Composition and Antithermal Quenching of Noninteger Stoichiometric Eu²⁺-Doped Na-β-Alumina with Cyan Emission for Near-UV WLEDs

Abstract

Phosphors with high quantum efficiency and thermal stability play a key role in improving the performance of phosphor-converted white light-emitting diodes (pc-WLEDs). A near-UV-pumped LED shows a great advantage due to its reduction of the negative effect of blue light on human health. In this work, we propose a series of near-UV excitable cyan-emitting Eu2+-activated phosphors with a nominal composition of Na2–2x Al11O17+a :xEu2+ (x = 0.01–0.40), which crystallize in a sodium β-alumina phase with a composition close to Na1.22Al11O17.11. An excess amount of the sodium carbonate raw material makes up the volatile Na during the high-temperature process. The noninteger stoichiometric composition promotes the rigidity of the crystal structure with a slight excess of Na insertion into layers between spinel blocks of the NaAl11O17 matrix. The nonequivalent substitution of Na+ by Eu2+ generates intrinsic defects acting as carrier traps. As a result, the phosphor with an optimal nominal composition Na1.6Al11O17+a :0.20Eu2+, under the excitation at 365 nm, shows an asymmetric cyan emission band at 468 nm with internal and external quantum efficiencies of 81.3 and 56.9%, respectively. Remarkably, the phosphor exhibits antithermal quenching within 200 °C. A pc-WLED with a high color rendering index (87.2) suggests great potential of the phosphor in pc-WLEDs. Therefore, a combination of a rigid structure and deep trap level is an effective way in exploring new phosphors with high quantum efficiency and thermal stability.

Highly-efficient Eu2+-activated Sr8Si4O12Cl8 cyan-emitting phosphors with zero-thermal quenching luminescence for versatile applications

“…The excitation spectrum, which is monitored at 492 nm, consisted of a broad band in the range of 250-450 nm arising from the absorption of Eu 2+ . 25,44 After excitation at 387 nm, the emission spectrum…”

“…Nowadays, Eu 2+ is the most widely used activator because of its intense broad emission band originating from the 4f 6 5d 1 → 4f 7 transition, in which the 5d 1 orbital is exposed to its surroundings. 24,25 In particular, the 5d 1 orbital is impacted by its surrounding crystal field environment, suggesting that the emission band of Eu 2+ can be varied from the ultraviolet to near-infrared by changing the different host materials. 26,27 Therefore, to make the Eu 2+ -activated phosphors exhibit good luminescence properties, the screening of suitable hosts is very important.…”

Oxygen vacancy content drives self-reduction and anti-thermal quenching

“…In addition, there are some other reported types, like Na 2 Al 11 O 17+d : Eu 2+ , K 2 Al 11 O 17+d :Eu 2+ , Na 3 Sc 2 (PO 4 ) 3 :Eu 2+ , and K 2 BaCa(PO 4 ) 2 : Eu 2+ . [17][18][19][20] Note that high temperature and pressure are necessary preparation conditions for the aforementioned hosts, and the activator ions also require the assistance of a reducing atmosphere at the same time. Nevertheless, the valence state of luminescent center is prone to being re-oxidized at long-term running, leading to chromaticity coordinate deviation.…”

Pressure-sensitive Ce3+ photoluminescence in LiCaY5(BO3)6: high internal quantum yields and energy transfer to Tb3+

“…White light-emitting diodes (WLEDs) are the predominant technique for solid-state lighting due to the advantages in high brightness, low power consumption, long duration and environmental friendliness. [1][2][3][4] The commercialized phosphor converted (pc)-WLEDs to combine the InGaN blue-emitting chip with the highly efficient yellow phosphor Y 3 Al 5 O 12 :Ce 3+ (YAG:Ce 3+ ), while the defect lies in the insufficient red component and the resulting high correlated color temperature and low color rendering index. 2,3,5 It is also possible to fabricate the ultraviolet (UV) or near-UV (NUV) LED chip with red, green, and blue phosphors to attain the white light properly.…”