Rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors for intense white light-emitting diodes

Abstract

The commercially available white-light-emitting diodes (WLEDs) are made with a combination of blue LEDs and yellow phosphors. These types of WLEDs lack certain properties which make them meagerly applicable for general illumination and flat panel displays. The solution for such problem is to use near-ultraviolet (NUV) chips as an excitation source because of their high excitation efficiency and good spectral distribution. Therefore, there is an active search for new phosphor materials which can be effectively excited within the NUV wavelength range (350–420 nm). In this work, novel rare-earth free self-luminescent Ca2KZn2(VO4)3 phosphors were synthesized by a citrate assisted sol-gel method at low calcination temperatures. Optical properties, internal quantum efficiency and thermal stability as well as morphology and crystal structure of Ca2KZn2(VO4)3 phosphors for their application to NUV-based WLEDs were studied. The crystal structure and phase formation were confirmed with XRD patterns and Rietveld refinement. The optical properties of these phosphor materials which can change the NUV excitation into visible yellow-green emissions were studied. The synthesized phosphors were then coated onto the surface of a NUV chip along with a blue phosphor (LiCaPO4:Eu2+) to get brighter WLEDs with a color rendering index of 94.8 and a correlated color temperature of 8549 K.

Origin of Luminescence in La2MoO6 and La2Mo2O9 and Their Bi-Doped Variants

“…titanates, vanadates, niobates, tantalates, molybdates, tungstates) appear as an excellent alternative. 8,9 With this in mind, we have embarked on the elucidation of the luminescent properties of lanthanum molybdenum oxides (LMO) and their bismuth doped derivatives (LMO:Bi).…”

Luminescence in external dopant-free scandium-phosphorus vanadate solid solution: a spectroscopic and theoretical investigation

“…82 As a result, in most cases, the self-activated phosphors usually can only show QE values less than 50%, such as those summarized by Dang et al, 83 Huang et al, 84 and Zhou et al, 85 83 and those summarized by Huang et al, 84 and Zhou et al 85 Looking into the IQE and/or EQE values we obtained, it is obvious that some of them, typically for the Sc(P 0.3 ,V 0.7 )O 4 sample, are comparable to and can even be higher than those of many reported self-activated phosphors and some other RE/non-RE doped crystals, such as ScVO 4 :0.02Bi 3+ (l ex = 330 nm xenon lamp, EQE = 35%), 25 CsPbCl 3 (l ex = 360 nm xenon lamp, QY = 26.0 AE 0.3%), 90 Cs x K 1Àx PbCl 3 :Eu 3+ (l ex = 365 nm xenon lamp, EQE = 31.2%), 91 and CsPbCl 3 :Mn 2+ (l ex = 360 nm xenon lamp, QY = 27%). 92 Moreover, the improved thermal stability (T 50% ) of 480.15 K and/ or activation energies (DE a ) of 0.51 eV for the Sc(P 0.4 ,V 0.6 )O 4 solutions are also higher than or comparable to those of some RE/non-RE doped phosphors, for example, La 2 MgTiO 6 :0.005Bi 3+ (l ex = 350 nm xenon lamp, T 50% = B175 1C, DE a = 0.27 eV), 4 La 2 MgTiO 6 :0.005Bi 3+ (l ex = 410 nm xenon lamp, T 50% = B250 1C, DE a = 0.252 eV), 6 CaSc 2 O 4 :Ce 3+ (l ex = 437 nm, T 50% = B225 1C, DE a = 0.195 eV), 60 (DE a = 0.469 eV, T 50% = B60 1C), 94 CsVO 3 (DE a = 0.31 eV). 95 More importantly, the fundamental aspects this work provided can deepen the understanding of the intrinsic working principle of the PL color tuning, enhanced PL intensity and improved thermal stability appeared in future spectrally tunable inorganic solid solutions.…”

In‐doped LiCa2.98MgV3O12 rare‐earth‐free phosphor with a high photoluminescence quantum yield of 67.4%

“…20,21 The vanadate phosphor with the photoluminescence properties have attracted much attention. 22,23 Vanadate phosphors usually have broadband UV absorption, broadband emission and a certain conversion efficiency for WLED, and the [VO 4 ] in the vanadate phosphor is an efficient luminescent center, in which the central vanadium ion coordinates with the tetrahedral (T d ) symmetrical four oxygen ions. 20 These self-activated phosphors of vanadium own many merits over rare-earth-active phosphors.…”