitation and emission spectra, decay curves, and quantum yield, are presented. The thermal stability of the as-prepared phosphors was determined. Additionally, the optical bandgap for the samples was estimated with UV–visible diffuse reflectance spectra using the Tauc relation. The correlation between the structural features and luminescence properties was determined. These phosphors with high thermal stability and high color purity can be potentially used in white-light-emitting diodes.

An efficient blue-excitable broadband Y3ScAl4O12:Ce3+ garnet phosphor for WLEDs.

Most commercial phosphor-converted white light-emitting diodes (pc-WLEDs) are manufactured with blue LED chips and yellow-emitting Y3Al5O12:Ce3+ (YAG:Ce3+) garnet phosphor, but the lack of blue-green light in the spectrum results in a low color rendering index (CRI). In this paper, we synthesized Y3ScAl4O12:Ce3+ (YSAG:Ce3+) by replacing Al3+ in YAG:Ce3+ with Sc3+. The introduction of Sc3+ with a larger ionic radius through a cation substitution strategy causes lattice expansion, elongation of the Y-O bond, and ultimately a decrease in Ce3+ 5d level crystal field splitting. As a consequence, the emission spectrum undergoes a blue-shift of 10 nm. Furthermore, the YSAG:Ce3+ phosphor exhibits good thermal stability, and its emission intensity at 423 K is about 58% of that at 303 K. Moreover, the analysis of Eu3+ emission spectra demonstrates that the introduction of Sc3+ resulted in a slight reduction of the dodecahedral lattice symmetry. YSAG:Ce3+ effectively compensates for the lack of the blue-green region, and WLEDs with high color rendering index (90.1), low color temperature (4566 K) and high luminous efficiency (133.59 lm W-1) were prepared using the combination of YSAG:0.08Ce3+, CaAlSiN3:Eu2+ and 450 nm blue chips. These findings indicate that YSAG:Ce3+ garnet phosphor has potential to be used in high quality WLEDs.

An efficient and thermally stable Cr3+-activated Y2GdSc2Al2GaO12 garnet phosphor for NIR spectroscopy applications.

Near-infrared (NIR) spectroscopy realized by an NIR phosphor-converted light-emitting diode (pc-LED) as a light source has aroused considerable interest due to its numerous merits and widespread application scenarios. Nevertheless, developing NIR emitting phosphors with high performance is still the top priority. Here, we report a new Y2GdSc2Al2GaO12:Cr3+ (YGSAG:Cr3+) garnet phosphor, which demonstrates a broadband emission peaking at 754 nm with a full width at half maximum (FWHM) of around 120 nm in the range of 650-1200 nm. The YGSAG:0.08Cr3+ sample irradiated by blue light exhibits the most intense emission intensity, leading to a high absorption efficiency of 49.54%. In addition, compared with room temperature, the integrated PL intensity of the sample can still be maintained at 90.97% at 423 K. Benefitting from the outstanding optical properties, the as-manufactured NIR pc-LED device driven by a 100 mA current represents a high NIR output power of 35.14 mW and a photoelectric efficiency of 12.51%. These results verify that the as-synthesized YGSAG:Cr3+ phosphor possesses great potential for the applications of NIR spectroscopy.

Temperature sensing of Sr3Y2Ge3O12:Bi3+,Sm3+ garnet phosphors with tunable sensitivity.

In this study, a novel temperature-sensitive material, Sr3Y2Ge3O12:Bi3+,Sm3+ phosphor, was successfully synthesized by a solid-state reaction method. Under 376 nm light excitation, the as-prepared phosphor presents both blue emissions of Bi3+ and orange red emissions of Sm3+ due to energy transfer from Bi3+ to Sm3+. Owing to the significant difference in thermal quenching properties and the distinguishable emission between Bi3+ and Sm3+ ions, the temperature sensing performance of the prepared phosphor was evaluated by measuring the fluorescence intensity ratio (FIR) of Sm3+versus Bi3+. More importantly, for the first time, it was found that the absolute and relative sensitivities of Sr3Y2Ge3O12:Bi3+,Sm3+ could be tuned by changing the concentration of activators to determine the optimal temperature measurement conditions, which opened up the possibility of improving the performance of fluorescence temperature sensing materials.

