Temperature and pressure dependence of the optical properties of Cr^{3 +}-doped Gd₃Ga₅O₁₂nanoparticles

Abstract

Since the crystal-field strength at the Cr(3+) site is very close to the excited-state crossover (ESCO), this work investigates the optical properties of Cr(3+)-doped Gd(3)Ga(5)O(12) (GGG) nanoparticles as a function of temperature and pressure in order to establish the effect of the ESCO on the optical behaviour of nanocrystalline GGG. Luminescence, time-resolved emission and lifetime measurements have been performed on GGG:0.5% Cr(3+) nanoparticles in the 25-300 K temperature range, as well as under hydrostatic pressure up to 20 GPa. We show how low temperature and high pressure progressively transforms Cr(3+)(4)T(2) --> (4)A(2) broadband emission into a ruby-like (2)E --> (4)A(2) luminescence. This behaviour together with the lifetime dependence on pressure and temperature are explained on the basis of the spin-orbit interaction between the (4)T(2) and (2)E states of Cr(3+).

Cr3+:SrGa12O19: A Broadband Near‐Infrared Long‐Persistent Phosphor

“…4 A 2 transition, which strongly depends on the crystal-field environment of the host. [6] Only a few Cr 3 + NIR long-persistent phosphors have been reported, and these are mainly limited to gallate materials, such as Cr 3 + :Zn 3 Ga 2 Ge 2 O 10 , [3] [8] and Cr 3 + :La 3 Ga 5 GeO 14 , [9] because of the strong ability of Cr 3 + to substitute for Ga 3 + (with a similar ionic radius) in octahedral coordination. Notably, most of the reported Cr 3 + -doped gallates have a narrow-band emission close to 700 nm since these gallates provide a strong crystal field environment for Cr 3 + ions.…”

“…Notably, most of the reported Cr 3 + -doped gallates have a narrow-band emission close to 700 nm since these gallates provide a strong crystal field environment for Cr 3 + ions. [6,10] Therefore, searching for novel hosts for Cr 3 + activator and realizing tunable Cr 3 + broadband long-persistent phosphorescence (LPP) are highly desired at present.…”

“…For NIR luminescence, Cr 3+ is an ideal activator in hosts since its 3d 3 electron configuration allows a narrow‐band emission (ca. 700 nm) due to the spin‐forbidden 2 E→ 4 A 2 transition, or a broadband emission (650–1600 nm) ascribed to the spin‐allowed 4 T 2 → 4 A 2 transition, which strongly depends on the crystal‐field environment of the host 6. Only a few Cr 3+ NIR long‐persistent phosphors have been reported, and these are mainly limited to gallate materials, such as Cr 3+ :Zn 3 Ga 2 Ge 2 O 10 ,3 Cr 3+ :LiGa 5 O 8 ,4b Cr 3+ :ZnGa 2 O 4 ,7 Cr 3+ :MgGa 2 O 4 8 and Cr 3+ :La 3 Ga 5 GeO 14 ,9 because of the strong ability of Cr 3+ to substitute for Ga 3+ (with a similar ionic radius) in octahedral coordination.…”

“…Only a few Cr 3+ NIR long‐persistent phosphors have been reported, and these are mainly limited to gallate materials, such as Cr 3+ :Zn 3 Ga 2 Ge 2 O 10 ,3 Cr 3+ :LiGa 5 O 8 ,4b Cr 3+ :ZnGa 2 O 4 ,7 Cr 3+ :MgGa 2 O 4 8 and Cr 3+ :La 3 Ga 5 GeO 14 ,9 because of the strong ability of Cr 3+ to substitute for Ga 3+ (with a similar ionic radius) in octahedral coordination. Notably, most of the reported Cr 3+ ‐doped gallates have a narrow‐band emission close to 700 nm since these gallates provide a strong crystal field environment for Cr 3+ ions 6. 10 Therefore, searching for novel hosts for Cr 3+ activator and realizing tunable Cr 3+ broadband long‐persistent phosphorescence (LPP) are highly desired at present.…”

Nanophosphors-Based White Light Sources

“…In this respect, to characterize the optical behavior carefully, low-temperature (i.e., around 10 K) spectroscopic measurements were performed to avoid thermal broadening of the spectral bands and disclose optical features related to the crystal-field allowed transitions of Cr as well as the temperature-dependence of the vibronic emissions. Spectra of Cr-doped GGG reported in the literature under different excitation conditions [145,164,165,166] indicate that Cr-doped GGG emits a featured spectrum with narrow lines stemming from the luminescence of Cr 3+ ions and vibronic side bands up to nearly 200–300 K. For increasing temperature, any structure is lost and the spectra become broadband-like. Instead our investigation of Cr-doped GGG revealed a completely different behavior under excitation conditions not reported by the available reports (laser excitation at 803.5 nm and larger intensity of pumping power (2 W)): a broadband unstructured WL emission profile was measured over a wide temperature range (from 33 to 300 K) without structural transitions [18].…”