Co-doped Y3Al5O12 Research Articles

Investigation of a thermally robust orange-red MgO-YMASG: Ce composite phosphor ceramic for white light LED/LD illumination

With its distinctive ability to emit red light with a wavelength surpassing 600 nm, Mg2+-Si4+ co-doped Y3Al5O12: Ce (YMASG: Ce) ceramics emerge as superior candidates for achieving high color rendering and high power white light illumination compared to YAG ceramics. However, due to its higher Stokes energy loss, the orange-red phosphor ceramic YMASG: Ce encounters more pronounced thermal accumulation issues when excited by high-power blue light LEDs/LDs. In response to this challenge, we employed vacuum solid-state sintering technology to fabricate MgO-YMASG: Ce composite phosphor ceramics. As the MgO content increased from 0 to 30 wt%, the thermal conductivity of the samples rose from 5.13 W/(m∙K) to 8.96 W/(m∙K). Additionally, the lower refractive index of MgO effectively enhanced the light extraction efficiency of the ceramics. Consequently, even at a 30 wt% MgO content, the luminescent efficiency of the sample remained comparable to that of YMASG: Ce phosphor ceramics. This suggests that MgO-YMASG: Ce composite phosphor ceramics can serve as high thermal robust orange-red phosphor materials for white light LED/LD illumination.

The role of co-dopant Ce3+ on the spectral properties of Dy3+ activated YAG single crystal for yellow green laser application

Ce3+ and Dy3+ co-doped Y3Al5O12 (abbr. as Ce, Dy: YAG) single crystal was grown by the Czochralski method. As compared with the absorption spectrum of Dy: YAG crystal, the synchronous doping of Ce3+ ions into Dy: YAG crystal resulted in a wide excitation band in the 425–500 nm region peaking around 447 nm owing to the 4f→5d transition of Ce3+ ions, and inhomogeneous broadening absorption with the full width at half maximum (FWHM) from 4 nm to 39 nm. Furthermore, due to the efficient energy transfer from Ce3+ to Dy3+ ions in YAG crystal, under 447 nm excitation Ce, Dy: YAG crystal showed intense and wide characteristic yellow green emission, whose intensity increased by 12.3 times and FWHM from 12 nm to 113 nm as compared with Dy: YAG crystal. The fluorescence lifetime of Dy3+: 4F9/2 level has increased from 693.1 μs to 2.062 ms. Based on the above results, Ce, Dy: YAG crystal would be an excellent candidate for the realization of yellow green waveband laser output.

Analyses of energy transfer of Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic powders at the 4 T 1 level of Cr3+ ion excitation

The concentration dependence of energy transfer from Cr3+ to Nd3+ at the 4 T 1 level excitation in Nd/Cr:YAG was investigated by the fluorescence decay curves of Cr3+ and Nd3+ for Nd/Cr:YAG and Cr:YAG ceramic powders in the Cr3+ concentration range of 0.1–6.0 mol%. The energy transfer process between Cr3+ and Nd3+ at the 4 T 1 level excitation is tried to explain using a rate equation that assumes energy transfer from the 2 E–4 T 2 level to Nd3+ on the basis of dipole–dipole interactions, the same as the 4 T 2 level excitation. In conclusion, the energy excited to the 4 T 1 level will relax non-radiatively to the 2 E–4 T 2 level and then transfer to Nd3+. It is presumed there will be no direct transfer from the 4 T 1 level to Nd3+. Our rate equations will be useful when simultaneously exciting the 4 T 1 and 4 T 2 levels of Cr3+ in Nd/Cr:YAG using broadband pumping sources.

Yb3+/Mn2+ co-doped Y3Al5O12 phosphors for optical thermometric application

Yb3+/Mn2+ co-doped Y3Al5O12 phosphors are prepared by the high-temperature solid-phase reaction via sintering the raw materials at 1600 °C in reducing atmosphere. Orange-red up-conversion (UC) emission of Mn2+ was observed at room temperature. Under the 980 nm excitation, the orange UC emission band peaked at 585 nm was realized, which came from the 4T1(4G) → 6A1(S) transition of cooperative luminescence of Yb3+-Mn2+ dimers. Due to rapid decrease of the UC emission intensity with increasing temperature, high absolute sensitivity (Sa) and relative sensitivity (Sr) were obtained. The maximum value of Sa is 0.017 K−1 at 423 K, and the maximum value of Sr is 3.4% K⁻1 at 423 K. All the Sr value were over 1.7% K−1 in the range from 298 K to 423 K. The thermal reliability was 95.2% at 423 K and 96.9% at 298 K, respectively. In summary, YAG:Yb3+, Mn2+ can be a reliable candidate for optical temperature sensing.