Augmenting cyan emission in vanadate garnets via Dy3+activation for light emitting devices and multi-mode optical thermometry.

Developing cyan-based phosphors is inevitable to bridge the cyan gap to generate white light with a high color rendering index. Herein, the blue-green emission from the VO43- center in the Sr2NaMg2V3O12 host is augmented via activating with Dy3+ ions. Dual emission from the Sr2NaMg2V3O12:Dy3+ system under 335 nm excitation is due to the energy transfer from VO43- to the Dy3+ center. An increase in the ratio of yellow to blue bands (Y/B) is noted with the increase in the concentration of Dy3+. Apart from the higher activation energy of 0.41 eV, excellent color stability with a small thermochromic shift is noted at elevated temperatures. The light emitting device fabricated based on the Sr2NaMg2V3O12:Dy3+ phosphor presents bright cyan emission with CIE coordinates of (0.250, 0.352), a CCT of 9826 K, and a CRI of 53 with stable emission even at higher input currents. The application of Sr2NaMg2V3O12:Dy3+ in multi-mode temperature sensing is also discussed. The maximum relative temperature sensitivity of 1.32, 0.41, and 1.9% K-1 at 380, 300, and 460 K is obtained for the fluorescence, fluorescence intensity ratio and excitation intensity ratio methods. Thus, the present work details the capability of Dy3+-based vanadate garnet phosphors for solid-state lighting and temperature sensing.

Delving into the multifunctionality of Sr2NaMg2V3O12via RE3+ substitution for dual-mode temperature sensing, latent fingerprint detection and security inks

Multifunctionality of vanadate garnet phosphors in latent fingerprint detection, security inks, and dual-mode temperature sensing.

Smaller Stokes Shift Induced Highly Efficient Broadband Near Infrared Garnet Phosphor

AbstractBroadband near‐infrared (NIR) phosphor converted light emitting diodes (pc‐LEDs) are novel compact light sources that enable portable devices for substance detection. However, to achieve such efficient pc‐LEDs is still a challenge due to lack of efficient phosphors. In this paper, Stokes shift as an efficiency predictor is emphasized. In Cr3+ activated Ca2LuZr2Al3O12 (CLZA) garnet phosphor, Stokes shift decreases from 2990 to 2854 cm−1 upon substituting Ca‐Zr with Lu‐Al. As a result, electron–phonon coupling related nonradiative process is reduced. The external quantum efficiency is significantly enhanced to 47.4%, and the as fabricated NIR pc‐LED offers 33.7% @10 mA electro‐optical efficiency. The results can advance the development of efficient NIR phosphors.

Improving light output by micro-TiO2 scatters in pc-WLED encapsulants.

Phosphor-converted white light emitting diodes (pc-WLEDs) are used worldwide for an extensive amount of applications. The device is a complex combination of various components that introduce various technical issues: materials, electrical, chemical, thermal, and so on. All of these combined to obtain a targeted optical characteristic. While most of the pc-WLEDs are sufficient for basic illumination performance, there are still many issues to improve the pc-WLED performance. In this work, we deal with the incorporation of micron size particles of titanium oxide (TiO2) in silicone encapsulant that contains yttrium aluminum garnet (YAG) phosphor in remote phosphor pc-WLED. Based on the light output and the scattering spatial distribution measurements of the phosphor plates, we have found that several essential performance indices, like the color uniformity, the efficiency, and the amount of phosphor for the pc-WLEDs, can be adjusted by tuning the amount of TiO2 particles and thus be optimized. With a comprehensive model using a Monte-Carlo ray tracing process combined with the Mie scattering theory, two TiO2 loading conditions are revealed. The first one is the sparse condition that the TiO2 particles act as the scattering particles such as to increase the output flux to improve the efficiency of YAG. The second one is the dense condition that the TiO2 particles act more as barrier particles such so to decrease the output flux.

