New Efficient Scintillating and Photoconversion Materials Based on the Self‐Flux Grown Tb₃Al₅O₁₂:Ce Single Crystal

Abstract

Placing the yellow-red emitting luminescent materials directly on top of the blue light-emitting diode (LED) enables for partial conversion of the blue light to red and green or yellow/orange light, and as a result, white light is generated. [1] In 1996, Y 3 Al 5 O 12 :Ce (YAG:Ce) was discovered as an efficient photoconverter (PC) white LED (WLED) phosphor and still is the most widely applied WLED phosphor. [2] To improve cold white light temperature and create warmer WLED, orange or red-emitting phosphor should be used. The substitution of Y for Tb in YAG:Ce leads to the redshift of the Ce 3þ emission. Moreover, Tb 3þ ions efficiently transfer the excitation energy toward Ce 3þ activator, which significantly enhances the luminescence performance of (Tb,Y) 3 Al 5 O 12 :Ce phosphor. [3,4] Consequently, warmer and brighter WLED can be obtained concerning YAG:Ce-based WLED. [5] The redshifted Ce 3þ emission in Tb 3 Al 5 O 12 :Ce (TbAG: Ce) is located at the higher sensitivity range in the scintillation detectors that significantly improve their detection limit. [6,7] Furthermore, TbAG:Ce in the form of powder, ceramics, and single crystal is considered to be a promising candidate for the new generation of efficient scintillators as well as a novel phosphor for warm WLEDs due to possessing high thermal stability of the Ce 3þ luminescence. [8-14] The micro-pulling-down (μ-PD) method is a suitable technology for fast, cheap, and good quality material production for PC WLED [15] and customized size scintillators. [16,17] In the μ-PD method, the crystal is grown from the melt; hence, incongruently melting systems are difficult to fabricate in the pure target phase. [18-23] According to the Al 2 O 3-Tb 2 O 3 phase diagram, the Tb 3 Al 5 O 12 melts incongruently at 2113 K; hence, TbAlO 3 is the most stable phase in this system. [23] Moreover, the crystallization of TbAG consumes relatively more Tb 2 O 3 than contained in the melt. This indicates that the crystallization of TbAG from the melt under strong non-equilibrium conditions might be possible by enriching the melt with alumina. Excess of Al 2 O 3 changes the stoichiometric composition of TbAG and lowers liquidus temperature, increasing the thermodynamic stability of TbAG composition. The segregation coefficients of Tb 3þ and Al 3þ ions in Tb 3 Al 5 O 12 are very far from one. This results in a significant difference between melt and crystal compositions. [19] The ratio of Tb to Al in Tb 3 Al 5 O 12 is 3:5, whereas in TbAlO 3 is 1:1. Consequently, in the Al-rich melt, Tb can be easily surrounded by the proper amount of Al increasing probability of Tb 3 Al 5 O 12 crystallization. However, TbAG can be fabricated in a pure garnet phase using low-temperature synthesis methods, such as solid-state sintering, sol-gel combustion, and liquid phase epitaxy (LPE). [10,14,24,25] This research deals with the melt growth of TbAG:Ce single crystal using the μ-PD method. The crystal was grown from the Tb 3 Al 5 O 12 :Ce nonstoichiometric melt enriched with Al 2 O 3 used as a self-fl...

Novel composite color converters based on Tb1.5Gd1.5Al5O12:Ce single crystalline films and Y3Al5O12:Ce crystal substrates

“…Namely, the bands centered around ∼240 and ∼290 nm belong to the low spin-allowed (LS) 4f → 5d 2 and 4f → 5d 1 absorption transitions of Tb 3+ ions, respectively. 38 Weak absorption bands related with the 4f → 4f Gd 3+ transitions, peaking in the 313–317 nm range, strongly overlap with the bands related to the 4f → 5d (HS) transitions of Tb 3+ ions. The peak at 373 nm is ascribed to the 7 F 6 → 5 G 6 absorption transitions of Tb 3+ cations.…”

“…The peak at 373 nm is ascribed to the 7 F 6 → 5 G 6 absorption transitions of Tb 3+ cations. 38 The photoluminescence emission (PE) and excitation (PLE) spectra of TGAG:Ce/YAG:Ce (S1.2) composite color converters are compared in Fig. 4 with their YAG:Ce SC constituent substrate (S1).…”

Composite Color Converters Based on Tb3Al5O12:Ce Single‐Crystalline Films and Y3Al5O12:Ce Crystal Substrates

“…[23][24][25] Such a bidirectional ET enhances the Ce 3þ emission both in TbAG:Ce SCF and YAG:Ce substrate of the composite color converter under UV or blue LED excitation. [14,26] The Ce 3þ emission spectrum in TbAG:Ce garnet comparing with YAG:Ce counterpart is significantly shifted from 540 to 560 nm. [27,28] The emission redshift is related to increased crystal-field splitting and consequently the larger split of 5d energy level of Ce 3þ ions and the increased Stokes shifts due to the replacement of Y ions (r VIII ¼ 1.019 Å) by larger Tb 3þ (r VIII ¼ 1.04 Å) ions in dodecahedral sites of the garnet structure.…”

“…[10][11][12][13] It is well noted that Tb 3 Al 5 O 12 :Ce (TbAG:Ce) garnet is considered as an outstanding material for phosphor converters (pcs), but the huge difficulties of obtaining this material in SC form greatly complicate their implementation. [14][15][16] Furthermore, the liquid phase epitaxy (LPE) technique allows singlecrystalline films (SCFs) of Tb 3 Al 5 O 12 :Ce in the pure garnet phase to be obtained on undoped or Ce 3þ -doped YAG or Gd 3 Ga 2.5 Al 2.5 O 12 (GAGG) substrates. [17] Meanwhile, weighing all the disadvantages and advantages of PCLC approach, it can be argued here that the single-crystalline garnet still is the most promising phosphor for WLED converter.…”

Towards deliberate design of persistent phosphors: a study of La–Ga admixing in LuAG:Ce crystals to engineer elemental homogeneity and carrier trap depths

“…21 Currently, there is a demand for persistent phosphors that can be charged with daylight and blue light, as many lighting systems use the blue light component in the photoconversion process to generate white light. 22 However, many persistent luminescence phosphors show the strongest persistent luminescence when charged by UV light. 23 Therefore, in the tailoring of persistent phosphors, it is necessary to control the charging energy along with the efficiency of the trapping and the trap depths.…”