Enhanced luminous efficiency in Pr3+ activated Ca0.5La(MoO4)2 red phosphor with blue excitation for WLED applications

Abstract

In this article, we have investigated the downconversion luminescence properties of Ca 0.5 La(MoO 4 ) 2 doped with trivalent Pr 3? (substitute for La 3? site) and codoped with Mn 2? (substitute for Ca 2? site). The powder X-ray diffraction patterns confirm that the single crystalline phosphor powders belong to the scheelite-type tetragonal crystal structure. The photoluminescence (PL) excitation spectra of Ca 0.5 La(MoO 4 ) 2 :Pr 3? exhibits a charge transfer band centered at 276 nm along with three intense sharp absorption bands identified at 449, 475, and 488 nm which are attributed to the f-f electronic transitions of of Pr 3? , respectively. Upon optical excitation, the depopulation of excited 3 P 0 level into the 3 F 2 lower levels of Pr 3? is governed by radiative transfer of energy, as a result, high intense red emission peak was observed at 647 nm. The change in PL emission intensity as a function of Pr 3? concentrations, Mn 2? concentrations, and different excitation wavelengths have been investigated in detail. Further, the codoping of alkali metal chlorides MCl (M = Na, K, Li) into the Ca 0.5 La(MoO 4 ) 2 :Pr 3? phosphor greatly improves the luminescence intensity of the transition 3 P 0 ? 3 F 2 which can be explained by charge compensation effect. To ensure the colour richness and quality of its emission, the photometric parameters were estimated using spectral energy distribution functions of Ca 0.5 La(MoO 4 ) 2 :Pr 3? .The luminous efficacy of radiation for NaCl codoped Ca 0.5 La(MoO 4 ) 2 :Pr 3? phosphor was estimated to be 154 lm/W and the percentage of luminous efficiency is 23 %.