A highly efficient and broadband near-infrared-emitting garnet phosphor for plant lighting realized by cation co-substitution in lutetium aluminum garnet

Near-infrared phosphor-converted light emitting diodes (NIR pc-LEDs) is developing rapidly in plant cultivation because of its low cost, compact size and high efficiency. The NIR light of 700 ∼ 760 nm is known to be beneficial for seed germination and growth. Therefore, the exploration of NIR phosphors with specific wavelength and high efficiency is essential for the development of high-performance plant cultivation pc-LEDs. In this study, a highly efficient and thermal stable Cr3+ doped Lu2CaAl4SiO12 (LCAS) phosphor with broadband NIR emission covering phytochrome Pfr absorption range was successfully realized via Ca2+-Si4+ co-substitution of Lu3+-Al3+ pairs. The LCAS:0.07 Cr3+ exhibits a major emission peak of 740 nm with a FWHM of 160 nm and its internal/external quantum yield (IQY/EQY) is as high as 80%/30.5%. The integrated emission intensity of LCAS:0.07Cr3+ at 423 K lost only 33.8% of its initial intensity, indicating that it has a good thermal stability. When the LCAS:0.07Cr3+ was packaged into a pc-LED with a driving current of 320 mA, the device output power and photoelectric efficiency reached 90.6 mW and 8.6%, respectively, demonstrating that this phosphor has potential application in plant cultivation lighting.

Enhanced Photoluminescence of Gd3Al4GaO12: Cr3+ by Energy Transfers from Co-Doped Dy3.

LEDs for plant lighting have attracted wide attention and phosphors with good stability and deep-red emission are urgently needed. Novel Cr3+ and Dy3+ co-doped Gd3Al4GaO12 garnet (GAGG) phosphors were successfully prepared through a conventional solid-state reaction. Using blue LEDs, a broadband deep-red emission at 650−850 nm was obtained due to the Cr3+ 4T2 → 4A2 transition. When the Cr3+ concentration was fixed to 0.1 mol, the crystal structure did not change with an increase in the Dy3+ doping concentration. The luminous intensity of the optimized GAGG:0.1Cr3+, 0.01Dy3+ was 1.4 times that of the single-doped GAGG:0.1Cr3+. Due to the energy transfer from Dy3+ to Cr3+, the internal quantum efficiency reached 86.7%. The energy transfer from Dy3+ to Cr3+ can be demonstrated through luminescence spectra and fluorescence decay. The excellent properties of the synthesized phosphor indicate promising applications in the agricultural industry.

Ultra-broadband near-infrared Gd3MgScGa2SiO12: Cr, Yb phosphors: Photoluminescence properties and LED applications

