Luminescence properties of tungstates and molybdates phosphors: Illustration on ALn(MO4)2 compounds (A = alikaline cation, Ln = lanthanides, M = W, Mo)

Abstract

are analyzed as a function of their structure. The influences of cation size and electronegativity are discussed in relation with the Struck and Fonger theory, with a view to developing one or more of those compounds as phosphors in relation with the development of white LEDs. It appears that there are various excited states implied in the absorption process, with partially radiative transfer between them. All the radiative mechanisms are strongly related to temperature. Due to their electronegativity, tungstate compounds are the most promising, compared to molybdate ones, especially those in the monoclinic P 2/n structure.

Novel morphology of needle-Like nanoparticles of Na2Mo2O7 synthesized by using Ultrasonic spray pyrolysis

“…The effective heating length of reactor tube was 1 m with the maximum temperature of 300 °C in the middle of the furnace. The flow rate of air was 30 dm 3 per hour. The droplet velocity, calculated from the ratio of the carrier gas flow to the reaction zone area (0.5 × 10 -3 m 2 ), was 0.017 m/s.…”

“…Molybdate compounds have been extensively studied for solid-state lighting with light emitting diodes. In most cases, this structure is luminescent ion hosts in order to obtain a well defined emission property 3,4 . On the other side, sodium dimolybdate (Na 2 Mo 2 O 7 ) belongs to the class of sodium molybdates with the general composition Na 2 Mo n O 3n+1 [5,6] .…”

Structure and light emission of scheelite-type <i>A</i>Ce(WO₄)₂ (<i>A</i> = Li, Na, or K)

“…In addition, tungstates have been attracting interest for use in host materials doped with a trivalent lanthanide ion, acting as the activator. These materials exhibit high potential for a wide range of applications, such as in phosphorescent materials, 6) solar cells, 7) optical fibers, 8) or luminescent diodes. 9) These materials have the A 2+ WO 4 2¹ or A + B…”

Estudo da preparação de microcristais de LiLa(WO4)2:TR3+ para aplicações fotônicas

“…Sua temperatura de fusão (pico) é de 1040°C e não sofre transformação estrutural polimórfica [30]. A matriz LLW é naturalmente fotoluminescente numa larga banda no intervalo aproximado de 350 -700 nm, fenômeno relacionado ao grupo (WO4) 2- [102].…”

“…Contudo, tal luminescência é de baixa intensidade, se comparada com a emissão de íons ativadores ópticos, e depende das distorções presentes na rede devido à distribuição aleatória do Li e do La [102]. A anisotropia de expansão térmica para o LLW é relativamente pequena [27], pois a razão entre os coeficientes de expansão térmica nos eixos a e c (αc/αa =1,9) é menor do que a de outros tungstatos duplos como o NaY(WO4)2 (5,05) e o NaGd(WO4)2 (2,43).…”