Color tuning in CaZrO3:RE3+ perovskite by choice of rare earth ion

Abstract

Color tunable phosphor has been attracting the scientific community owing to its multifunctional application in optoelectronics, solid-state lighting and bioimaging. Achieving the same in a single host will be quite interesting from a designer’s perspective in narrowing down the cost and scaling it. In the current work, we have explored gel-combustion synthesized rare earth (RE) doped CaZrO3 (CZO) perovskite as a phosphor for covering a wide range of tunable colors ranging from ultraviolet (UV) → Visible. We have doped different rare earth ions such as Sm3+, Eu3+, Gd3+, and Tb3+ in CZO and explored their optical properties, local structure, excited-state lifetime, etc. Doping of RE ions in CZO leads to efficient luminescence facilitated by host→dopant energy transfer. CaZrO3:Sm3+(CZOS) displayed reddish-orange emission with two different lifetime values viz. 20 and 72 μs and are attributed respectively to Sm3+ ion located at Zr4+ (24%) and Ca2+ (76%) sites, respectively. CaZrO3:Eu3+(CZOE) on the other hand, displayed bright, highly pure, and narrow red emission with incredibly low non-radiative transition probability (ANR), high red branching ratio (β2) with internal quantum yield (IQY) of 71.4%. Based on the Stark splitting investigation; europium symmetry in CZOE was found to be quite low with the C6 point group. The lifetime of CZOE though suggested biexponential decay, but Eu3+ ions are localized only at Ca2+ ion; one closer to charge compensating calcium vacancies (194 μs) and other (425 μs) at far off distance from the same. CaZrO3:Gd3+(CZOG) emits highly energetic UV radiation, which can be quite useful in photothermal therapy. Lastly CaZrO3:Tb3+(CZOT) phosphor emits bright green light, but it is displaying a single exponential decay profile stabilizing only on symmetric Zr4+ sites as suggested by the intense magnetic dipole transition (MDT). We believe such a complete spectrum of work in designing a tunable phosphor would be quite beneficial in phosphor converted light emitting diodes (pc-LEDs) employing red-green-blue (RGB) strategy.