Developing novel broadband near-infrared (NIR) phosphors is crucial to promote NIR phosphor-converted light emitting diodes (pc-LEDs) development. In this work, a new ultra-broadband NIR phosphor Gd 3 MgScGa 2 SiO 12 : Cr 3+ (GMSGS) was achieved by replacing Sc 3+ -Ga 3+ in Gd 3 Sc 2 Ga 3 O 12 with Mg 2+ -Si 4+ . Under the excitation of blue light, the peak emission wavelength of GMSGS: 0.04Cr 3+ is about 820 nm with a full width at half maximum (FWHM) of ∼180 nm and an internal quantum efficiency (IQE) of 50 %. Benefited from the superposition of Cr 3+ emission and highly efficient Yb 3+ emission excited by energy transfer (ET) from Cr 3+ , the codoped GMSGS: 0.04Cr 3+ , 0.007Yb 3+ phosphor shows an ultra-broadband of 300 nm. Moreover, Yb 3+ -codoping improves the thermal stability due to the ET from Cr 3+ to more thermally stable Yb 3+ emitters, and the integrated intensity of GMSGS: 0.04Cr 3+ , 0.007Yb 3+ at 400 K was 63 % of that at room temperature. The packaging results exhibit that ~20 mW output power was achieved at 100 mA input current, which suggests promising potential of GMSGS: Cr 3+ , Yb 3+ phosphor in NIR pc-LED applications. • A novel broadband NIR garnet phosphor Gd 3 MgScGa 2 SiO 12 :Cr 3+ is developed. • The phosphor shows broadband NIR emissions in 700–1100 nm (λ max = 820 nm). • The phosphor exhibits high quantum yield (~50 %) and good thermal stability. • An ultra-broadband GMSGS: Cr 3+ , Yb 3+ phosphor was achieved owing to the energy transfer from Cr 3+ to Yb 3+ . • The NIR phosphor-converted LED with the NIR output power with ~20 mW at 100 mA drive current is achieved.

Long Persistent Afterglow Luminescence in Gd&lt;sub&gt;3&lt;/sub&gt;Al&lt;sub&gt;3&lt;/sub&gt;Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;12&lt;/sub&gt;:Ce&lt;sup&gt;3+&lt;/sup&gt;, Green Emitting Aluminate Phosphor

Green LL is observed in Ce doped Gd3Al5O12: Ce, Ga garnet phosphors. LL is well correlated with Ce3+ emission and a peak around 150°C in the TL glow curve. In comparison with the commercial phosphor YAG, the Gd3Al5O12: Ce, Ga (GAG) is more stable and shows more intense TL properties, this phosphor can be used for dosimetry detections and measurements. Gd3Al5O12 activated with Ce (0.7 mol.%) phosphors were prepared by combustion synthesis. The long-lasting luminescence (LL) is also reported in Pr3+ and Ce3+ doped in reducing atmosphere in YAG phosphor. But YAG: Ce gives yellow emission which doesn’t suit LL applications. On the other hand, Ga substituted GdAG: Ce phosphor gives green emission at shorter wavelengths. In this paper we explored Ga substituted GdAG: Ce phosphor prepared by combustion synthesis for LL, results of these investigations are reported in this paper.

Photoluminescence Properties of Cyan-Emitting Lu3GaxAl5-xO12: Ce3+ Garnet Phosphors Synthesized in Nonreducing Atmosphere and at Different Temperature for High Quality w-LEDs.

The existence of so-called blue-green cavities in the luminescence spectrum has been a hindrance to the improvement in the performance of traditional phosphor-converted white light emitting diodes. The commercial phosphors synthesized in reducing atmospheres can also cause problems such as equipment complexity, increased cost, and environmental pollution. Herein, a series of cyan-emitting Lu3GaxAl5−xO12: Ce3+ (x = 0, 1, 2, 3, 4) garnet phosphors were synthesized by a traditional solid-state reaction in a nonreducing atmosphere at different temperatures. The crystal structure, grain morphology, optical properties, and thermal quenching behavior were used to analyze the optical properties of the as-prepared phosphors. The luminescence intensity of samples is affected by the synthesis temperature and energy gap between the conduction band and the lowest energy of the 5d excited state of the host lattice. With the substitution of Al3+ by Ga3+, the regularity of the excitation and emission band movement is determined by the combined effects of crystal field splitting (CFS) and the nephelauxetic effect (NE). The temperature dependence of luminescence was studied. The thermal quenching mechanism was clarified by the thermal ionization model. Finally, by employing Lu2.94Ga2Al3O12: Ce3+0.06 as a cyan component, a w-LED with a high color rendering index of 93.2 and low correlation color temperature of 3880 K based on a blue chip and commercial red phosphors were fabricated in order to explore its possible application in high quality w-LED.

