This paper reports a temperature-dependent (10-280 K) photoluminescence (PL) study of belowbandgap electron-hole recombinations and anomalous negative thermal quenching of PL intensity in InP 1-x Bi x (x ¼ 0.019 and 0.023). Four PL features are well resolved by curve-fitting of the PL spectra, of which the energies exhibit different temperature dependence. The integral intensities of the two high-energy features diminish monotonically as temperature rises up, while those of the two low-energy features decrease below but increase anomalously above 180 K. A phenomenological model is established that the residual electrons in the final state of the PL transition transfer into nonradiative state via thermal hopping, and the thermal hopping produces in parallel holes in the final state and hence enhances the radiative recombination significantly. A reasonable interpretation of the PL processes in InPBi is achieved, and the activation energies of the PL quenching and thermal hopping are deduced. Published by AIP Publishing. Temperature-dependent photoluminescence (PL) as a powerful probe has been widely employed for characterizing electron-hole recombinations in semiconductors. In particular, the evolution of PL intensity with temperature reveals nonradiative recombination mechanisms:1-3 as temperature rises up, the nonradiative centers in semiconductor capture carriers result in a monotonic quenching to the PL integral intensity. The quenching can be described by a multi-center model 4,5 IðTÞwhere I 0 is the integral intensity before quenching, C q is the nonradiative coefficient being relevant to the carriers lifetime, capture coefficient and effective density of states, and k B and E q are Boltzmann constant and activation energy of the quenching, respectively. Dilute-bismuth (Bi) III-V semiconductors are very promising for possible long-wavelength opto-electronic applications of laser diode, 6 light emitting diode, 7 and photodetector, 8 due to the Bi-induced bandgap shrinkage and spinorbit enhancement.9-11 The PL evolution with temperature in dilute-Bi III-V semiconductors has attracted extensive attention.12-14 For example, it was clarified for GaAsBi that the thermal quenching of bandedge PL is due to two-energy components of cluster localization and alloy disorder.12 For InP 1-x Bi x , which is compatible with InP-based devices and the bandgap reduction is as large as 60-80 meV/%Bi, [15][16][17][18][19] however, the bandedge PL emission is missing and an extraordinarily broad below-bandgap PL emission shows up in a range of 0.9-2.5 lm.15-17 While such a broad-band PL emission may open up a new application window for, e.g., super-broad infrared source covering the whole telecommunication spectral range, the thermal quenching of the broadband PL is yet to be clarified.We in this paper report a temperature-dependent PL study of two InP 1-x Bi x (x ¼ 0.019 and 0.023) epilayers, with a focus on the integral intensity evolution of the belowbandgap PL transitions. The PL integral intensity diminishes with temperature...