Enhanced 1.5 µm emission of Tm3+ ions by co-doping Tb3+ ions in Y3Al5O12 ceramics

Tm3+ and Tb3+ co-doped Y3Al5O12 (YAG) ceramics were fabricated by high temperature solid state reaction under oxygen sintering. The absorption spectra, fluorescence spectra and fluorescence decay curves of Tm,Tb:YAG ceramics were measured. The spectral parameters of Tm,Tb:YAG ceramic were calculated. The lifetimes of Tm3+:3F4 level of Tm,Tb:YAG ceramics were calculated to be 11.28, 2.12, 1.24, 0.63 and 0.49 ms for the Tb3+ doping concentration of 0, 0.1, 0.2, 0.35 at 0.5 at%, respectively. The co-doping Tb3+ ion is a productive deactivator that could reduce the filling of 3F4 mainfold and enhance the emission of 3H4→3F4 transition. These results indicate that the addition of Tb3+ ions in Tm,Tb:YAG ceramic could be a promising technique for laser operation around 1.5 µm.

Temperature dependence of the small-signal gain of a Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic

There is a demand for higher-efficiency neodymium and chromium co-doped yttrium aluminum garnet (Nd/Cr:YAG) ceramics that can be excited by broadband light sources, such as flash lamps. We experimentally investigated the temperature dependence of the gain coefficient of a Nd/Cr:YAG ceramic (Nd: 1.0 at%, Cr: 2.0 at%). The gain coefficient at 1064 nm decreased with increasing temperature when Nd3+ was directly excited at 808 nm. However, when Nd3+ was excited via energy transfer from Cr3+ excited at 610 nm, the gain coefficient increased with increasing temperature. This temperature dependence was theoretically explained by solving the rate equations for Nd/Cr:YAG. Nd/Cr:YAG ceramics pumped with flash lamps may provide good laser performance without loss of gain even at high temperatures.

Growth and optical properties of the Nd,Ce:YAG laser crystal

A high-quality 2-inch-diameter Nd3+, Ce3+ co-doped Y3Al5O12 (YAG) crystal was successfully grown by the Czochralski (CZ) method. During crystal growth, a modified temperature field was applied to prevent defects in the crystal. The spectrum of the sample showed strong absorption peaks corresponding to Nd3+ and Ce3+ ions. The effect of Ce3+ codoping on the photoluminescence of Nd3+ was investigated in detail. Strong 1066 nm emission of Nd3+4F3/2–4I11/2 was observed upon the 5d excitation of Ce3+. The energy transfer from Ce3+ to Nd3+ consists of nonradiative and radiative components. Compared to Nd:YAG, the double-doped Nd,Ce:YAG crystal realizes better utilization of the pump energy and higher laser energy output. Moreover, the laser threshold value is also significantly reduced. These results imply that Ce3+ doped into the YAG crystal acts as a good sensitizing ion for Nd3+. Hence, this double-doped Nd,Ce:YAG crystal is expected to be of industrial significance for manufacturing high-energy, low-volume solid-state lasers.

Concentration-dependent fluorescence decay and energy transfer in Cr3+ and Nd3+ co-doped Y3Al5O12 ceramic powder

Energy transfer from Cr3+ to Nd3+ in Cr3+ and Nd3+ co-doped Y3Al5O12 (Nd/Cr:YAG) was investigated by measuring the decay curves of Nd3+ and Cr3+ fluorescence for Cr:YAG and Nd/Cr:YAG ceramic powder samples that were produced by the sol–gel method in a Cr3+ concentration range of 0.1–6.0 mol%. The energy transfer processes in Nd/Cr:YAG could be explained based on dipole–dipole interactions even when the concentration quenching of Cr3+ was included, and the experimental fluorescence decay characteristics of Nd3+ excited through Cr3+ were consistent with the theoretical predictions based on dipole–dipole interactions. For a high-quality Nd/Cr:YAG ceramic with negligible concentration quenching, the energy transfer efficiency from Cr3+ to Nd3+ increased with an increase in Cr3+ concentration.