Color‐Tunable Single‐Phase Bi3+/Eu3+‐Activated LiCa3ZnV3O12 Luminescence Materials Based on Energy Transfer

AbstractTo achieve high‐quality WLED (White light emitting diodes) lighting, it is essential to accurately control the emission color of phosphor materials. The LiCa3ZnV3O12 : Bi3+/Eu3+ phosphors were synthesized by a traditional high‐temperature sintering reaction and characterized using XRD, SEM, Fluorescence Spectrophotometer. This paper firstly reported the luminescence properties of Bi3+ single‐doped garnet phosphors LiCa3ZnV3O12. Based on local lattice distortion and the energy transfer of VO43−→Bi3+, the luminescence color of LiCa3ZnV3O12 : Bi3+ could be adjusted from blue‐green (490 nm) to yellow‐green (517 nm) under NUV excitation. In addition, Bi3+→Eu3+ energy transfer was designed by Bi3+ and Eu3+ double doping, and full color emission tuning from blue to blue‐green and then to pink and white was successfully realized. The energy transfer mechanism, luminescence chromaticity coordinates and thermal stability are studied in detail. More significantly, by constructing efficient energy transfer between Eu3+ and Bi3+, the thermal stability of as‐synthesized samples are gradually improved. This paper proposes a new direction for the color tuning of phosphors through multiple energy transfers and local lattice distortion.

Enhanced Thermal Stability and Energy Transfer by Crystal‐Field Engineering in a Garnet Phosphor for Thermometry and NIR‐LED

AbstractIt is of significant importance to tailor the luminescent properties of Cr3+ ions as efficient near‐infrared (NIR) emitter for extended optical applications. Here, crystal field engineering is explored to tailor the luminescent properties of a Cr3+‐doped garnet, Lu2Ca1 ‐ xSrxAl4SiO12 (x = 0–1). As Ca2+ is substituted by Sr2+, the emission of Cr3+ becomes sharper with longer lifetime, indicating that the 2Eg→4A2g transition becomes dominant. More importantly, the thermal stability is greatly improved, as the emission intensity at 480 K increases from 83% to 111% of that at 300 K. Moreover, the efficiency of the energy transfer from the Cr3+ to Yb3+/Nd3+ increases from 60–70% to 80–90%. The intensity ratio of I810/I706 from the Lu2SrAl4SiO12:Cr3+,Nd3+ can be applied to thermometry, with the maximum relative sensitivity value of 1.43% K–1 at 303 K. Compared with the blue emission from light‐emitting diode (LED) chip, a clearer and more accurate imaging is established with NIR emission from Cr3+. Furthermore, the intensity ratio of the emissions from the Cr3+ and Yb3+ ions is applied to differentiate pork, chicken, and beef. These findings provide an avenue to optimize the thermal stability and energy transfer of Cr3+‐activated NIR emitters for the applications in thermometry and NIR‐LED.

Photoluminescence properties of far-red emitting Lu2CaAl4GeO12:Cr3+ garnet phosphor

The Cr3+-doped garnet structural phosphors were widely investigated for phosphor-converted light-emitting diode. Here Cr3+ activated Lu2CaAl4GeO12 phosphor with far-red emitting was prepared using the solid-state reaction method. The crystal structure was analyzed employing X-ray diffraction technique. A broad excitation band in the 400–500 nm region was found in the excitation spectrum, which matches well with the chip that emits blue light. The sample exhibits sharp line (2E → 4A2) and broad emission band (4T2 → 4A2) of Cr3+ ions under the 428 nm light excitation. The concentration quenching is mainly caused by the energy transfer between the nearest Cr3+ ions in the host. The thermally stable luminescence was observed by measuring the emission spectra in the temperature range from 300 K to 620 K. The overall emission intensity reaches about 109% at 420 K and maintain 81.4% at 620 K compared to the value at 300 K. This work facilitates the study of Cr3+-doped garnet phosphor with thermally stable far-red emitting.