Broadband, White Light Emission from Doped and Undoped Insulators

Abstract

We present data on broadband, white light emission from insulating hosts under intense excitation in the near infrared in host materials that are undoped, partially-doped with rare earth ions, and that contain stoichiometric concentrations of rare earth ions. Much of the emission is found to have a blackbody-like structure in the visible and near infrared region. The origin of the emission as from a blackbody is also supported by the temporal characteristics of the emission in response to turning on and off the laser, and also by the dependence of the air pressure in the chamber. However, some of the data presented cannot be explained by blackbody emission alone, so other processes are proposed to explain the observed spectra. The role of the rare earth ion dopants in enhancing the broadband emission is also considered. Over the last several years, numerous works have reported a broadband, white-light emission from insulating powders under intense, near infrared (IR) excitation. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] The materials investigated are usually nano-powders of insulators, such as yttrium oxide, yttrium silicate, Al 2 O 3 , GGG, and others, either pure or doped with rare earth ions (e.g. Er, Nd, Yb, Tm) or transition metal ions (e.g. Cr). Spectral and temporal characteristics of the broadband emission suggest that it is thermal in origin. One study on the origin of the emission, conducted by Debasu et al.,16 concluded that the emission is indeed blackbody emission, with temperatures in the range of ∼1200 K-1900 K. We have studied the white-light emission phenomenon in several host materials, both doped and undoped. In this work, we present results representative of this body of work, and we consider how these results fit into the blackbody model.For lighting applications, one of the main goals is the generation of high quality, white light with highest possible efficiency. Broadband white light based on blackbody-like emission can be of very high quality, but it is never efficient, especially compared to compact fluorescent or LED-based lighting. The white light we report on here is probably no different in that regard, and so it likely will be of little usefulness as a general lighting source. One difference between these emitters and tungsten-based blackbody sources is the means by which energy is delivered to the system; the energy source is a near infrared diode laser instead of electrical power converted to Joule heating, as in a tungsten lamp.Production of white light using near IR photons can occur in different ways. One method of recent interest is the upconversion process in rare earth doped systems that depend on energy transfer and/or excited state absorption to produce emission of high-energy photons. Usually, this occurs in systems co-doped with, for example, Yb, Er and Tm, 20,21 and the emission is exclusively from the f-f transitions of the dopant ions. The white light reported on here is generated in a fundamentally different way. The energy contained in the...

Optically Driven Tunable Transistor Effect at Matter/Vacuum Interface—Toward Dielectric Optical Transistors

“…500 °C), and saturation of the WLE intensity for higher excitation powers), thus several different theories have already been proposed for interpretation of the WLE phenomenon. Those propositions include cooperative emission, up-conversion emission following multiphoton absorption, thermal radiation, , photon avalanche, supercontinuum generation, or intervalence charge transfer (IVCT). , The latter deserves closer attention, as formation of mixed valence pairs, i.e., Yb 3+ and Yb 2+ , may not be ignored during intense pumping with the 975 nm CW laser in a vacuum. In such a case, the charge transfer process may occur either by optical or thermal excitation.…”

“…The WLE phenomenon of insulating nanophosphors was first observed and described by Wang and Tanner in 2010, who had studied an odd broadband emission from Yb 2 O 3 , Sm 2 O 3 , and CeO 2 powders that occurred under intense 975 nm laser excitation . Due to its untypical character, the WLE was first seen as a new type of cold emission and further investigated by a number of researchers, showing its anti-Stokes character that was in many ways quite similar for a broad range of various materials, including graphene, metals, or oxides. − The WLE reveals a number of uncommon properties, i.e., (i) broad-band emission, (ii) independence on the excitation wavelength, (iii) threshold behavior of light emission, (iv) sensitivity to the vacuum level, (v) moderate average temperature (lower than ca. 500 °C) of the emitting sample, or (vi) multiphoton character.…”

Blackbody emission from CaF2and ZrO2nanosized dielectric particles doped with Er3+ions

“…A vivid example is the appearance of broadband "white" emission (BBWE) in nanoscale dielectric materials when they are excited by intense laser radiation. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] In most cases, this emission was observed in compounds doped with rare-earth (RE) ions upon excitation into the absorption band of these ions. An analysis of these publications indicates that there are different points of view on the nature of the observed phenomenon and the processes responsible for it.…”

“…The rst group of researchers believes that the observed emission is inherently thermal (blackbody). 1,5,[11][12][13][14] According to the second group of opinions, it represents luminescence and is not associated with sample heating. 2,3 For example, the authors of 1,5 attribute the thermal nature to the BBWE observed when the nanosized particles of Y 2 O 3 :Yb,Er are excited into the absorption band of Yb 3+ ions.…”

Host‐Sensitized Continuum‐Broad‐Band White‐Light Emitting Yb2O3:Er3+ Phosphor under CW‐NIR Light Absorption

“…Also, S. Tabanli et al. have reported the white light emission from the Yb 2 O 3 at 1 atm and at 0.03 mbar pressure . However, the heat associated/incandescent‐like white light of continuum spectrum and IOB produced by host sensitized Yb 2 O 3 :Er 3+ phosphor under 980 nm CW laser diode excitation has not been reported till date.…”