Synthesis and optical properties of Li3Ba2La3(MoO4)8:Eu3+ powders and ceramics for pcLEDs

Abstract

A series of polycrystalline Li 3 Ba 2 La 3Àx Eu x (MoO 4 ) 8 samples were prepared by the conventional solidstate reaction. The phase formation of the samples was investigated by X-ray diffraction measurements. The luminescence spectra and decay curves were studied as a function of Eu 3+ concentration and temperature. It turned out that the optical band gap of the undoped molybdates is at 3.65 eV. The quantum efficiency (QE) of the Eu 3+ doped luminescent materials increases with increasing Eu 3+ concentration and almost 100% QE was obtained for those samples doped with 70, 80, or 90% Eu 3+ . A sample containing 100% Eu 3+ showed solely a slight decrease in quantum efficiency. The luminous efficacy (LE) was 330 and 312 lm W opt À1 for the 10 and 100% Eu 3+ doped samples, respectively. The decrease of LE values is caused by a slight shift of the colour point to the red spectral range with increasing Eu 3+ content. Temperature dependent measurements revealed that Li 3 Ba 2 Eu 3 (MoO 4 ) 8 loses only 15% of efficiency up to 400 K, which demonstrates that the investigated phosphors are attractive for application in pcLEDs.

Effect of cation vacancies on the crystal structure and luminescent properties of Ca 0.85−1.5x Gd x Eu 0.1 □ 0.05+0.5x WO 4 (0 ≤ x ≤ 0.567) scheelite-based red phosphors

“…However, the application of these materials is hampered by the weak absorption strength of the parity forbidden 4f 6 -4f 6 transitions, which limits the excitation of Eu 3+ with blue or near-UV light [16]. This problem can be partially alleviated by increasing the optical path length or by increasing the concentration of luminescent centers [17]. However, at high concentrations the internal quantum efficiency decreases owing to the energy transfer to non-radiative defect centers, i.e.…”

Inorganic Phosphor Materials for Lighting

“…So, a NUV chip can be used to excite red emission efficiently. This concept was proposed by Bettinelli et al [149] [151] and, therefore, to higher emission intensity. However, this is not the case, as the increased concentration of the activator ions usually results in a decrease of the emission QE.…”

“…If these ions are kept a long way apart one from another by large, bulky anions, high QEs can be achieved even for fully concentrated hosts. Good results have been obtained for concentrated molybdates [151] in which concentration quenching is prevented by the presence of large anions between Eu 3? centers.…”

“…As mentioned above, molybdate, tungstate, niobate, and tantalate hosts activated with Eu 3? have been widely investigated [151][152][153][154][155][156][157][158][159][160][161][162][163][164][165][166][167], also exploting co-doping with Sm 3? , but only in a limited number of cases the two strategies described above (high Eu 3?…”

Luminescence and luminescence quenching of Eu 2 Mo 4 O 15

“…The absorption intensity of optical transitions at higher energies (< 400 nm) get especially strong due to admixing with charge transfer (CT) band, which is allowed one. This phenomenon is exploited in manufacturing of very bright Eu 3+ doped molybdate phosphors with extremely high quantum yields [15,16]. Powder XRD pattern was recorded in the range of 10° ≤ 2θ ≤ 80° (step width 0.02° and scanning speed 5 °/min.)…”