Tailoring the 3F4 level lifetime in Tm3+: Y3Al5O12 by Eu3+ co-doping for signal processing application

Tm3+: Y3Al5O12 (Tm:YAG) crystal is a promising material for high-resolution spectral analysis of broadband radio-frequency (RF) signals, where the absorption spectrum is modified via spectral hole burning. In Tm:YAG, the efficiency of the spectral tailoring is limited by the long-lived metastable level 3F4, acting as a bottleneck for the optical pumping mechanism. We demonstrate that co-doping Tm:YAG with Eu3+ ions can significantly shorten the optical lifetime of 3F4 state, while that of 3H4 is essentially conserved. We show with a model that these modified lifetimes allow faster tailoring of the absorption profile. Because of their low cost and easiness of processing, we use Tm3+ and Eu3+ co-doped Y3Al5O12 ceramics to probe the energy transfer efficiency and find the optimal cation co-doping concentration. Furthermore, we show that Eu3+ co-doping increases the inhomogeneous broadening on the Tm3+ optical transition, hence the spectral analysis bandwidth. Finally, we confirm these results on a single crystal grown by the Czochralski method.

Tb3+ to Cr3+ energy transfer in a co-doped Y3Al5O12 host

Strong absorption and high quantum efficiency are the key features for any phosphor. Chromium and terbium co-doped yttrium aluminum garnets (YAGs) are perfect candidates for luminescence. All samples of singly doped and co-doped YAG were prepared by the aqueous sol-gel route, which is advantageous and useful to obtain single phase garnets. Samples were annealed at 1500 °C in order to minimize crystal lattice defects and to obtain better luminescence properties. An efficient energy transfer from Ce3+ to Tb3+ ion was observed in the co-doped YAG phosphors. It was found that optimal Tb3+ doping concentration in YAG:x%Tb3+ was x = 1%, with external quantum efficiency (EQE) of nearly 71%. Optimal Tb3+ co-doping concentration in YAG:1%Cr3+,x%Tb3+ was x = 15%, with EQE of more than 98% (excited at 273 nm). All series of samples of YAG:Tb3+ and YAG:Cr3+,Tb3+ were characterized by X-ray diffraction (XRD) analysis, steady state and kinetic luminescence measurements.

Effects of Mg2+/Si4+ doping on luminescence of Y3Al5O12:Ce3+ phosphors

A series of Mg2+/Si4+ codoped Y3Al5O12:Ce3+ phosphors were synthesized by a sol-gel method. X-ray diffraction, scanning election microscope, energy dispersive spectroscopy and fluorescent spectrophotometer were used to characterize the synthesized phosphors. The influence of codoped Mg2+/Si4+ ions on luminescence of Y3Al5O12:Ce3+ was investigated. The X-ray diffraction, scanning election microscope and energy dispersive spectroscopy results indicate that Ce3+, Mg2+ and Si4+ substitute Y3+ site, Al13+ in the octahedral site and Al23+ in the tetrahedral site and the substitution has no obvious influence on the phase and microstructure. And the Mg2+/Si4+ substitution leads to the red shift of emission band and the decrease of emission intensity.

The Impact of Cr3+ Doping on Temperature Sensitivity Modulation in Cr3+ Doped and Cr3+, Nd3+ Co-doped Y3Al5O12, Y3Al2Ga3O12, and Y3Ga5O12 Nanothermometers.

A new approach to enhance the sensitivity of transition metal ion based nanocrystalline luminescent thermometer is presented. It was shown that the increase of Cr3+ concentration in three types of garnet host namely Y3Al5O12, Y3Ga5O12, and Y3Al2Ga3O12 allows for significant enhancement of their performance in non-contact thermometry. This phenomenon is related to the weakening of the crystal field strength due to enlargement of average Cr3+-O2− distance at higher Cr3+ concentrations. By increasing Cr3+ concentration from 0.6 to 30%, the sensitivity increased by over one order of magnitude from S = 0.2%/°C to S = 2.2%/°C at 9°C in Y3Al2Ga3O12 nanocrystals. Moreover, it was found that due to the Cr3+ → Nd3+ energy transfer in the Cr3+, Nd3+ co-doped system, the usable Cr3+ concentration, for which its emission can be detected, is limited to 10% while the sensitivity at −50°C was doubled (from 1.3%/°C for Y3Al2Ga3O12:10%Cr3+ to 2.2%/°C Y3Al2Ga3O12:10%Cr3+, 1%Nd3+ nanocrystals).

Effect of Si4+ substitution on luminescence of Y3Al5O12:Mn4+

The synthesis, luminescence, and potential applications in white light diodes of Mn4+/Si4+ codoped Y3Al5O12 phosphors are presented. The Mn4+ doped Y3Al5O12 phosphor shows the deep red emission with a strongest emission peak at about 646 nm. By codoping Si4+ in Y3Al5O12:Mn4+, the intensity and peak wavelength of Mn4+ emission are tuned. The appropriately codoped Si4+ can enhance the Mn4+ emission intensity due to the formation of Mn4+-Si4+-O2- pairs. The formed Mn4+-Si4+-O2- pairs interrupts the energy migration from Mn4+ to O2- quenching centers. The codoped Si4+ also induces the blue shift of Mn4+ emission since the substitution of Al23+ by smaller Si4+ leads to a longer Mn-O bond length.

