Multicolour tuning and perfect white emission from novel PbWO4:Yb3+:Ho3+:Tm3+ nanophosphor

Abstract

Upconverting (UC) nanoparticles have been an unmatchable part for the people of optical world in the past decade because of their stupendous luminescence properties, photostability, effective quantum efficiency and most of all for its voluminous power of converting infra-red (IR) waves into visible radiation. In this article, we have successfully reported the synthesis of novel Yb3+, Ho3+, Tm3+ doped lead tungstate nanophosphor by facile hydrothermal technique, where the product can also be scaled up to a large quantity. The phase purity and structure of the samples were characterized using X-Ray diffractometer and the morphology was studied using FEG TEM which shows formation of nanospheres of average particle diameter ranging between (25–45) nm. Photoluminescence studies of the nanophosphor were carried out using spectroflurophotometer which shows red, green and blue emissions due to the energy level transitions viz. 5F5 → 5I8 and 5S2/5F4 → 5I8 of Ho3+,1G4 → 3H6 of Tm3+ respectively. The pumping power variation data was recorded using variable power which implies that the UC mechanism is a mixture of two and three photon processes. The biexponential decay kinetics measurement was also done using the pulse mode laser source which shows the mean lifetime of 21.1 μs, 12.03 μs and 30.44 μs for blue, green and red emission respectively. Due to the perfect intermixing of the red, green and blue emissions in the optimum sample, a bright white light is obtained with CIE co-ordinate indexed as (0.34573,0.3449). The correlated colour temperature (CCT) value of the bright white light was calculated using McCamy’s approximations and it was found to be 4960 K which is almost equivalent to the colour “Horizon Daylight”. The colour temperature found after calculation, is eye-friendly and hence perfect for optoelectronics applications.