Enhanced luminous efficiency in Pr super(3+) activated Ca sub(0.5)La(MoO sub(4)) sub(2) red phosphor with blue excitation for WLED applications

In this article, we have investigated the down-conversion luminescence properties of Ca sub(0.5)La(MoO sub(4)) sub(2) doped with trivalent Pr super(3+) (substitute for La super(3+) site) and codoped with Mn super(2+) (substitute for Ca super(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 sub(0.5)La(MoO sub(4)) sub(2):Pr super(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 super(3)H sub(4) super((1)) arrow right super( 3)P sub(2), super(3)H sub(4) super((1)) arrow right super( 3)P sub(1), super(3)H sub(4) super((1)) arrow right super( 3)P sub(0) of Pr super(3+), respectively. Upon optical excitation, the depopulation of excited super(3)P sub(0) level into the super(3)F sub(2) lower levels of Pr super(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 super(3+) concentrations, Mn super(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 sub(0.5)La(MoO sub(4)) sub(2):Pr super(3+) phosphor greatly improves the luminescence intensity of the transition super(3)P sub(0) arrow right super(3)F sub(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 sub(0.5)La(MoO sub(4)) sub(2):Pr super(3+). The luminous efficacy of radiation for NaCl codoped Ca sub(0.5)La(MoO sub(4)) sub(2):Pr super(3+) phosphor was estimated to be 154 lm/W and the percentage of luminous efficiency is 23 %.