Broadband down-conversion of near-infrared emission in Bi3+-Yb3+ co-doped Y3Al5O12 phosphors

An efficient near-infrared (NIR) down-conversion (DC) process has been demonstrated in Bi3+-Yb3+ co-doped Y3Al5O12 phosphors. The excitation spectra, emission spectra and decay curves were measured to prove the occurrence of energy transfer (ET) from Bi3+→Yb3+. Upon the excitation of UV photons, NIR emission has been obtained at 1028nm through the energy transfer from 3P1 energy level of Bi3+ to 2F5/2 energy level of Yb3+. Quantum efficiency related to Yb3+ concentration is calculated and the maximum efficiency reaches 138%. Our results suggested that these phosphors might have a potential application for the down-conversion process to improve the efficiency of Si-based solar cells.

Doping effect of Tb3+ ions on luminescence properties of Y3Al5O12:Cr3+ phosphor

Tb3+or/and Cr3+ doped or co-doped Y3Al5O12(YAG) garnets were prepared by a citric acid sol–gel method. Single-phase YAG, YAG:Tb3+,YAG:Cr3+and YAG:Cr3+,Tb3+powders were obtained already at 1000°Cand were further annealed at 1600°C to increase the crystallinity. All materials were characterized by X-ray diffraction (XRD), thermogravimetric (TG), photoluminescence (PL), reflection and photoluminescence decay measurements. Scanning electron microscopy (SEM) was used for morphology description. Luminescence measurements indicated that Tb3+ ions located at dodecahedral sites transfer absorbed energy to Cr3+ ions located at octahedral sites resulting quenched Tb3+ and strengthened Cr3+ emission in YAG:Cr3+, Tb3+ upon 273nm excitation.

A Novel Single-Component White-Emitting Tb and Mn Co-Doped Large-Sized Y3Al5O12:Ce3+ Single Crystal for White LED

A Novel Single-Component White-Emitting Tb and Mn Co-Doped Large-Sized Y₃Al₅O₁₂:Ce³⁺ Single Crystal for White LED

The growth and luminescence properties of Y3Al5O12:Ce3+ single crystal by doping Gd3+ for W-LEDs

Transparent Ce3+ and Gd3+ co-doped Y3Al5O12 (Ce,Gd:YAG) single crystal (SC) was successfully grown by the Czochralski method. Meanwhile, the structures and optical properties of single crystal wafers (SCWs) were investigated. When Y3+ ions were partially substituted by Gd3+ ions, the emission peak shifted towards the long wavelength direction. Compared with commercial phosphors, SCWs not only showed excellent thermal stability, but also exhibited superior optical performance with a luminous efficacy of 144.11lm/W, a correlated color temperature of 5639K and a color rendering index of 69.9.

Temperature Dependent Energy Transfer in Ce3+-Yb3+ Co-Doped YAG Phosphors

Ce3+-Yb3+ co-doped Y3Al5O12 (YAG) phosphors were prepared, and their photoluminescence spectra, photoluminescence excitation spectra and fluorescence decay curves were measured at different temperatures from 8 K to 300 K. Experimental results show that, besides thermal quenching effect, the energy transfer is also the mechanism for the temperature dependence of the Yb3+ emission. A photo-induced Ce-O-Yb charge transfer state model is proposed to explain the variation of the emission with the temperature. The decay curves of the co-doped YAG phosphors at different temperatures can also be explained by the model.

High infrared emission property of Ca<sup>2+</sup>/Cr<sup>3+</sup> co-doped Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> ceramics

High infrared emission property of Ca<sup>2+</sup>/Cr<sup>3+</sup> co-doped Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> ceramics

Computational discovery of lanthanide doped and Co-doped Y3Al5O12 for optoelectronic applications

We systematically elucidate the optoelectronic properties of rare-earth doped and Ce co-doped yttrium aluminum garnet (YAG) using hybrid exchange-correlation functional based density functional theory. The predicted optical transitions agree with the experimental observations for single doped Ce:YAG, Pr:YAG, and co-doped Er,Ce:YAG. We find that co-doping of Ce-doped YAG with any lanthanide except Eu and Lu lowers the transition energies; we attribute this behavior to the lanthanide-induced change in bonding environment of the dopant atoms. Furthermore, we find infrared transitions only in case of the Er, Tb, and Tm co-doped Ce:YAG and suggest Tm,Ce:YAG and Tb,Ce:YAG as possible functional materials for efficient spectral up-conversion devices.